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I'm currently 700 miles into a cross country trip and i am somewhat stuck. my 1993 p-30 chassis 454 motorhome has had all 4 new rotors, pads and calipers replaced. after driving approximately 10 minutes i can feel the brakes start to drag and then they eventually lock up. it might be important to note that i am on a highway and do not touch the brake pedal.
after sitting for quite some time and cooling the brakes will release and i can drive another mile or two.
i was towed today to a shop and the auto-brake cable was disconnected to the drum behind the transmission. i still have the foot operated emergency brake connected and that works fine.
after going for a test drive just now i have noticed the brakes starting to drag again. the mechanic from today suggests replacing the booster mechanism. apparently there are two parts to this and a rebuilt unit costs about $300. installing it will be another $300.
it seems like it is just building too much pressure (which i can feel in the pedal a bit) and was wondering if this is the best course of action or is there something else i can try first.
i am just sitting here in a truck stop parking lot until the shop opens monday morning.
i was able to crawl under and make sure all the rubber hoses were replaced to the calipers. i also have one of those fancy infared tempature readers. after locking up the front brakes were both close to 500 degrees and the back were a little under 300. i am guessing that its normal for the back to be cooler. side to side the temps were almost exact.
i just bought this rv a few weeks ago after it was sitting for several years. one of the brake pads was missing and the caliper was grinding against the rotor in the front. same thing with one of the back brakes. rather than replace just one rotor on each axle i decided to replace all four.
the thing stops and goes flawlessly now until you hit about 5 miles and then the pressure is building somewhere and locking the brakes. this almost always happens without me ever touching the brake pedal.
after being parked for a while i can put it in nuetral and release the parking brake and there is no brake drag. you can push the rv back and forth jsut by leaning on it.
its starting to sound to me like the mechanic is right (unfortunately for my wallet!!) and something external is building pressure. i dont know anything about this power-steering pump assist but i am guessing there should be a return valve for excess pressure or a switch that shuts it off if pressure builds too much.
is there any way to test this before replacing it to make sure its the right thing being done?
its a shame i cant get up under the wheel well far enough to see how the master cylinder is working. they really put this in a bad spot!!
Sounds like front are getting hot.If you stay under five mph, I guess nothing gets hot.If one hose or one caliper was bad I think one side would be hotter than the other.Does the parking brake only work on the drive shaft.???Don't know anything about newer systems.If it only works on the drive shaft you may have something there with the pump.Hey you can take the belt off the pump and test it without the pump----- REMEMBER NO POWER STEERING OR POWER BRAKES WHEN BELT IS REMOVED----.I think it is the back belt-the short one on my Itasca.Maybe the mechanic can do that test.I see lots of post on RV.Net where the new type parking brakes hang up locking the coach brakes up.You must have been reading the rotor temp.I am going to get my manual out on the boost pump and see what it say about lock up...MIKE I guess the foot parking brake works on the drive shaft.If I find something I will repost.
One more thing common on the P30s is a brake hose starts coming apart inside and plugs up wheel cyl.or the master.Will do the same thing brakes lock up. Do the wheel temp test if you can and see if one is hot. MIKE
Hi Eddie Mike here,sounds like you have some big troubles.I just finished my 86 Itasca front breaks a few days ago.When brakes start to drag I would go out and feel all four hubs not hub caps.See if one is much hoter than the others.I had my front left locking up,but when left starts building up pressure it all so builds pressure on the other side.New systems may even criss cross.I see you have 4wheel disc. If all are same temp my have other problem.Was the master cylinder removed during brake work.??Why were all rotors replaced.???Was it locking before brake work.???Were the caliper slides lubed during install.Did the mechanic teel the hubs during test drive.Was the master cyl.flushed out with clean brake fluid.May have dirty fluid and plugging up the return hole in the master cyl.With cover off top of master cyl. have someone apply brakes,engine off.look for a spurt of fluid in master cyl. It just squirts up a bit in top of fluid.If no squirt the return hole is pluged or the push rod on the back side is adjusted to far forward.Thats why I asked if master cyl. had been removed.Don't know where your master is but hard to get to on my Itasca. Well just a few ideas Eddie, Hope this helps.I will check this post in the AM for any other info you may have. Good Luck Mike
Hi there,
I drove my P30 RV for almost 8 days without problem. One morning I drove it for about 10 miles and my front brake lock without touching the pedal. After approx. 40 minutes everything was fine for the rest of the trip. 2 weeks later I was driving downtown and the same problem again. After 40 minutes the brake release and I was go to go.The fluid are OK in the P.S. and the Master Cyl. Do you have any idea?
One more thing that can cause lock up,Check the brake pedal return.Pedal should have about one inch or a bit less free play.Sometimrs the brake light switch that rides on the arm of the pedal will get kicked or bent and not let the pedal return all the way back up.Or anything under the arm that does not let it return all the way up,This keeps the return hole covered inside master and fluid can't get back inside cyl.The new p30s have a different system for parking prake,and I have not worked on them. Check the post on RV.net OPEN ROAD FORUM. Lots of post there on parking brake hanging up. If its hanging someone can tell to free it up. Good Luck Mike
Well Eddie it looks like parking brake is on the drive shaft only.The manual does say brake drag can be proportioning valve faulty,faulty meetering valve,plus the things we talked about above.Not much on the hydro boost mostly talks about seal leaks on it.To bad its so hard to get to the master cylinder,it can tell so much.I just have a gut feeling problem is a drag on one of the wheels and heats up brake fluid causing pressure build up.You didn't say if hoses looked new or old.There is a kinda field test for the booster.Engine off pump pedal 5 or 6 times to deplete accumulator.Depress the brake pedal,approx.40 lbs pedal force,start engine.The pedal should fall and then push back against the drivers foot. Keep us posted if we can help..MIKE
32' 94 Bounder w/454 Chevy - Automatic parking brake won't disengage after backing up. Locks in and won't allow me to go forward. Had the cable disconnected, but have to use hand brake whenever I stop and park. Unable to find anyone who knows anything about it.
I have a 2000 Allegro with a p-30 chassis and the auto park kocked up 3 times the last time it had to be towed out of the mountians, has ther been a recall for this??
First check if you have abs on your rv by turning your engine on. a light of abs should come on. if you do have it check the connection make sure is not crack broken on dangeling. your booster has an adjustment that might help your problem. also check your brake lines for bend or kincs. or it looks out of the ordenary. I hope this will help you
Eddie,you must have had all this work done before you left on this trip.The brakes worked for 700 miles.Just makes me think your problem maybe dirty fluid blocking return of brake fluid,or a bad hose.With new calipers piston should not be sticking nor caliper hang up even if they were not greased. MIKE
I have the same problem with brakes locking up. It does not happen during lower ambient temperatures, When I go to the mountains or the ambient temp is 100 degrees F the brakes lock up.
Has any one contacted GM over this? it is a major safet matter.
Thx,
Jon
Eddie, Did this fix the problem ?because I am having exactly the same issue. It took me 7 hours to go 22 miles and overheated my new 454 twice in the process.
email eddie
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