i am running disk/drum setup and the back has started locking up on me. the first time it happened was on the highway at 60 mph and now they lock up with hardly any pressure. i replaced the wheel cylinders and bled the system just in case but they still lock up. am i correct in thinking it is the proportioning valve? if so can it be cleaned and reused or do i need to suck it up and get another one?
Sounds like you're sending to much fluid to the rear. This would be the proportioning valve. If its adjustable, you can just decrease the flow to the to the rear. You can buy valves already set up for your app., or you can buy adjustable ones.
Make sure the shoes are retracting! Check my post. http://www.jalopyjournal.com/forum/showthread.php?t=158333
Is this a new brake system or something that has thousands of proven miles? If it is new, what was changed.
My pop's shop truck which I almost burnt down cause the brake stuck, had the same problem on the front... went through and complete rebuilt the brake with brand new parts, rotors and all... Still locked up on him... Figured out it was a bad brake line, must have had a small flap of rubber inside that when pressed would energize the break and at let off the flap would catch and keep the brake engaged.
Make sure you have about 1/8 play between the the rod and the master before it plunges or it will not let the fluid retract. In other words do not let the pedal rest against the plunger in the master.
how old is the rubber brake hose? They swell over time and act like a check valve holding pressure on the shoes,building up heat and eventually locking up the brakes. Also I have had a similar problem on a bike. The hard line had gotten pinched a little...it was enough that after riding 10 or 15 miles the rear caliper would lock.
ive taken a look at all the stuff u guys suggested and its still goin on, so i guess its off to the junk yard, any particular prop. valve i should be looking for? its on a 50 chevy truck with disks up front and drums in the rear
BE CAREFUL with your brakes. Don't take chances with junkyard parts. I had a similar problem on a disk/disk setup. Brakes would lock up after about 10 mins or so and stay locked for a while. As chaddilac and brewsir mentioned the bad rubber hose is a likely suspect. I replaced proportion valve - same problem. I pulled 15in of vacuum on line going to rear brakes and opened connections until I found the problem - bad rubber hose. These guys know brakes - www.mpbrakes.com or these www.inlinetube.com/pro_valves.htm Good luck, please let us know what you found.
i had that problem once kept bleeding the brakes and replacing the wheel cylinders come to find out i had a broken caliper bolt that would put the caliper at an angle with any brake pressure might be the problem eventhough its not a common problem
can a rubber hose still be the problem if there is only hard line running to the drums? it would be easier if this was the case, but i dont want to go messin with the front brakes if i dont have to
actually junkyard parts that come off wrecked cars were working the day the car was wrecked. beware of backyard abandon cars. they were parked because something was broken. i would suspect the m/c my self.
make sure your rear brake lines aren't near any heat sources,this causes the fuild to boil and apply pressure
Of course a bad brake hose can be at fault on a rearend. You do have a hose there don't you? All cars have at least three brake hoses, one to each front caliper or wheel cylinder and one to the junction block on the rearend, or four, same in front but 2 in back, one going to each wheel cylinder. There are a few NEVERS when building a brake system: 1. Never use "used" brake hoses. 2. Never use rebuilt master cylinders. 3. Never reuse old brake pipe(steel lines). 4. Never think it's good enough when something is wrong and you know it. 5. Never forget to test that system before hitting the streets. If you don't care about yourself and your passenger/s, at least give a little thought to the rest of the world out there. 6.
well i think i fixed the problem, i replaced the m/c and all the hoses and that seems to have done it. u guys once again proved why this place kicks ass, i appreciate all the help.
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