Hydroboost Upgrade considerations - Information collection.

Started by eXodus, December 21, 2021, 06:05 AM

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After my P30 Hydroboost started leaking I went down a rabbit hole of Hydroboost research.


1. there are no new Hydroboost being made anymore for the P30 application.  Only rebuild available.
2. you can rebuild the Power Piston Cylinder of a Hydroboost with a Seal Kit - but difficult to address the spool valve.

I got myself a rebuild unit - but that one blew out the accumulator, after I spend 4 hours installing it...
Many comments in the Facebook section said similar things that their rebuild units failed in rather short time frames or never worked out of the box.

3. A P30 is a GM product, for better or worse, GM is very thrifty and reuses bolt patterns and parts for at least 50 years.
4. P30 has 4 different Hydroboost versions over the years.  Dual Valve and Single Valve.  Golden Accumulator and Blue accumulator
5. Gold Accumulator is for rear drum brakes and charged at 350PSI Nitrogen
6. Blue Accumulator is for rear disc brakes and charged at 450PSI Nitrogen
7. Very early versions have a Spring loaded Accumulator
8. Power Steering Pump for Hydroboost runs at 1500-1600PSI
9. 1999 or so GM sold the P30 division to Workhorse, They kept improving and making the P30/P32 (wide front track) chassis to about 2005
10. Almost all improved parts from the Workhorse fit to the classic P30
At this point I found this video:

It explains how to fit a new 2012 or later AC Delco Hydroboost to P32.   
11. About in 2003 GM changed the Hydroboost with the arrival of the LS engine - they increase the Diameter of the Power Piston slightly up.
12. In 2012 with the Duramax LML introduction a GCWR of 35.000 LBS of those trucks - GM improved all internals of the Hydroboost
13. Many Pickup owners of the are switching to the new Hydroboost - it's a very common swap:
14. The new AC Delco 178-1036 unit looks strikingly similar to the P30 ones.  GM Genuine Parts 178-1036

And it's cheap as a rebuild one around $200 - Amazon or Rock Auto has them.

So the guy on Youtube used a different AC Delco new part - but he had to change out the push-rod - which seems like a lot of work and potential for messing up the unit.
While the LML Hydroboost - looks like a pretty good match. All the lines are in the right spot and should just bolt in.

A few things I don't know yet:
Pushrod length? - makes a difference in paddle position (brake switch) and travel.
What is the new accumulator charged with? 450PSI? 350?  something even higher?  What difference does it make?

As far as I understood - the accumulator is for emergency braking, it gives you 3-4 good brakes with the engine off.
Why did the drum brakes get less pressure? I know drum brakes need less force to actuate.  But braking in the P30 with drums is not great, why the lower pressure?

I'm at the point of probably just ordering the new Part and put it side by side on my Bench with the old one and check out all details.
Anything you guys could see potential going wrong?

I'm just drawn to a better braking performance with a factory new designed part. Instead of scraping by with remanufactured ones, which are only getting worse when they go through the cycle a second or third time.  My last remanufactured exploded - the accumulator broke out of the housing. Pretty dangerous, lost all power steering fluid in an instant.

Eyez Open

I may well go down that rabbit hole. What I need is to have that new booster and my current setup side by side and see it live. What keeps me from just leaping in is the time and labor...it would be a lot of time invested and little return on braking improvement


 actually, the new units have from what I understand much.better braking support through the larger bore piston. From 22.000lbs GCWR to 35.000lbs, sure there are many more parts to the braking system aside the booster. But gives me some confidence that they are better.

While changing my hydro boost twice last week I found a few important time improvement to the procedure.

First. Remove the metal shield in the wheel well.  It's only a few bolts. Many a working from below.
Second, get battery power ratchet or a air ratchet 3/8 (Saves an hour and lots of  $@!#@!)
Third, tie the master brake cylinder with a cable against the frame up.
Remove both bolts of the brake paddle linkage at the front of the hydro boost.  The manual calls for only on of them at the bell crank.

With this modification to the process you can lift the hydro boost up and forward to separate from the brake cylinder.   

No need to bleed the brakes anymore.  Saves at least a couple of hours.  The second time I was done in less then 3 hours.

I guess a skilled mechanic on a lift could do it in about 2 hours labor.


After my resealed Hydroboost started leaking - only two months after putting everything back together. I just ordered the new version of the Hydroboost. GM Genuine Parts 178-1036

I took a ton of pictures and measurements the last time I had it out. There are various ways to adjust the position of the Hydroboost to accommodate for a longer rod.
The only problem would be a shorter push rod.

The new hydroboost has a larger reservoir according to other discussion boards- but that should only impact emergency braking with engine off. 


Got the new one in.

Looks promising.
1986 - 2003 Old Hydroboost Rod:

New Hydroboost (2012 and up GM Genuine Parts 178-1036:

The hole size are looking identical - have to verify with the bolt - (which is still on the RV)

The length is slightly different (1/8 to 1/16)  but that could be a measurement error of mine - the "nose" of the new hydroboost is shaped differently then when I took the old measurements. So the reference point might be a bit down. And I used a different tape measure and the camera angle is off. So they could be identical in length, but I need to take them of the RV to know exactly.

But even with that - that shouldn't change geometry or brake paddle travel by much.


1969 D22, 2 x 1974 D24 Indians, 1977 27' Itasca


I was able to fit the ACDelco 178-1036. It's an almost a bolt in replacement. There are two differences

1. The push rod hole is about 1mm  1/16 too large for the bolt on the P30 - I've just wrapped a few layers of metal flashing around the bolt to make it a flush sit
2. the rod is slightly shorter, as I guessed with my initial measurements. Which means that the brake pedal sits a tad lower - (adjusting the brake light switch - disconnect the cables and screw it inwards) .

Otherwise - not even the push rod for the brake booster needs to come out - has the same exact length. The first test drive around the block was a great success - the brakes feel much better - stuff was flying forward :P will test drive the next days more extensively and follow up with pictures.


First - you need to get the new Hydroboost out of the adapter plate it came with:

After many trials and error I figured that putting the Square Nut into a Vise and turning the Hydroboost with a Breaker bar at the bolts at the back was the way to go:

That is how the new one looks:

The Cylinder of the new Hydroboost is 46mm vs the old 41mm  - that means the area of for hydraulic to act on goes from 1269mm2  to 1662mm2  - which is about 1/4 or 24%  more Power  :D

Here the new pushrod - with the old bolt:

so there is a small gap around the bolt. But it has the same width as the old one.

So I made myself a sleeve out of some galvanized flashing I had laying around.

Wound it around the bolt and then inserted it into opening of the rod - in there - it flipped open and stayed.  Nice for mounting underneath.

The bolt turns nicely in the sleeve - will see how good it will hold up - that's something I can upgrade later - you can access if without taking out the Hydroboost itself.
Perfect would be a machined brass insert - but the material is not very thick.


I found this nice picture of the p30 P32 brake linkage.

The push rod of the AC Delco 178-1036 is slightly shorter, which means that the vertical rod sits a bit higher.

The Brake-Paddle position can be adjusted by moving the bracket down as far as possible in it's screw holes. 
If the it's still to far up - I would assume by drilling out the bracket holes just a bit - would be possible to get even closer to the original position.

Another installation help:

After removing the shield in wheel well - tying up the Master brake cylinder - saves the hassle of bleeding the brake system.
Tie up it up with a wire - unscrew the master from the Hydroboost -  then unscrew the hydroboost from the linkage and frame

Lift the Hydroboost up and forward - away from the Master Cylinder - then you can easy wiggle it out without opening the brake system.


1000 Miles later with the new Hydroboost: 

This is really the best brake upgrade for the P30 - it is sooo much easier to get the large RV to stop.  It's actually on almost effortless side, braking doesn't feel like a large vehicle anymore.
I actually have to brake careful since all the stuff in the cabinets comes rushing forward.  It's easy to control after you get used to the higher boost level, so no worries about tires locking up.

With my 5000lbs trailer in tow and the rig full loaded up @ 11000lbs Totaling at 16000lbs (still 3000lbs short of GCWR of 19.000lbs)  it now feels like I actually got control. Before this upgrade I always left a huge distance to the car in front of me because I wasn't sure I could stop.

At this point I can absolutely recommend researching if this upgrade is suitable for any P30.  The new ACDelco part is a new, improved - and not remanufactured and is designed to stop a much larger and heavier vehicle.

The install is straight forward - only minimal adaption work required:
1. Sleeve for the rod
2. drilling the bracket holes a bit large so that it can sit 1/4 inch lower


1969 D22, 2 x 1974 D24 Indians, 1977 27' Itasca


First let me commend you on a well written and very informative post. Often the intent to educate is there but the post is poorly written, so its helpfulness is hindered by wondering if the poster meant "this or that?" Things like including links are so valuable to someone who is seeking to solve an issue also. Thank you for expending the effort to include this type of information.

I don't even own a rig that has this type of brake system in it. I'm always interested in learning about stuff especially related to brakes and suspension. At one time I owned a tire store and our repair focus was on brakes and suspension. My tire store mainly catered to passenger and light commercial vehicles with an occasional RV getting brake work done by me.
I had my business in the 1980's thru the beginning of 1990. I started my career by working for independent tire shops that had multiple locations in the San Diego area in the late 1970's. My brake work experience back then mostly involved replacement of friction and the basic hydraulic parts that operated the friction parts (friction = brake shoes or disc brake pads and brake drums or brake rotors Hydraulics = wheel cylinders, disc brake calipers and things like a master cylinder every so often.

I never had any experience doing brakes on a hydroboost or hydovac system for an RV....I have been involved with a few for lighter trucks and a few GM passenger cars that had other than a conventional diaphragm type of power brake unit but I only can recall managing a handful of repairs that involved those hydro type systems so I am certainly not very knowledgeable there.

My only wonder after seeing what you have accomplished.....Do you have concerns that other components in your system may not be able to handle added pressure that incorporating a hydroboost  made for a bigger truck offers?

Also have "Ethyl" 1955 Ford C600 equipped as a rolling tool store(ETTT)."Brutus" 1972 Ford F250 60k original miles. "Panzer" 1976 MBZ 450SL Roadster.


This is a valid concern and I appreciate you stating it.
Took me a while to understand what the Hydroboost is doing.  It essence it increase the force (not necessary pressure) which is coming from the brake pedal.
I strong person might be able to push the brake pedal with 300lbs in a emergency.

Any brake booster multiplies that force - A regular vacuum boost maybe does 3-5x  - they Hydroboost does a 5-8x.

A few stats: Regular rubber brake lines (probably the weakest link to be concerned about) are usually rated for 4000-5000psi for regular operating and 7000Psi for burst.
Metal brake lines in the order from 5000PSI up to 15000PSI
From a pure number perspective if looks like if the brake system could handle the added force.

What do consider - we are talking about old RVs - so parts are potentially old. You can get leaky brake lines or other parts even without upgrading anything in the system.
So to do this - your system has to be in top shape.

Like with anything brake / safety related, if you don't know what you are doing - ask a professional to do the job.  This here is informative only, since the P30 community is running out of options due to the age of available spare parts.

Here is the story I stumbled over when I was doing the research for this part:

GM is producing this identical Hydroboost since the forever-  but in 2004 there had been enough accidents due to accumulator blowing out that there was a recall.  At that point GM redesign that thing.
"Product Safety - Hydro-Boost Accumulator Over-Pressurization #05006 - (Mar 23, 2005)
05006 -- Hydro-Boost® Accumulator Over-Pressurization"

It took a few years and in 2011 the new design (the one which I'm using) started to being put on new GM HD products.


Any updates to this mod?  I'm going to talk to my mechanic about it.  I wonder if LocTite QuickMetal would work instead of metal flashing.


I've been poking around on other forums, and a guy on irv2 recommended a newer part, GM 178-1040, that he says is easier to replace the push rod on.  It looks to be a little cheaper too. I'm hoping the original poster will come on here with his opinion.


I am still happy with the GM Diesel pickup hydro boost I put in 2 years ago, no leaks the system works great.

 Acdelco 178-1036  GM Genuine Parts 178-1036

No pushrod to change. It bolts right in.

The only mod you need to do is fabrication that little sleeve around the pin which goes through the pushrod.

So far I have not seen wear on the metal flashing I put in.

The 1040 you posted looks very similar. Not sure if you have to change the pushrod.  I was hesitant about that since there is a lot of force on that piece

I had pictures uploaded here but they vanished.  I try to find them.

Braking is sooo much better:) Pedal feels like a regular Pickup now. It slows down like a Pickup.