Rear Brakes Seizing

[Frog]

Okay, so the car has sat for 5 years. I finally get it all in running order, and then the rear brakes seize. I drive home about 3 miles with rear brakes applied.

I replace all 4 calipers, all pads, and all 4 rotors.

Went for a test drive and drives fine for about 1/2 mile and then the rear locks up. I am still having the same problem!

Left the car out for a few hours and the rear brakes are still locked up

Car has ABS.

I am sure both rears are locked up.

[Liquidity]

If you're 100% positive both rear brakes froze up, it's most likely your proportioning valve. If only one froze up, it's a bad soft line.

[LJ851]

Okay, so the car has sat for 5 years. I finally get it all in running order, and then the rear brakes seize. I drive home about 3 miles with rear brakes applied.

I replace all 4 calipers, all 4 disks, and all 4 rotors.

Went for a test drive and drives fine for about 1/2 mile and then the rear locks up. I am still having the same problem!

Left the car out for a few hours and the rear brakes are still locked up

You replaced 4 disks and 4 rotors?

[Frog]

If you're 100% positive both rear brakes froze up, it's most likely your proportioning valve. If only one froze up, it's a bad soft line.

Yes, both are locked up.

I read that it could be Brake master cylinder/brake booster/ABS unit/Pinched brake line. Would any of these make sense? Could the master cylinder cause a problem with the rear only? Or are all 4 corners the same as far as the MC?

Where is the proportioning valve? Is it this: 34-33-1-152-494

A little more info:
Car has ABS

You replaced 4 disks and 4 rotors?

Ha! I meant pads. Thanks, fixed.

[Frog]

Also could it be as simple as not compressing the caliper pistons enough upon install? I have never had this problem before and I have done full E30 Brake overhauls on 4 cars now.

Are you supposed to fully compress the piston upon install before bleeding?

[jlevie]

My first suspicion would be the brake bias valve, followed by a bad ABS unit, followed by a bad master cylinder. With the brakes locked up, crack the to line from the bias valve to the ABS unit. If that doesn't release the brakes the bias valve is bad. If that works, get the brakes locked up and crack the line from the ABS unit to the master cylinder. If that makes no difference the ABS unit is cause. If that unlocks the brakes the master cylinder is bad.

[Frog]

My first suspicion would be the brake bias valve, followed by a bad ABS unit, followed by a bad master cylinder. With the brakes locked up, crack the to line from the bias valve to the ABS unit. If that doesn't release the brakes the bias valve is bad. If that works, get the brakes locked up and crack the line from the ABS unit to the master cylinder. If that makes no difference the ABS unit is cause. If that unlocks the brakes the master cylinder is bad.

In my mind it is flipped. If the line from bias valve to ABS doesnt release the brakes, wouldn't be the ABS unit?

isn't it:
MC ----> Brake Bias Valve ------> ABS --------> Caliper

[jlevie]

No. The bias valve is between the ABS unit and rear brake circuit. I.E;,

MC->ABS->Bias valve->calipers

[Frog]

No. The bias valve is between the ABS unit and rear brake circuit. I.E;,

MC->ABS->Bias valve->calipers

Oh, thats why it was backwards in my head.. Okay, that makes sense. So the valve could be bad by not releasing pressure from the rear calipers. I think either way i skin it, whether it is the Bias valve, the ABS, or the MC, it's gunna cost me $100.

I don't think its the MC, because it would cause a problem to all 4 calipers, not just the rears.. right?

[jlevie]

Oh, thats why it was backwards in my head.. Okay, that makes sense. So the valve could be bad by not releasing pressure from the rear calipers. I think either way i skin it, whether it is the Bias valve, the ABS, or the MC, it's gunna cost me $100.

I don't think its the MC, because it would cause a problem to all 4 calipers, not just the rears.. right?

The master cylinder has two sections. One for the front brakes and one for the rears. I doubt the master is the cause.

[Frog]

Bought all 4 re-manufactured calipers at NAPA (eclipse brand) so I assumed they were good, but this issue ended up being the rear caliper seizing. I guess one was sticky and the other was completely seized. Replaced the one that was seized and re-bled and all is good.

This all just really threw me off.. I replaced the brakes because the rear was seizing, then the new calipers, 1.5/4 were defective and happened to be the rear which was the reason why I was replacing them in the first place.. This led me to believe it was something other causing the rear to seize, because what are the odds that they were bad?

There you go guys, check re-man parts because they're not always good. Thanks for the help.