sticky brakes

[molly]

I have a 84 Carrera that I have had for a long time,it has been relatively trouble free.I have removed the ac,backdated the heater,test pipe.It has been a commuter car for years.My current problem is the rear brakes seem to be dragging.Ihave checked the rear pads,moved the pucks back in and wheels spin free.after applying the brakes a couple pumps the wheels are dragging again.parking brake is free.Is it sticking calipers,malfunctioning residual pressure valve

[DRACO A5OG]

It could be your Proportioning Valve in the frunk. but before that let's make sure your lines are not clogged.

This require you to disconnect the brake line at the caliper and check the flow. If you have the original rubber lines they could have corroded and swollen, causing a restriction as a result improper retraction of the pistons.

If flow is good then it may be time to service the calipers and make certain you use some sil-glide on the pistons after a thorough cleaning.

If that still does not do it then the proportioning valve could be the culprit.

Jim

[molly]

I did bleed the rear brakes.I am starting to think there is built up grime and or rust on the pistons and or bores leading to incompleat relese.Nobody wants that!This time I not going to throw money at it till I replace the problem part.

[CCM911]

Time for a caliper rebuild, Molly. DOn't be bummed, the parts cost will be under thirty dollars, and it is really easy to do the rebuild. You can bang this out on a Saturday.

[Trackrash]

If your car still has the original brake hoses, I would change them no matter what. They can seem fine, fluid will squirt out, but still they will cause this problem.

Before you rebuild, you could bleed the fluid again. But when you do the bleeding, push the pistons back into the calipers when you have the bleeder valve open. Close the bleeder and pump up the brake pedal. Repeat.

Many times this will work to free up sticking pistons. While in there check to make sure the pads are free to move. Sometimes crud will make them stick.

[BK911]

Usually I would agree to find the defective part then fix. But in this case, 4 new rubber brake lines and 4 caliper rebuild kits. Its time!!

[heimtun]

+1 replace brake lines if original. I had the same type of issue on a 1984 BMW.

[speeds5]

I had this happen to the front right corner. Caliper piston was not going back. Rebuild it and you'll be fine.

[Quicksilver]

So your total list is:
- Bad caliper
- Bad portioning valve
- Bad rubber flex lines

I REALLY like testing things before replacing but the only way to test is to get a pressure gauge that will deal with brake pressures. Not an easy, cheap test...

[911 Rod]

Rebuilding calipers and upgrading to SS lines is considered normal maintenance on these cars.

[Quicksilver]

It occurs to me that the sticking brakes will generate heat. If you have an IR thermometer you can use that to see if it is creating more heat on one side.

It is really unlikely that you would get the same failure on both sides and even if you did you wouldn't get the same level of failure.

Does one side heat up when it is sticking? If so that side has a caliper or flex line issue. If both sides heat up it is going to be an issue back up where the rear circuit is a single line which leaves you with only the portioning valve and the MC. (And I can't see the MC retaining rear pressure without also retaining front pressure.)