brakes seizing up on older motorhome.

[Islandtime]

We have replaced all calipers, flexible hoses, master cylinder, and power assist booster on our 1985 Class A P30 Chevy chassis motorhome. After traveling 2 to 3 miles, the travel on the brake pedal becomes less and less, until there is no travel left and the brakes are seized up.

I am at a lose for the cause of this, as everything is now new. Any suggestions as to what could be causing the brakes to seize??

[Robagedon]

I had same problem on a 1984 chevy p30 rv. The soft brake line mount that bolts to the frame ends up pinching the line due to rust. Uncrimped the clamp and blew air through the line air flowed freely fixed the brakes locking up

[way2roll]

While I am sure the OP would find this information helpful, you are responding to a post that's 9 years old and the OP never returned to the conversation. 

[rgatijnet1]

donfrump wrote:

sjholt wrote:
I think the problem may be in the brake crossbar binding up and not releasing the brake. That happened to my 86 P-30.
I drilled a 1/8 in hole in it and stuck a zerk in it and pumped it full of grease. End of problem.
Worth looking at.

Are you talking about the brake peddle assembly?

There was a problem with that happening on some early WH "W" chassis models to lubricate the bellcrank. You just drilled a hole and added the zerk. I was not aware of that being a problem on the "P" chassis.

[Tinstar]

I replaced the two rear brake calipers last summer. I went to a truck supply place to buy them. I asked if they were rebuilt. The staff said they used to rebuild them but have never had good luck and only sell new now because of the rebuilt failures.

I got rebuilt ones just a couple of years earlier and they didn't last at all. Mine were burning the brake pads up in a lot of stop and go traffic.

Make sure the slides are well greased.

[donfrump]

sjholt wrote:
I think the problem may be in the brake crossbar binding up and not releasing the brake. That happened to my 86 P-30.
I drilled a 1/8 in hole in it and stuck a zerk in it and pumped it full of grease. End of problem.
Worth looking at.

Are you talking about the brake peddle assembly?

[sjholt]

I think the problem may be in the brake crossbar binding up and not releasing the brake. That happened to my 86 P-30.
I drilled a 1/8 in hole in it and stuck a zerk in it and pumped it full of grease. End of problem.
Worth looking at.

[fischer]

found a fix posted by jdrocci
1 loosen the bolts holding the MC to the booster insert flat washer. between the two assembles as shims
2 he noticed that the brake pedal linkage seemed to be preloading the booster rod a bit, he adjusted it a couple of turns until there was noticble slack
3 his pedal rising was cured and no lock up
4 his problem started after replacing the MC good luck
5 I think he took the shims back out after fixing rh problem

[donfrump]

jplante4 wrote:

donfrump wrote:
there are no "cylinders" to hone out on disc brakes

Ok. I'm willing to bet that I was working on brakes before you were born...

Have rebuilt tons of calipers and have cleaned/scotch brighted/glass beaded them but never honed as the piston is not a tight fit. Have replaced lots of pistons with new ones etc.I have never honed like a wheel cylinder however? I guess u could hone them? just never did it that way.MY point was a wheel cylinder has to be honed so the rubber cups have a clean non porous finish to seal against.Calipers don't work that way as the piston simply seals against the thin rubber sealing ring.But then I will assume you know that already.
So I concede you could hone them ? but why? there is no precision fit of rubber to surface as a wheel cylinder requires.
back in the old days we used to have oversize cups in stock in case we had to hone too much for a clean seal surface.Calpers don't require that

[jplante4]

donfrump wrote:
there are no "cylinders" to hone out on disc brakes

Ok. I'm willing to bet that I was working on brakes before you were born...

[Rickieblue]

Another possibility is that the brake lines were put on the master wrong as the rear brakes have a residual valve which holds 10 to 15 psi in the system whereby the springs on the rear shoes require more than 15 psi to activate but the front will drag pretty heavy with 10 or 15 psi in the system. Also the master could have had the residual valve put in the wrong outlet too!! Just another option to look at.

[fischer]

I remember that certain brake pads can swell after heating up . I don't remember what kind.

[wrgrs50s]

I recently had a master cylinder go bad and it was locking all my brakes on my 2006 Silverado in exactly the same way. It's possible that the master cylinder, although new is defective. There's a proper sequence to bench bleeding the master cylinder, being careful not to push the plunger in too far which can cause damage to a new master cylinder causing it to stick in the compressed position. Also there is an adjustment rod that pushes in the master cylinder at the booster that some times requires adjustment to achieve the proper amount of slack.

It's not likely that this happened but another mistake some people make is putting power steering fluid in the reservoir instead of the proper brake fluid. It looks clear like brake fluid but will swell all the rubber components and end up locking your brakes.

It's not likely it has anything to do with the calipers unless you find it is only locking up on one wheel.

[donfrump]

jplante4 wrote:
The brake pads have to move freely on the pins holding them in, and the caliper needs to retract slightly after the pressure is released. I'd start by pulling each pin, wire brush the rust off and lube with white lithium grease. Are the calipers new or rebuilt? If rebuilt, I've seen the reman guys just blow them out and reassemble with new seal without honing the cylinders out. When the new seal scrapes across the ridge it starts leaking and could bind.

there are no "cylinders" to hone out on disc brakes and the OP put in pads and calipers so there no chance of rusty pins and rusty pins don't cause the brakes to work properly for a while and then slowly tighten up and get hot
Based on assuming all the work done was done correctly and all pertinent ajustments made correctly I would say that maybe the
proportioning valve is faulty but that's a rare condition
it does sound like the MC push rod is not set correctly
Is it the front brakes or the rear sticking on? have you checked that out?

[turbojimmy]

I have a similar problem with my '84, but it appears to be limited to the right front caliper which causes the stiffening of the pedal. It came on out of the blue and I haven't been able to figure it out. New calipers, rotors, pads, MC and soft hoses. If it were all brakes I'd suspect something in the Hydroboost system but it's just the right front. I just live with it. It never locks up completely and frees up after a little bit of non-braking travel.

Sorry I don't have an answer but subscribing for replies....