New to list in New Mexico

[Oz]

Thanks for sharing this with us.  If we were to write a book of "short stories" documenting the shakedown trips of newly purchased, vintage RVs, it's contents would far exceed the length of the Ecyclopedia Brittanica and it would be far more intersting!

I'll pass on making any puns on the location of your mishap.  It's good to see you have a positive attitude and understand "the nature of the beast" quite well.  The broken brake pedal return spring problem has been an experience I recall hearing here a few times.  Interesting how a new problem shed light on the previous one!

I hope you're on your way very soon and that this is the last of the challenges you have on your trip home!

[awatters]

Mark - puns are no problem.  I'm always saying that I am going down to Lost Causes to work on the Winnebago.

Dave - My apologies, I got your email but with work and other issues I forgot to reply.  It is the system shown on the M375 (late) page with the dual Bendix Hydro-Vac Boosters.

I was planning on going down this Friday to get the starter back in and see if the brake return spring solves the problem but work says I have to be available and able to log on in case we have problems with our data conversion test.  Told them I could delay until the following Friday.

[DaveVA78Chieftain]

The booster hang up issue can apply to the Hydro-vac also however that would apply to both wheels on a given axle.  The rear booster is for the rear axle.  There are Master Cylinder P/N's on my web site.

Dave

[DaveVA78Chieftain]

Al,
The M375 (late) configuration is split into Front and Rear systems.

http://i286.photobucket.com/albums/ll120/BaileyDave/Dodge%20Brakes/M375Late.jpg

http://i286.photobucket.com/albums/ll120/BaileyDave/Dodge%20Brakes/HydrovacCircuit.jpg

The only place the front and systems actually come together is at the Master Cylinder and the Combination Valve.  The only thing the Combination Valve is used for is to compare the pressure in the front system to the pressure in the rear system.  A piston moves back and forth looking for equal balance between the 2 systems.  The hydraulics for each system remain seperate from each other with the only output being to turn on the Brake light if there is an imbalance between systems (piston is forced left or right).  As such I feel you can rule it out as a potential problem.  The only common point between the front and rear systems is the Master Cylinder.

Given that this is only a brake system staing on issue, my question is:
Does this problem affect both the front and rear system?
(Are both front and rear wheels locked up?)

If Yes, then the Master Cylinder is the problem.  I suppose it could be a pedal spring but those springs are only used for the pedal mechanism.  The only way the missing pedal spring could be a problem is if the pedal mechanism itself was hanging up.

If only Rear, then either:
1) The rubber hose between rear axle and frame is defective.  A piece of rubber has come loose inside the hose and is acting like a flap valve.  When you release pressure at a wheel cylinder the flap comes back up.  Basically it acts like a check valve.
2) The Control Body in the Rear Hydro-Vac Booster is binding up.  The booster is somewhat like a master cylinder.  It senses the hydralic force from the Master Cylinder and then multiplies that force using the large vacuum bladder.  When line pressure is increased from the master cylinder (pedal pushed) some hydralic fluid is directed to the wheel cylinder however the booster control valve also sees the increase.  A check ball blocks the master cylinder line off and the control valve directs vacuum to one side of the bladder with outside air pressure being placed on the opposite side of the bladder.  The bladder pushes against the booster slave cylinder piston therby multiplying the hydraulic force being applied to the wheel cylinder.  When you release the brake pedal, springs inside the master cylinder push the piston back to it's "home" position reducing line pressure.  The booster control valve senses this pressure reduction and redirects outside air pressure to the vacuum side of the bladder releasing line pressure to the wheel cylinders.   If the booster control valve is hanging up and not reacting to the line pressure reduction from the master cylinder then the brakes in that system will not be released.

If only one front wheel, then:
1) The rubber hose between front wheel and frame is defective.  A piece of rubber has come loose inside the hose and is acting like a flap valve.  When you release pressure at a wheel cylinder the flap comes back up.  Basically it acts like a check valve.

If both front wheels, then:
1) The Control Body in the Rear Hydro-Vac Booster is binding up.  Refer to the write up above for the Rear Booster.

I realise this may sound overly simple but in actuality it is.  It is a matter of divide and concur based on all the symptoms being presented.

The later disc brake systems work exactly the same way.  They however have a proportion valve added in order to delay the disc caliper response  in order to allow the hydraulic pressure to overcome the spring force applied across the rear wheel cylinders.

There is an extensive write up on my web site about Hydro-vac booster operation (including an old army video).  While the mechanical design has changed over the years, the principle of Hydro-Vac operation is the same.
http://dave78chieftain.zxq.net/HydroVac_brakes.html
Dave

[awatters]

It's been a while since I updated this thread.  So much gets in the way when you have to dedicate 6 hours of round trip travel to go work on something for a few hours.  i??

Our 1 year anniversary as owners of the Winnebago Indian was last Monday and she is still sitting in Las Cruces.     Not for lack of trying though, I keep telling my wife that the old girl is just afraid to go to a new home.    The good news is I have found an auto transport broker that also handles transporting RV's and we are only looking at about $500 to have her brought here.    Just wish I had talked to them a year ago.  D:oH! 

I drove down yesterday and got her turned around so she can be loaded on the lowboy trailer.  Since she had been sitting since last fall so it took a couple of hours to get her running.  I think our mascot for this vehicle is going to be a mule because she is stubborn beyond belief.

Now I just have to wait for a phone call from the broker saying she has someone lined up. 

[JDxeper]

You can call her Jenny but not Jacka**.

[awatters]

I think we now have a name for her.

Thanks JD.