front brakes jam on

[karlio]

my c30 rv had to have a leaking master cylinder changed a couple of months ago.i entrusted this to a local garage who have done lots of work for me in the past,but not on an american.
everything was ok but they a had a job bleeding the system.given the ok i picked it up and drove home.8 miles into the journey she got slower with my foot getting further down on the throttle.crawled to a stop.front brakes very hot and smelling.truck now refused to move brakes jammed on.recovery truck tows me away.i send the rv back to the garage.they say front flexi pipes may have collasped.i got some new ones for them.they then still have a heck of a job bleeding the system.finaly get the ok.drive home some 20 miles and all fine.load up the rv to go racing at silverstone on friday.travel 1.5 miles and the same thing happens.front brakes jam on and cannot move.
i realy lost the plot this time and had a word with the garage,still not calmed down now.

i read on here that the master cylinder has to be bled first then the pipework.is the above a sympton of that or are we missing something else.
after an hour or so the brakes have cooled the rv will move again
the foot pedal has always been hard to push down and now there is very little downward movement.

cheers
karl

[blazing816]

Sounds more like your calipers are seized to me. Sounds like piston in the caliper is not "retracting" when the brake pedal is released, so the pad are rubbing 100% of the time. That would be the reason your pedal doesn't go far because the pads are already up against the disc. The calipers for our trucks are no more then $30 at local auto parts store, I just replaced mine front ones, because one of my calipers was sort of sticking (nothing that bad) but it was heating up the disc and "chewing" it up. SO I replace both calipers and the disc/hub assembly. Just my $.02

[frotosride]

two things...firtst the proportioning valve may need to be adjusted/cleaned or possibly replaced. Secondly it could also be the master cylinder. If the clearances are not right it can easily cause the problem especially with the lack of travel in the pedal with new master cylinder. I would first shcek the valve. I may have missed it but do you have standard vaccum booster or hydraboost?

[karlio]

thanks for the replies chaps.all helpful.
my son-in-law erny(mechanic) came over this evening to have a gander.we have found that the piston on the hydraboost is just pushing the mastercylinder.should there be a metal shim between the hyra and master cylinder mating faces.

we jacked the front up and had great difficulty turning the wheels until we started to release the master cylinder fixing bolts.this let the wheels turn a lot easier.a washer as a spacer/shim seems to have made a lot of difference when all bolted back up.
we also whipped the wheels of and popped out the pads as these are well beyond anymore use.lubed up the caliper pistons and got them moving a bit more freely.put all back and a lot of difference.

just for our piece of mind we then took out the shim washers and could definatly feel the calipers starting to bind again.

if there is no shim steel between the master and hydro do i have a badly made master.

if the propotioning valve has gone would that normaly effect the rears rather than the fronts.

thanks very much

karl

[karlio]

forgot to ask,what kind of fluid goes in the black cylinder reservoir on the hyrdraboost.

cheers
karl

[frotosride]

not sure exactly which reservoir you are referring to but if it is on top of the master cylinder than DOT3 brake fluid...

[Jason S]

The hydraulic portion of the hydroboost system is part of the power steering system. The power steering reservoir is usually at the front of the engine above the power steering pump or integral with the power steering pump itself. It should use regular power steering fluid.

[Irish_Alley]

The hydraulic portion of the hydroboost system is part of the power steering system. The power steering reservoir is usually at the front of the engine above the power steering pump or integral with the power steering pump itself. It should use regular power steering fluid.

[diphthong]

 Does this RV have a hydro-vac or vacuum assist system?


I once had a shop owner tell me "it's possible to have just one plug wire crossed"   :-)

[diphthong]

To troubleshoot this I would start by cracking the bleeder valves on the front wheel cylinders than the rear one.  Just barely open them just enough to determine if there's pressure buildup.

If you open the lines too much you will lose all the pressure and this test will not be reliable. Also crack the lines at the master cylinder.

You're trying to determine if it is a residual pressure problem, and how far down the system the high-pressure is present.

It's been 10 years since I've seen one of these systems but what I can recall is, Hard pedals usually go back to a problem in the power to assist system, Which should increase the pressure to all four wheel cylinders, Not just the front.

Anyway, First, you need to determine if it is a pressure problem Just to the front wheels Cylinders.


Good luck,








I once had a shop owner tell me "it's possible to have just one plug wire crossed"   :-)

[diphthong]

It's interesting all this happened after the master cylinder was changed...

I read your post a little closer, this may be what happened here: You mentioned they had a hard time bleeding your system.  If they messed with the depth of rod that connects your brake pedal to your master cylinder / Hydro-vac system.  An incorrect adjustment of this rod could explain all the problems are experiencing.

Look under that at dash at the locking nut that secures that rod and see if there's fresh scratches on it, you're looking to determine if someone actually change the death of that rod. 


I once had a shop owner tell me "it's possible to have just one plug wire crossed"   :-)