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The Hydroboost System is used on many different chassis
- Dodge Motorhome Chassis (76 and later)
- Chevrolet/GMC P30 Motorhome Chassis
- Ford F53 Motorhome Chassis
- John Deere / Oshkosh / Freightliner Motorhome Chassis
DESCRIPTION
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The Hydroboost system utilizes power steering pump fluid pressure to operate booster. The booster assembly contains an open center spool valve which controls pump pressure magnitude during braking, a lever mechanism to control position of valve, and a boost piston to provide the force necessary to operate the master cylinder. The booster unit also has a reserve system which stores sufficient fluid under pressure to provide at least two braking applications in case fluid flow from power steering pump is not available. Brakes can also be applied manually if reserve system is depleted.
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Front Disk / Rear Drum(https://www.classicwinnebagos.com/forum/proxy.php?request=http%3A%2F%2Fi286.photobucket.com%2Falbums%2Fll120%2FBaileyDave%2FHydroboost%2FBrake_System_zps218d33e4.gif&hash=906614bd9193485242e298f66283a5b4e596f1ce)
4 Wheel Disk(https://www.classicwinnebagos.com/forum/proxy.php?request=http%3A%2F%2Fi286.photobucket.com%2Falbums%2Fll120%2FBaileyDave%2FTag%2520Brakes%2FTagHydroboostDiagramLg.jpg&hash=fba18f89e7c156ac7c75077208b0135796e6053a)
4 Wheel Disk with Drum Tag AxleNote: Please refer to the Tag Axle Break Thread for information about that portion
OPERATIONRELEASED POSITION (NO BRAKING)ln this position, spool valve return spring holds spool valve open. In open position, spool valve provides unrestricted fluid flow between power steering pump and power steering gear. Fluid pressure is blocked from entering boost pressure chamber by lands on spool valve. As fluid pressure increases with steering demand, it has no effect on boost pressure chamber. Boost pressure chamber is vented through spool valve, to pump return port, and back to power steering pump.
BRAKING POSITIONAs brake pedal is depressed, it moves pedal rod and initiates movement of spool valve. This closes fluid return port to pump from boost chamber, and admits fluid into boost chamber from pressure port. Additional valve movement restricts flow between pump and steering gear, causing pump to increase fluid pressure to maintain flow rate to steering gear. As fluid pressure increases in boost chamber, it forces piston forward actuating master cylinder piston, resulting in brake application. lf fluid pressure is required for steering while braking, pump pressure will rise and spool valve will shift in an open direction allowing more fluid to flow to steering gear.
RESERVE SYSTEM1) System consists of a charging valve, accumulator valve, and a spring loaded accumulator. Accumulator is integral with booster unit. System is open to pressure port of booster unit. Charging valve has an orfice and ball check. Fluid from pump passes through orfice in the valve, and if pressure exceeds pressure in accumulator, it unseats ball check valve and enters accumulator. Ball check valve prevents reverse flow when accumulator pressure is greater.
2) Accumulator valve is a poppet type valve held closed by pressure stored in accumulator. An actuator on spool valve sleeve opens accumulator valve when a stop with no pump pressure is made that requires use of reserve pressure. Fluid pressure can also enter accumulator from boost chamber through accumulator valve, when boost chamber pressure exceeds accumulator pressure. A pressure relief valve vents accumulator to pump return port when pressure in accumulator exceeds approximately I600 psi.
ADJUSTMENT
BRAKE PEDALChevrolet & GMC (MHC Only)With brake return spring installed, brake pedal should return hard into rubber stop, and master cylinder and pedal rod lever should be at lull return. Install pre·assembled brake pedal rod assembly (rod, end and boot). Adjust brake pedal rod to 3l.75" and adjust rod end until pedal free play is .06·,36â€. Fasten boot to floor pan and compress to an installed height of 2.54". Pedal travel (with engine off and accumulator depleted) should not be more than 6" under a 90 lb. load,
Dodge ("M" Models)l) Disconnect wiring at rear of stop light switch. loosen lock nut at switch and loosen switch until plunger is no longer contacting pedal. Disconnect pedal return spring. Loosen pedal stop lock nut and remove shouldered push rod end bolt and pedal return spring bracket.
2) Place a .010 - .0l5" spacer between pedal and stop. Turn stop in or out until shouldered bolt can be easily inserted in pedal and push rod. Install return spring bracket and tighten pedal stop nut. Remove spacer and connect return spring. Tighten stop light switch until plunger just contacts pedal and then turn an additional 2 I/2 turns. Tighten switch lock nut and connect wiring.
TESTING
NOTE: Hydroboost cannot cause noisy brakes, fading brake pedal, or pulling brakes. If one of these conditions exists, other components of brake system are at fault.
PRELIMINARY CHECKSCheck fluid levels in master cylinder and power steering pump. Check power steering pump belt tension, and adjust if necessary. inspect all power steering hoses for leaks or kinks. lf fluid smells burned, check hoses or cooler for restrictions. Check and adjust engine idle speed. Check power steering hydraulic fluid for operation (shown by bubble in fluid), bleed system it necessary.
NOTE: lf problem cannot be found in preliminary steps, make following tests. lf unit is found to be operating properly, check areas of brake system that might cause condition. See Hydraulic Brake Trouble Shooting in this section.
HYDROBOOST FUNCTIONAL TESTCheck hydraulic brake system for leaks or insufficient fluid in master cylinder reservoir. With transmission in Neutral, stop engine and apply brake pedal several times to deplete all accumulator reserve. Hold brake pedal depressed with medium pressure (approx. 25·35 lbs.) and start engine. If unit is operating correctly, brake pedal will fall slightly and then push back against foot. If no action is felt, hydraulic booster system is not operating.
ACCUMULATOR LEAKDOWN TEST1) Start engine and operate at idle speed. Turn steering wheel to either â€Stop" and hold in this position for a maximum of five seconds. Return steering wheel to center position and turn off engine. Depress and release brake pedal. Repeat procedure until ¤ hard pedal is obtained. There should be at least two power assisted brake applications with 20-25 lbs. pressure applied to brake pedal.
2) Restart engine and let it idle. Turn steering wheel to either "Stop". There should be a light hissing sound as accumulator is charged. Hold steering wheel lightly against "Stop" for a maximum of five seconds. Return steering wheel to center position and turn oft engine. Wait one hour and apply brake pedal
(DO NOT re-start engine before applying brake). There should still be at least two power assisted brake applications at 20-25 lbs. pressure before a hard pedal is encountered.
NOTE: If Hydroboost is not functioning, insure power steering system is operating normally before replacement or overhaul of Hydroboost unit.
HYDROBOOST UNIT REMOVAL & INSTALLATION
CHEVROLET & GMCUnit Removal1) Depress and release brake pedal several times to be sure that all pressure is discharged from accumulator prior to disconnecting hoses from booster. Raise Motor Home Chassis on hoist; all others, leave on ground. Clean all dirt from booster at hydraulic line connections and master cylinder. Remove nuts that secure master cylinder to booster and support bracket. Support master cylinder, and cover exposed end with clean cloth.
NOTE: ln most cases, il is not necessary to disconnect master cylinder hydraulic lines to remove booster unit.
2) On all models except Motor Home Chassis, remove booster pedal push rod cotter pin and disconnect push rod from broke pedal ("C†& "G" models) or from booster bracket pivot lever ("P" models). Remove booster support bracket ("C" & "G" models) or support braces ("P" models). Remove booster bracket-to-firewall or support bracket nuts and remove booster assembly.
3) On Motor Home Chassis, remove cotter pin, nut and bolt that secure operating lever to vertical brake rod, Remove the six nuts and bolts that secure booster linkage bracket to front and rear support brackets, and remove booster from vehicle by sliding booster off rear support studs. Remove cotter pin, nut, and bolt that secures operating lever to pedal rod. Remove brake pedal rod lever nut and bolt and then remove lever, sleeve and bushings.
lnstallation:To install, reverse removal procedure noting the following:
Lubricate pedal rod and linkage pivot bolts,pins, sleeves and bushings with suitable lubricant (Delco Brake Lube 5450032).
Bleed booster/power steering hydraulic system.
NOTE: This is a separate procedure from bleeding hydraulic brake system. See Bleeding Hydroboost System in this Article. Check brake pedal and stoplamp switch adjustment.
DODGE ( Motorhome Chassis)RemovalDepress and release brake pedal several times to be sure that all pressure is discharged from accumulator. Disconnect and plug hoses from booster. Remove master cylinder nuts ond lay master cylinder to side without kinking lines. Disconnect broke return spring. Remove brake pedal push rod bolt, remove mounting nuts and booster.
InstallationTo install unit, reverse removal procedure. Tighten all nuts and hose connections. Bleed booster/power steering hydraulic system.
NOTE: This a separate procedure from bleeding hydraulic system. See Bleeding Hydroboost System in this article. Check brake pedal and stop lamp switch adjustment.
BLEEDING HYDROBOOST SYSTEM
CHEVROLET & GMCNOTE: lf power steering fluid has foamed due to low fluid level, it will be necessary to park vehicle for approximately one hour (reservoir cap loose) so that foam can dissipate.
1) Raise front of vehicle on o hoist so that tires are clear of floor. Check reservoir and fill with suitable power steering fluid (GM Power Steering Fluid).
NOTE: Leave reservoir cap off during entire bleed procedure. Install a remote control starter switch so that engine can be cranked but not started.
CAUTION: Whenever engine is cranked with a remote starter, or other means, distributor primary lead must be disconnected from negative post on coil.
2) Crank engine for four to five seconds while pouring fluid into reservoir. Fill reservoir and crank engine until system will no longer accept fluid. lt is normal that fluid may spill from filler tube when cranking stops. Remove remote control starter switch and reconnect distributor wire. Start engine and run for two seconds. Check and refill reservoir if necessary.
3) Start engine and depress brake pedal several times while rotating steering wheel from "Stop" to "Stop". Turn engine off and then pump brake pedal four to five times to deplete accumulator pressure. Check and refill reservoir if necessary.
Repeat step 3). Install reservoir cap.
DODGE (Motorhome Chassis)1) Check power steering pump reservoir and fill with suitable power steering fluid (MOPAR Power Steering Fluid). Allow fluid to remain undisturbed for two minutes. Leave reservoir cap off during bleeding operation.
2) Start engine and run for ten seconds. Check fluid level and add fluid if necessary. Repeat procedure until fluid level remains constant. Raise front of vehicle and allow tires to clear floor. Start engine and run at l500 RPM. Apply and release brakes several times, at the same time turn wheels back and forth, lock to lock. Turn off engine ond check fluid level. Add fluid if necessary.
3) Lower vehicle. Start engine and run at l50O RPM. Apply and release brake pedal several limes, at the same time turn front wheels back and forth, lock to lock. Turn off engine and check fluid level. Add fluid if necessary. If fluid level is low, repeat bleeding procedure. Place cover on reservoir.
Hydroboost Unit Diagnosis
CONDITION | CAUSE | CORRECTION |
Excessive Brake Pedal Effort | Loose or broken power steering pump belt. | Tighten or replace the belt. |
| No fluid in power steering reservoir | Fill reservoir and check for external leaks. |
| Leaks in Hydro-Boost | Replace faulty parts. |
| Leaks at Hydro-Boost tube fittings | Tighten fittings or replace tube seats, if faulty. |
| External leakage at accumulator | Replace "0" ring and retainer. |
| Faulty booster piston seal causing
leakage at booster flange vent | Overhaul with new seal or input rod and piston assembly. |
| Faulty booster input rod seal with
leakage at input rod end. | Overhaul with new seal kit. |
| Faulty booster cover seal with
leakage between housing and cover. | Overhaul with new seal kit. |
| Faulty booster spool plug seal. | Overhaul with spool plug seal kit. |
|
|
|
Slow Brake Pedal Return | Excessive seal friction in booster. | Overhaul with new seal kit. |
| Faulty spool action. | Flush steering system white pumping brake pedal. |
| Restriction in return line from
booster to pump reservoir. | Replace line. |
| Damaged input rod end. | Replace input rod and piston assembly. |
|
|
|
CONDITION | CAUSE | CORRECTION |
|
|
|
Grabby Brakes | Faulty spool action caused by
contamination in system. | Flush steering system white pumping brake pedal. |
|
|
|
Booster Chatters
Pedal Vibrates | Power steering pump belt slips. | Tighten belt. |
| Low fluid level in power steering
pump reservoir. | Fill reservoir and check for external leaks. |
| Faulty spool operation caused by
contamination in system. | Flush steering system while pumping brake pedal. |
|
|
|
Accumulator Leak Down
System does not hold charge | Contamination in steering hydro-boost
system | Flush steering system while pumping brake pedal |
| Internal leakage in accumulator system. | Overhaul unit using accumulator rebuild kit and seal kit. |
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Chevrolet/GMC Combination ValveThe brake warning switch is used to indicate a failure in either front or rear hydraulic system. The metering valve is used to better balance the hydraulic system during certain braking conditions.
Brake Warning Switch Unit The brake warning switch used in these combination valves are latching types. If a pressure loss occurs in one side of the dual brake system the piston in the valve will move toward the failed side and latch in that position. This will cause the brake system warning light to come on and stay on until the brake system is repaired. After repairing and bleeding the brake system, applying the brakes with moderate force will hydraulically recenter the piston and automatically turn off the warning light.
DO NOT DISASSEMBLE THE VALVE TO RESET THE PISTON. Testing Brake Warning Switch Unit
The brake warning light bulb function can be tested by starting the engine. The light will go on when the ignition key is turned to the extreme right START position and will go off as soon as the engine starts.
To test the service brake warning system, raise the car on a hoist and open a wheel cylinder bleeder while a helper depresses the brake pedal and observes the warning light. If the light fails to light, inspect for a burned out bulb, disconnected socket, a broken or disconnected wire at the switch. If the bulb is not burned out and the wire continuity is proven, replace the brake warning switch in the brake line Tee fitting mounted on the frame rail.
Metering Valve Unit (Rear Drum Brakes only)
The metering valve holds of hydraulic pressure to the front disc brakes in the 35 to 135 psi range to allow the rear drum brake shoes to overcome the return springs and begin to contact the drums. This feature helps prevent locking the front brakes on icy surfaces under light braking conditions. The metering valve has no effect on front brake pressure during hard stops.
Proportional ValveThe rear brake proportioner improves front-to-rear brake balance at high deceleration. During high deceleration stops, a percentage of the rear weight is transferred to the front wheels. Compensation must be made for the resultant loss of weight to the rear wheels to avoid early rear wheel skid. The proportioner part of the combination valve reduces the rear brake pressure and delays the rear wheel skid.
??? wow ???
Just an FYI for everyone. I've had issues with the brake pedal going to floor and not stopping hardly. I've bled/flushed the 4 disc brakes with no better stopping power. Today I bled the power steering pump per the instructions and I can stop better now! If I double pump them its better. I'll have to bled them again later. Also, I disconnected the tag axle vacuum booster at the rear of the motor and now my vacuum gauge stays at 16 psi when I hit the brakes ( that's a later project). But if you read all of the pages in the manual it WILL fix a lot of stuff.
Indeed.. Hm?
:)ThmbUp
CircleD, any idea how much power steering fluid is needed to dump and refill the hydroboost system?
My rig sat for 2 years and it was (full) I haven't driven it but maybe a mile total for safety reasons. After I did what i did in original post it took 1.3 small bottles to get it over the full mark. I think there's an amount in one of the manuals on here from the factory. But I would say 3 small bottles at leastif drained.
DAVE will know ;). He's my hereo :D
Sorry, while they provide the information for most everything else, neither the Service Manual nor the Service Guide provide the power steering system capacity. I looked at both the capacities table and Power Steering sections.
Dave
today I was loosing power steering fluid for quite a time until I heard the power steering pump. (there I first recognized it)
Couldn't find where it was coming from and just filled it with ATF Dexron, until it was full again. Then we drove home the last 100 miles. I did check in between and the leaking stopped and the reservoir is still full.
The brakes worked fine, even a little bit better then before.
Which part of the Hydroboost and power steering system is the most likely to develop leaks ? I have to start somewhere.
Usually it will be a pressure hose from the pump to the booster or steering box. If not there check the pitman shaft on the box, That is the one coming out the bottom with the arm on it for the tie rods, the lower seal goes a lot of the times on the Saginaw boxes. Other than that maybe it overheated and blew out the top of the steering pump at the fill cap. Have to look for a concentration of fluid somewhere.
Ours developed a leak in the return line from the hydrobooster to the steering pump. It would only leak when you pressed the brake pedal and even then it was a really fine spray coming out of the hose. The only way I noticed it was the fine spots of oil down the side of the motorhome which then got me looking for the source. Rick
thanks Rick and Rick,
seems like you are right guys, just went to investigate and indeed the metal line between power steering and hydro-boost unit is very wet.
Both ends are dry, can it really be that the metal has a hole right in the middle ?
there are two lines mounted to each other, no idea which is leaking. But have probably to replace both just to get one out.
When I replaced ours, I had new hoses made and replaced the steel lines as well. I couldn't replicate the factory bends in the steel lines with the tubing tools I had, so I re-routed them to allow for easier bending. That was about 15 years ago and I haven't had to touch them since. Rick
Quotethere are two lines mounted to each other, no idea which is leaking
Vibration rubbing against each other wore a hole through.
Dave
thats a good point Dave ! thanks
So i will replace both lines. Because the second one will probably start leaking soon after I had bloody hands from changing the first one.
man there a quarter million different hydraulic lines available online. No idea, all look if the could fit but all got different dimensions lol... Is the normal Chevy dealer a good source for these parts ? Or should I get this thing to one of the RV places around ?
Would be an auto supply item not a RV place item. You can try a chevy dealer but most likely to old for them to carry anymore.
Best bet would be to take the old ones to a hydraulics shop that can make up new ones for you. Probably no more expensive than trying to fine the factory parts. Rick
i was just thinking about cutting the metal line right where the leak is and stick the whole metal line into a hydraulic hose and secure it with a couple of hose clamps.
just making the hose nice and warm, use some hydraulic fluid and it should go right over the leaking section. 2-3 inches of hose to the leak on each side should be enough to get it leak free.
this should also prevent future rubbing from the other line which is running near by
but no idea if this idea works with this limited space. because if i have to remove it, it would rather get a new part.
I replaced the pump and all the lines on my 1985 chevy chassis this past summer. Everything except a solid hard line between the brake booster and steering gear because it was perfectly solid looking. Everything was easy to get at Oreillys, and nothing was outrageously priced. :)ThmbUp
since I have to get moving at the weekend and no shop around me has the steering lines in stock
I decided to give the MH to NAPA (just over the street from my place) and let them built the steering lines.
The diagnosed that both lines are leaking: steering-pump to steering gear and steering gear to hydroboost.
Get it back today and they estimated about $250. Not to bad. If I had to do it by myself I had to buy some tools to get the nuts open and the steering-lines which are about 50-80.
not unreasonable.. hopefully near or lower than they estimated...
So I got it back. $218 in Labor and $45 in parts.
First leak:
The metal clamp which was holding both lines to the chassis caused the leak ! It rubbed through one of the metal lines. Just because it was rusty. - I think I will check the rest of the coach for such constructions..
What they did to repair it:
they cut through the metal line - like I was thinking, and installed at both sides couplings on the metal line, then they just added an adapter in between to get the required length.
Since this is a high pressure line this is probably the safest solution.
Second leak:
the line which is going to the hydroboost had have a rusted hose clamp.
I hope they did not use compression fittings on a pressure line. I have seen that done far too many times, they are not designed for hydraulic pressure and could come apart. I have seen them come apart. If it is a return line it is alright but you say it was only leaking once in a while which make me think it is a pressure line.
I'll make a picture, no idea of hydraulics. In the same line is a rubber hose with a screw hose clamp over the metal-line ? There can not be that hard of a pressure or ? It is not a brake-line.
I hope it is alright, but since I know how know the part number of this line, I can go online and look for a spare and carry it with me.
They told me what to remove to get there.
Hello, I recently bought my first rv, a 1991 Fleetwood Bounder, 31K on a chevy chassis. I have done quite a bit of looking but have not found a solution to my braking issue here on the site. I have the JF9 4wheel disc system, hydroboosted of course. I had to replace the RF caliper because of severe binding specific to that one wheel. I replaced the front pair. I did not want to pay the core charge, so I took both off and in to the store to buy the new ones. I did not get back to it for a few days.....yes, a mistake to leave the line open so long. With all put back together, I checked the MC reservoir for fluid level only to find the forward half empty. I have not found anything that addresses this amount of air in the line. I have read the entire HB section in the manuals available, an done the system bleed twice with no apparent change. I did try topping off the empty chamber first. How should I proceed? I would not be surprised by air most of the way to the calipers from the MC. Once the system is bled per the book, are the calipers bled normally like old school brakes? Thanks for any help. If there is a thread already addressing this, I could not find it but would be happy to read through it if you could point me to it.
Josh
There are several threads bit when people just put info and questions in the middle of an old topic its hard to find.
Luckily its just the front you really need to bled and not the long rear ones.
My advice is bled them test them and bled them again. Its cheap insurance to bled to much than think you're good.
But yes the new cylinders will have some air pockets that take time to bled.
Hydroboost based system bleeding is the same as a normal brake system. You can use 2 person pressure bleed, 1 person bleeder kit, gravity bleed or pressure bleed. For 1 or 2 person bleed, perform initial bleed with engine off. Then perform it once more with engine running (increases pressure at each wheel).
You said binding - One common issue is rubber brake hose failure. A piece of hose brakes loose inside the rubber hose and acts like a flapper valve. While it allows fluid to flow past the flapper when you press on the brake, it does not allow the fluid to flow back to the MC when you release the brake resulting in the caliper not releasing (brake binding).
Dave
And those hose part #s should be in Dave's Hydo Boost thread. It takes a lot of reading but you learn more than you want.
Different hoses for different applications.
Most of the Dodge info is on my website.
For Chevy, both Wagner (http://www.fme-cat.com/Application.aspx?year=1989&make=CHEVROLET&model=P30&cat=Brake&subcat=Brake%20Hoses&ga=Y) and Raybestos (http://www.raybestosbrakes.com/magnoliaPublic/home/catalog/search.html?searchCategory=Automotive%20%2F%20Light%20Truck) list the hoses (Dodge too).
If you are sure it is the front section of the master cylinder that is empty it is going to take a lot of fluid to fill those two calipers. Probably close to two quarts. The front brakes are the chamber closest to the hydrobooster and the rear are the farthest away. Even though you only did the front brakes once you get fluid to the calipers and out the bleeders it would be a good idea to bleed the rears also since this unit sounds like it has been sitting for a while. That will assure you that you have any moisture contaminated fluid out of the system. Another thing is that when you are bleeding, and yes the procedure is the same, try NOT to push the pedal all the way to the floor. On an old master cylinder the piston does not usually go very far down in the bore when working correctly. This leads to crud and rust forming in the bore closer to the bottom of the travel. Now if you push the pedal all the way down you are pushing those piston cups through all pf that crap in the bore. Sometimes it does nothing and sometimes you end up with a leaking master cylinder. I just try to err on the safe side.
Thank you guys for your ideas and help. After some more trouble shooting I discovered the right front line had collapsed internally, even though it looked fine. It blocked the line so well, that the previous owners just drove it until the all the brake material was gone and it wore most of the way through the pad backing plate! D:oH! Yikes. It's all better now, and the system bled fine, of course, once the blocked line was replaced. Am I correct in understanding that the brakes do not use the same fluid as the power steering system? I have wondered because of how the two systems appear so closely tied together. Anyway, the Hydro Boost page and your help are VERY appreciated. I am getting it ready for it's first trip with us to a family reunion in the Blackfoot area, from Mount Vernon, WA, so excited! Thanks,
Josh
Brake System Brake Fluid,
Hydroboost Unit with Powersteering, Powersteering fluid, ATF something :P
I just went through this with my 86 Chieftain. While replacing the leaking power steering lines and had the left front wheel and splash shield off, we checked the master cylinder and the rear chamber was really low as the brake feel was kind of "soft" and I double pumped brakes to stop and even the dash light started coming on. I found and bought a new reservoir thru O'reilly's for like 70.00 bucks so figured change it and won't have to deal with a 30 year old part again. Bench bled that unit and installed it and did the 2 man pump and bleed at all 4 corners and WOW, what a huge improvement !! Used brake fluid for that and GM power steering fluid for p/s reservoir but the p/s pump kept buzzing, sounded like some fords do. We then lifted the nose up and cranked the steering to full lock with engine off and let it sit for 1 hour each side, then topped off all fluids and fired it all back up to find she has that hydro-boost "hiss" sound. Working perfectly now :)clap :)ThmbUp
my power steering needed about 300 miles to get all air out. so keep checking the next couple of trips.
and check you hydroboost unit regular now, mine started leaking a couple of weeks after getting new fluids. had to replace it...
squeals a lot - as in fan belt squeal when the belt is loose from being stretched?
The power steering pump is also used to pressurize the hydroboost.
The belt is probably glazed and will not grip the pulleys.
I agree with Rick as far as the squeal is concerned.
Quoteit has plenty of fluids in it
Just curious, both sides of the master cylinder were full (you did not have to add fluid)?
I just went back a couple posts and saw the pedal to the floor post. That would not be a symptom of a slipping belt, that would be a symptom of a bad master cylinder or a broken brake line or wheel cylinder. Second Dave's question, are both sides of the master cylinder full?
The belt slipping will NOT cause the pedal to go to the floor. If the hydroboost is not working then the pedal will by high and very hard to push. If it is going to the floor then either the master cylinder went out, they do not usually just go out like that, or you have a massive amount of air in the system. IF the pedal goes to the floor and you have not had to add fluid then the only other thing it can be is the master cylinder. What you describe with the belt squealing when you hit the brake pedal tells me the hydroboost is working and the belt is bad or loose. OR, the power steering pump pulley or the crankshaft pulley are extremely worn from slipping belts. If that is the case then no matter how tight you get the belt it will slip until the offending pulleys are replaced.
You need to bench bleed the master cylinder, it will usually come with the fittings needed to do that. If you do not bench bleed it you take the chance of trapping air in it and then you will have a hell of a time bleeding it even with help. Once it is bled on the bench install it and hook up the lines and what I would do is go to the right rear and open the bleeder. Fluid should start coming out, open it a good three or four turns and then just sit there and start at it and eventually you should see a few bubbles come out followed by cleaner fluid. The rear is technically done but I always like to go do the left rear also. This one should not produce any bubbles since the main line to the rear was already bled out but you can get clean fluid through this line also. And you never know, there may have been air in there from the failed mater cylinder. Then go to the right front and do the same thing, open the bleeder until the air stops or you get clean fluid and then the left front. At that point you should have good solid brakes, assuming the master cylinder was the problem and it sounds like it is. If for some reason you still have a spongy pedal then you can either do the gravity bleed over again or get someone to push the pedal.
I just found out I have Hydrovac not Hydro boost. Big difference I guess is troubleshooting...
Helpful write-up; thank you!
I replaced my Hydroboost last weekend (the brakes would apply and not release if you depressed the pedal while turning the wheel!!!) and I'd like to add a couple notes to anyone replacing theirs: First the actual R&R is much more straight-forward than you would think at first read. Just a bunch of nuts and bolts (of which most are locking which means they fight you every turn off and on!) the large nut holding the unit to the bracket is a bear to get off, you will need to start it with a BFH and chisel especially when you forget to remove the locking ring first W% then assemble the booster with bracket to the frame just snug before final tightening so it lines up smoothly. Check the free-play of pedal to booster and booster to master cylinder before assembling so you can make corrections on the bench/ground first.
I have a 1988 Jamboree Rallye sitting on a Chevy C30 frame, and the rear brakes kept locking up on me. I replaced all hoses front and back, E-Brake cable, rear drums and shoes, front rotors, calipers and pads and also the proportioning valve. Thought it was all fixed only to find out now that the front calipers are sticking still. The driver side more so than the passenger, but none the less sticking. Could I have ruined the caliper by getting it so hot, (it actually discolored the caliper it got so hot), or could it maybe be something in the Master Cylinder? I have thoroughly bled the system and have zero air in it, so I just don't know. The Hydroboost and MC are about the only things I did not replace. Thanks for any help.
I have never seen a caliper got hot enough to discolor without burning the seals out of it. It is possible that the seals hardened but the fact that both sides are hanging and you have not replaced the master cylinder makes me think more along the lines of a bad master cylinder. Since you have already replaced 90% of the brake system it would only make sense to finish the job and do the master cylinder also. And I would replace the front calipers again if they got that hot. The hydroboost can hold the brakes on but the pedal will not be returning to the top if it is so you will know if that is happening. And if the calipers have gotten that hot be sure to flush the fluid out with fresh fluid.
Ok, found out that the MC was actually replaced, it was the Hydrobooster that had not been replaced yet. I ordered the new one and the brake pedal rod was about 2 inches shorter on the new one so looking for the right one now. Is there any adjustment built into the Hydroboost, and if so, where?
You need a gap in the rad between the booster and the master. That may have been the problem before. The gap is very small though. If you have the right master and the right booster the gap should be correct. It is possible that you do not have the right master cylinder. Who knows what happened before you got it? If you have a friendly parts store maybe they can get you the right one so you can compare the distances from flange to piston on each master cylinder. If you do in fact have the right one they can just send the new one back.
I had to reuse the pushrod from the old unit in the rebuilt hydroboost unit; the rebuild didn't come with one.
Bill
I have an issue with my 1989 Winnebago Elandan Chevy 454 unit. When I turn the steering wheel in either direction the brake pedal goes down on its own and will come back up when steering wheel is re-centered. The steering wheel is hard to turn and will only turn about quarter turn in either direction. I am in my driveway and going forward or backwards the brake stops the motor home but still hard steering. When turning the steering wheel the engine does loose rpm's. power steering fluid is full. Any thoughts. Thanks.
It sort of sounds like you have a restriction in the return line after the hydroboost but you should have two return lines, one from the steering box and one from the Hydroboost going back to separate fittings on the pump. This would normally prevent what you are describing. Could you verify that you have two returns to the steering pump? If you do you will have three lines on the pump, if you only have one return you will have two lines. The return lines are held on with a hose clamp and the pressure line is a screwed in connection.
Rick, yes i have the two return lines, one pressure line and the fill line. I guess i could remove the return line and make sure that fluid flows.
Well, it is 20 degrees out with a 40 MPH wind so I am not going out to look at my Jeep which I have put Hydroboost on but it is all out in the open so I can wrap my mind around the lines. The pressure line feeds the power steering and then goes from the steering to the brakes and then from the brakes to the return back to the pump. When using the steering the return from the steering use goes through the steering return to the pump. I am thinking there is a restriction in the return of the hydroboost that is causing a pressure back feed through the whole system. It may not be in the return line because that line is only held on with a hose clamp so if you put 1,000 lbs. of pressure on it then it will definitely pop off. I suspect there may be an issue in the hydroboost unit itself. Wait and see if Dave chimes in on this since he also has a lot of brake experience. The hydroboost replacements are not outrageously expensive but I don't feel perfectly confident to say "yes, THAT is the problem".
(https://www.classicwinnebagos.com/forum/proxy.php?request=http%3A%2F%2Fi286.photobucket.com%2Falbums%2Fll120%2FBaileyDave%2FHydroboost%2FHydroboostDiagramLg_zps65fd481d.jpg&hash=78f8013d2df87b8229e66285073b967e93f2459f)
As far as hose connection are concerned on a P30:
Pressure side: From pump to hydroboost to steering gearbox
Return side: While the picture above shows a "T" connector, there are separate return lines to the pump from steering gear and hydroboost unit on the P30 installation.
You need to use the power steering hose drawing (pdf page 75; page 6-3) in the Chevrolet Motor Home Chassis Service Guide and the power steering hose drawing (pdf page 214; page 3B3-18) of the 1980 Light Duty Truck Service manual to see the hose routing. Please note that a 454 uses the LE8 designation (Fig 3B3-42; P300 (32)). The P300 (42) chassis is the commercial chassis (breadtruck).
From page 3-5 of Chevrolet Motor Home Chassis Service Guide
HARD STEERING AT ENGINE IDLE
The P-Series motor home power steering assist system is designed for good response up to the 5,000-Ib. suspension capacity. Complaints of little or no steering assist while at idle or with the driver's foot applying the brake are usually the result of the suspension being at or very near capacity. The reason this occurs is that the Hydro-Boost system has taken some power away from the steering assist system. At this point, the power steering assist system is at borderline capacity.
This situation can be corrected by removing the pressure on the brake. This will return the necessary pressure to the steering assist system allowing proper power steering assistance. Also, if additional weight were added to the front axle there would be a momentary system stall requiring slight movement of the vehicle in order to "feel" the power steering assist system operating . GM cannot endorse overloading . To avoid problems concerning overloading, move some load rearward to remove some of the weight from the front axle. Axle weight should never exceed tire or axle capacity. Refer to the proper shop manual for the power steering pump pressure checking procedures.
NOTE :
Typical P-Series - Commercial power steering pump pressure is 1,200-1,300 PSI.
Typical P-Series - Motor home power steering pump pressure is 1,350-1,450 PSI.
In order to improve static steer effort on the P30 (motor home chassis, the steering gear has been changed on all 14,500) - 14,800-16,000 GVW chassis effective on V.I.N. N3310596. The new 710 gear ratio is 17.5:1 and the older 708 gear was 14:1 . The new 710 gear cannot be installed on the older units due to numerous changes and supports.
So my first question is, how close are you to being overloaded?
If not,
Then the spool valve in the hydroboost unit maybe sticking
Hydro-Boost Brake Systems (http://dave78chieftain.com/hydroboost_brakes.html)
or the pump may be giving up the ghost.
Concentrate on one circuit at a time:
Brake OK, Steering problem
Brake problem, steering OK
Both brake and steering problem (pump or hydroboost high pressure flow problem)
Rick/Dave, maybe what i should have asked first was, is there any brake pedal movement while steering. When I bought it I did not pay any attention to the pedal when I had been driving.
No pedal movement when steering. Now, if you are in a turn and stomp the brakes you will feel it in the steering wheel as a small jerk. It will not make you go one way or the other, it is just a sensation. I just went back and reread your original post since you ask this question. I am now beginning to think it may be the steering return that is blocked since you say you cannot turn the wheel very far before it stops. That may be feeding back pressure into the brakes OR, and I didn't think of this til now, there could be a restriction problem in the return side of the pump feeding pressure back the line of the opposing unit. The only way I know of to properly diagnose this is with pressure gauges. If you want to try to do it without it is going to get messy and semi-complicated. You will need to take the pressure line from the steering to the booster and disconnect it and connect it directly to the booster return to the pump. Basically you are taking the booster out of the circuit. Try the steering and see if it works. If it does then I would swap the return hoses on the pump and see what happens. If one is blocked it may blow one off so this is where it would be messy, have lots of speedy dry on hand. I don't think it is in the pump though, I am leaning towards the booster. The last thinking I am thinking is a blocked pressure port in the booster that would prevent fluid from the steering from getting from the steering box into the booster. That may cause your problem. I have never had that happen so I honestly do not know but I do know that the fluid has to go somewhere or things stop. This is all looking like a booster but I am not confident enough to say go buy one without personally seeing pressure gauges.
As much as I try to help people do things at home themselves this is one that you may want to consider taking to a shop unless you have the tools at home.
Sorry Rick but my research says for a stock P30 configuration:
Pressure side: From steering pump to hydro-booster to steering box.
Return side: Separate return hoses from each device back to steering pump
So, a blockage in the booster side can prevent pressurized fluid reaching the steering box.
To split the circuit, you will have to disconnect the pressure hose from the steering pump to the booster and connect it to the pressure input port on the steering box. I have no clue if the fittings are the same.
Please note I do not own a P30 rig so if anyone can confirm what I just said about hose routing it would be appreciated. Iused several different years of service manuals to deduce this.
From page 1 of this Hydroboost thread:
HYDROBOOST OPERATION
RELEASED POSITION (NO BRAKING)
ln this position, spool valve return spring holds spool valve open. In open position, spool valve provides unrestricted fluid flow between power steering pump and power steering gear. Fluid pressure is blocked from entering boost pressure chamber by lands on spool valve. As fluid pressure increases with steering demand, it has no effect on boost pressure chamber. Boost pressure chamber is vented through spool valve, to pump return port, and back to power steering pump.
BRAKING POSITION
As brake pedal is depressed, it moves pedal rod and initiates movement of spool valve. This closes fluid return port to pump from boost chamber, and admits fluid into boost chamber from pressure port. Additional valve movement restricts flow between pump and steering gear, causing pump to increase fluid pressure to maintain flow rate to steering gear. As fluid pressure increases in boost chamber, it forces piston forward actuating master cylinder piston, resulting in brake application. lf fluid pressure is required for steering while braking, pump pressure will rise and spool valve will shift in an open direction allowing more fluid to flow to steering gear.
Thanks Dave, That is why I was hoping you would chime in. I am going to go look at my Jeep setup tomorrow and try to think of some scenarios but really this is a problem that needs to be checked with the proper gauges. You are working with between 1,000 and 1,300 lbs. of hydraulic pressure and you do not want that blowing up in your face.
Regarding the flow of pressurized fluid from the pump through the hydroboost unit to the steering gear, here is a good description of how it flows through the hydroboost unit http://www.brakeandfrontend.com/operation-diagnosis-and-repair-of-hydro-boost-power-assist-systems/ (http://www.brakeandfrontend.com/operation-diagnosis-and-repair-of-hydro-boost-power-assist-systems/)
It also has a lot of troubleshooting information.
Rick / Dave, Thank you for the time in answering the questions. The last post from Dave was great. I will start with the return line. Then check brake fluid movement, Then flush and retest. After I get this taken care of, I will start on the great "why my electric fuel pump is not working". Having fun as always.
Thanks,
Guys
HELLO! :)
I have a 1990 coachmen SB270 A class on a chevy chassis.49k miles on the old 454 with the 3 speed transmission. TBI gets me about 10 mpg, not so bad for hauling 5 plus tons down the road, all I need to do is stop 5 plus tons.
This is where my current set of issues are. I replaced the power booster(brand new unit) and did not install the push rod the first time(my bad but have it installed now). I filled up the reservoir, cranked it a few times, check the level it was to much so I removed some of it to the proper level. Then I started it and now the brake pedal goes down to the floor(almost all the way) when the motor runs, I shut off the motor and the brake pedal returns to the full unladen position. I tried to bleed the air out of the system by pumping the brake pedal 4-5 times with the engine off, still no change(pedal to the floor with motor running.
So If i may ask a greenhorn question, and that is ,what is causing this to happen? My thoughts are that there is excessive pressure/vacuum causing the pedal to go to the floor w/motor running.
No leaks of any kind but I did notice that the booster/steering pump gets very hot after about 3 min run time.
Any ideas or thoughts would be very helpful.
I would like to thank you in advance for any and all help!
We are trying to get to upstate New York next week and this kinda puts things on hold till the issues is resolved.
Cheers
rvers
All the booster does is adds power to the rod going to the master cylinder. If the pedal is going to the floor then either the rod you put in is wrong or the master cylinder is bad or there is no fluid in your brake lines. The pedal should be hard to push once you bleed off the accumulator charge which take about three pushes of the pedal under normal use. with no power the pedal should be hard and high but if you can still push it to the floor with some effort then the rod or main brake system is at fault, not the booster. There is a mechanical connection from the pedal to the master cylinder is case of booster failure.
All the booster does is adds power to the rod going to the master cylinder. ok got it now what part of the system tells it to depress or return? Is that the power valve?
I used the old push rod as per the manufactures install data.
My pedal bleeds off fine and get hard and high with engine off.
something it telling the booster to apply pressure to the rod(power valve?) when the engine is running and not allowing it to return to normal operating conditions is my thinking as of now.
I have read the 3 pages here on the hydro boost issues and so far nobody has the pedal to the floor with engine running issue.
Can a loose belt or a blocked return line cause this issue? I will be checking them tomorrow.
I would now like to thank you for both your time and knowledge Rick and perhaps we can crack this nut together( with a little help from our friends here)
Cheers
rvers
And here is Hydroboost information: http://dave78chieftain.com/hydroboost_brakes.html (http://dave78chieftain.com/hydroboost_brakes.html)
Dave, Nice name, as it turns out I too am a "Dave" lol.
Thank you for correcting my post :)clap not sure what happened there
Thanks for the info :)ThmbUp and the links but as it is they are not helpful at all regarding my issues. I have read and read and read and still there is no mention of the brake pedal moving towards the floor(moves about 1/2-3/4 of the way down when the engine is started). All fluids are full and new. I installed a brand new hydro unit,filled the steering fluid, bleed the lines of air by turning the wheel. I also released the reserve pressure via the pedal with the engine off. I have tried everything mention in the posts and still no change in the pedal movement.
Now if I may ask the following questions please ;)
1, What provides the power to the spool valve to operate it?
2. What then tells the spool valve to apply pressure to the brake push rod?
3, What then tell the spool valve to release the brake pressure?
For some reason the brakes are being applied all the way when the engine is started via the spool valve,push rod. So I am thinking now that perhaps I got a bad unit and need to return it?
Have a great day folks!
Cheers
rvers
Does this help?
http://www.brakeandfrontend.com/operation-diagnosis-and-repair-of-hydro-boost-power-assist-systems/ (http://www.brakeandfrontend.com/operation-diagnosis-and-repair-of-hydro-boost-power-assist-systems/)
Best I can offer this morning. Off to work - Later
Sounds to me like you have a brake system issue not a booster issue., it is pushing the master cylinder all the way down which means the problem is beyond the booster. Look in the top of the master cylinder if you can while pushing the pedal down and if the fluid is moving around then the booster is working fine, the problem is in the brakes.
QuoteI have read and read and read and still there is no mention of the brake pedal moving towards the floor(moves about 1/2-3/4 of the way down when the engine is started).
Please read the HYDROBOOST FUNCTIONAL TEST section (top left) on page 10-24 (pdf page 2) of Hydroboost Description and Repair (http://dave78chieftain.com/hydroboost_brakes/HydroboostDescandRepair.pdf) (was a link at the bottom of my page). If that test passes (no fluid in accumulator), then I think you are OK. I suspect the drop your experiencing with accumulator full is the same thing. In other words "The sinking of the pedal when the engine was started is a result of the power chamber being pressurized." as described in the Pedal Feel section of http://www.brakeandfrontend.com/operation-diagnosis-and-repair-of-hydro-boost-power-assist-systems/ (http://www.brakeandfrontend.com/operation-diagnosis-and-repair-of-hydro-boost-power-assist-systems/)
Dave with all do respect i have read and tested all that I could. I now know how it all works and have come to the conclusion that the unit itself is faulty. I have great fluid flow from the pump steering box and the return line. I pulled the return line and found it flowing out with fluid from the pump. I then started the engine and there was fluid coming out of the return port. It has to be a stuck spool valve that is only letting the fluid to activate the push rod and not allowing it to power chamber to depressurize(weak return spring is my call), that does happen(pedal comes up) when I shut off the motor tho. The tolerances are so close between the spool valve and the chamber that a weak spring may be all it takes
I removed the MC, all full with fluid and I do have fluid movement while pressing the pedal with the engine off. no signs of any leaks in the lines or at the valves I also have the power reserve working as per the three pushes of the pedal with each push requiring more pressure and less movement. I am pulling the unit tomorrow morning and returning it for another one. I will update ASAP.
Again I do appreciate all you time and efforts and most of all your patience in dealing with a greenhorn!!!
THANK YOU! :)ThmbUp
Cheers
rvers
I understand what you are saying. Hope the new unit solves the problem.
Hydroboost can be a pain, I am going through that right now with my 98 Dodge diesel dually. Slow pedal return was hanging the front brakes on and smoked the pads on a busy interstate with a full load and full trailer. Not fun. On my second unit now with same symptoms, they can be frustrating.
3/3/18
Can we update the photo's....thanks
Since we are at it,
I own a 1975 2900 chevy sportscoach.
The hydroboost is leaking from the front,
Pipes and connections are dry.
Can't find any replacement or rebuild.
Any suggestions?
Thx
Give Geoff at Alretta Truck Parts a call.
http://www.alretta.com/ (http://www.alretta.com/)
Thx
Will send them a mail!!!
Cardone Part # 52-7249 (https://www.cardone.com/search?criteria=%22%22&caryear=1975&carmake=Chevrolet&carmodel=P30&carparttype=Power%20Brake%20Booster&ymmsearch=true&carengine=null)
Google (https://www.google.com/search?rlz=1C1CHBD_enUS765US770&sxsrf=ALeKk02TljhMyMORKl4Q8bOX2wZMHSg6aw%3A1594071590786&ei=JpoDX4qyL-WEytMP5uGE6A0&q=Cardone+Part+%23+52-7249&oq=Cardone+Part+%23+52-7249&gs_lcp=CgZwc3ktYWIQA1Di3xlY4t8ZYP3sGWgAcAB4AIABjQGIAY0BkgEDMC4xmAEAoAECoAEBqgEHZ3dzLXdpeg&sclient=psy-ab&ved=0ahUKEwiK3ai3y7nqAhVlgnIEHeYwAd0Q4dUDCAw&uact=5)