Help needed with '74 Dodge motorhome

[HGDMARTN]

I have an antique motorhome built on a 74 Dodge 1 ton (P30?)chassis. Due to some bad experiences, I have not driven it any in 2 years. But, last year I did alot of work including total rebuild of the front brakes because of my problem. Here it is: It has air assisted front disc and rear drum brakes and sometimes the front brakes will not release. It was so bad one time 2 years ago that I drove it across a gravel lot with the front wheels locked up. Parked it for a while and they unlocked and I drove home. I figured it was due to rust not allowing the calipers to slide, so last year I rebuilt including new seals, pads, fluid, and turning the rotors. Then parked it for a year. Took it out today as it seemed OK around the driveway, no sign of any problem. Got 2 miles up the road and smoke pouring out of both front brakes. Got it back home, jacked it up and both front wheels locked up. Let it set a while and they both freed up. Not free spinning like I would like but free enough to turn with one hand. Took it out again and same thing. Ran pedal to the metal to get home at 30 MPH. I took one caliper off and it appears the piston will not retract for some reason. I had to open the bleed screw to retract the piston enough to re-mount it. A large C-clamp would not budge it. I did not try the other side, I assume the same thing.

What could be wrong? The rubber lines look corroded, but being both brakes I would not suspect an internal collapsed line. There is not much there to go bad; a master cylinder, a booster, a distributing valve, and then it goes to the wheels. Any of you experts got any ideas? I have to have this ready to roll for a Thanksgiving vacation.



Thanks in advance.

David



BTW - Wife will be driving the Cummins along side me in case something does tear up.

 

[Doc Tinker]

Sounds like a bad master cylinder, or moisture in the fluid.



Doc

 

[Little Bill]

I've had similar problems with 2 70's farm trucks in the last 2 years. Both cases it was a collapsed rubber line where the line passed through a steel frame clamp. The build up of rust from the inside of the clamp and the hose was enough to collapse it enough that high pressure fluid from master good get through but could not back out when pedal was released.

 

[Jumbo Jet]

I had the same problem with an '83 motorhome. Replaced caliper etc.



Finally fixed the problem by replacing the rubber hose. Brake man told me to check that and he was right.

 

[B.G. Smith]

Dodge MH

David, on the Dodge trucks of that vintage, the front calipers came with plastic pistons in the calipers. They were notorious for locking up, had to be replaced with cast iron pistons. If yours atre still plastic, that is your problem. bg

 

[TowPro]

Re: Dodge MH

I agree about the calipers. I read you replaced the seals, but not the pistons?



Also unless you flushed the brake system 2 years ago when you did it the last time, that old fluid would be in there still, causing your corrosion problems. See Brake fluid adsorbs water, which causes corrosion.



I would replace the calipers with rebuilt units, and as others are saying, replace the brake hoses. If there original hoses, there overdue anyway.



What ever you do, when you bleed the system, suck the brake fluid out of the master cylinder, refill it with fresh, then start bleeding until the fluid is clear coming out. No need to send all that old contaminated fluid through the brake system.



Also its been sitting so long, I would at least make sure the star adjusters on the rear brakes are not stuck. . Might as well pull the drum to check the rear wheel cylinder's and axle seals.



While your looking at hoses, keep in mind there is another rubber hose for the brakes back by the rear diff.



Something else these older dodges had problems with, the Ballist Resister. Its a white looking block mounted on the firewall with wires attached to both ends. What it does is change 12v to around 8v so your ignition coil will not over heat. When your in "crank" mode, you will have a direct 12V to the coil, when in run mode, the electric is routed through this resistor. They do go bad, and there cheep, replace it now or later. The symptom will be you crank the engine, it starts, but stalls as soon as your release the key.



Hope this helps.

 

[HGDMARTN]

Wow, I always appreciate the excellent knowledge available on this board. Thank you all so much. Here is more information:



The pistons are the steel type.

I was sort of shying away from the collapsed rubber lines since both front wheels will not release. It would be somewhat of a coincidence for both to fail I would think. Nevertheless, I am going to pull them right now to have 2 new ones made tomorrow. Dodge dealer can not go back before 1984 to get parts. He He NAPA can not get them either

Master cylinder was new 3 years ago before I got it. I hate to think it has failed, but setting that long can not be good for anything.

How about the proportioning valve? Is there anything in there that can be keeping the fluid from flowing back through the lines?

Oh yeah, why would the thing appear to be perfectly OK around the driveway and then go to pot when I hit the road? Could heat be affecting anything to cause this?

I am going out now to look for more.

Keep the info coming. You all are GREAT.



Thanks.



Oh yeah. The ballast resistor. The good ole ballast resistor. I found that one out the hard way. Now I have 2 spares that I carry with me just in case. Sounds like you have travelled that same route. Thanks for the heads up.



David

 

[TowPro]

Heat is the answer. Even when they are cold they are still partially frozen, causing the brake pads to ride on the rotors and cause heat. The hotter it gets, the piston expands and sticks harder, causing even more heat, until you get to the point that it sticks and you can't move.

Originally posted by HGDMARTN



Oh yeah, why would the thing appear to be perfectly OK around the driveway and then go to pot when I hit the road? Could heat be affecting anything to cause this?

David

 

[HGDMARTN]

Thanks to all of you for your excellent input. You were all right on the money. I knew I had a real problem when I pulled the caliper lines and not a drop of fluid drained from the master cylinder. So, I kept digging and found the master gunked up with moisture and rust. I replaced it all except for the steel lines and the proportioning valve. Flex lines were not available, but I found some similar with the banjo end and all I had to do was enlarge the hole and grind the corner to make it fit... safely. I really was a little scared having never done much brake work before, but it all turned out to be fairly straight forward. Also found that it had wrong master cylinder. I put correct one on and drained and replaced all fluid and now she stops like she should. I am getting very excited about my new 30 year old toy!



Thanks again for all of your help. This site has saved me so much money over the last 3 years!



Thanks,

David