Rear brakes locking up

[Pheret]

A few months ago I noticed my rear brakes sticking from time to time. I drive 60 miles round trip a day on the highway. The brakes would grab, causing the car to vibrate pretty badly then after a couple miles they would release and back to normal. Eventually the Passenger rear pads went from good to zero in about a day when I tried to brake on the highway and hit the floor. The Passenger caliper piston had literally fused into the pad backing plate and basically exploded. I picked up a pair of used, seemingly good calipers from a local parts car. I replaced the caliper and pads on the passenger rear and the pads on the driver rear. This was a few weeks ago.

Not all was well, brakes still stuck until the driver rear caliper exploded too. That was last night. I replaced the driver caliper and both pads again, all seemed well last night on the test drive. During my commute this morning the brakes locked up yet again, basically drug the car to school. Upon arriving at school I had two flat tires on the driver side (not related) and the pads on the passenger rear were digging back into the rotor.


I don't know where to look next. I never use the e-brake and it seems to be functioning properly although I don't see how it would be related any way. I need to replace the rear brakes again, and the fronts are getting close so I figured I'd get them done too. Aside from the calipers is there something in the rear that would cause the calipers to lock then release a few miles later?

Need to get this problem fixed asap since my other car, a jeep, isn't highway safe due to the new development of the dreaded death wobble.

[jlevie]

The first question I'd have is whether you are seeing excessive wear on both sides? A lock up and excessive wear on one side, but not the other will be a problem with the caliper or the soft lines on that side. But if both sides are affected the problem will likely be from the tee above the subframe forward. That could a bad bias valve, problem in the ABS unit, or a bad master cylinder.

If faced with this I'd:

Replace all the soft lines in the rear
Rebuild the rear calipers
Replace the bias valve with a new (not used) part

That eliminates any chance of the rear of the car being the cause and those are just good maintenance items. Then I'd drive the car and see if there were still problems. The easy way to tell, without causing other damage, is to drive the car a few miles and check rotor temperatures with an IR thermometer. The front rotor temperatures should be a bit higher than the rears. If the rears are significantly hotter than front, the calipers aren't releasing.

If the problem is still present I'd replace the master cylinder as I've seen it cause this more often than the ABS unit.

[Pheret]

Thanks for the quick response!

As for wear, it's affecting both sides, I guess the passenger rear just happened a little faster than the driver rear. As for the bias valve, would that be the pressure regulator I'm seeing Here?

I'm in the process of ordering new pads, rotors, inner and outer hoses, wear sensors and caliper rebuilding kits now.

[jlevie]

That is the two varieties of bias valves.

[Pheret]

How would I know which I need? According to realoem it's the former.