Rear Brake binding.

[sleepdoc]

Hi All

73 914

After a rebuild and new pads I have a problem with my rear brakes. The disks are new, and for this problem the emerg brake detached.

I set the "venting distance" to a generous .008. At this point the wheels spin free.

After driving about a bit the rears start to drag, and then smoke, you know. I tried to back the calipers off a bit more when they were hot but the pistons are as far in the cylinders as they can go. The problem is not that the pistons aren"t retracting correctly.

It seems that the disk/pads are expanding enough to interfere more and more as they get hot. Could it be that the metal impregnated pads start out a bit to thick so that there isn't enough room for expansion?

Anyone have any other ideas.

Thanks Mark

[Ron Meier]

Did you have any problems sliding the pads in? I ground the vertical edges of my new pads with a bench grinder so they would move freely as they were a bit tight. Seems the mfg was trying to give a deal by leaving a little excess material, but I saw it as sloppy QC.

[Dave at Pelican Parts]

That is very strange...

How can you tell that the brakes are actually retracting? That would be my first suspect.

I run 0.004" of rear venting clearance on my car with no problems.

--DD

[Joe Ricard]

I would pull the pads and look at where the pad is supposed to slide. Mine had lots of crud that resembled RUST. I pulled the calipers off cleaned up the frame and pads slid like snot on a door knob. I also put in new caliper piston seals (while I was in there) and everything works great. I also needed to do what Ron did and trim touch off the pad metal backing. Sort of like match fitting.

[clr2cont]

check your rubber brake lines...after time they may be acting like check valves and not allowing the pressure to return to the master cylinder and are holding the brakes slightly applied..when they stick open a bleed nipple and see if they release...if they do something is keeping the pressure applied and it is most likely your rubber lines...


clr2cont
www.clr2cont.com

[sleepdoc]

Thanks for the sugestions.

I cleaned the caliper frames, ground down the edges of the pad backs, and the lines are new stainless.

How about this idea.
The problem is heat related. The symptom is exactly as cle2cont suggests, that is the pads start to be applied when they get hot and stay applied. All the pads are affected when this happens. If I open a bleed a bit of fluid spurts out and they are all released. If I stop and let the system cool the pads also release. As long as I use the brakes gently this doesn't happen. It happens when I try to bed the new pads. I haven't yet been able to bleed to a firm pedal. Maybe the remaining gas in the system expands at temp causing the pistons to be applied?

thanks Mark

[clr2cont]

that idea sounds like it cause the problem ...however, the onlytime the lines to the calipers remain pressurrized is when the master cylinder is derpressed when it is released any pressure is returned to the brake resiviour. so knowing this if the remaining air was heating up and expanding to pressurize the system the master cylinder so let the pressure by into the resiviour. Two things I would ensure..1 is the brake pedal allowing the master cylinder to return to the full resting position? if not then thats what could be holding the pressure on. 2. you have to get that air outta there before you really can trouble shoot the problem...

Im having a bad time with brakes to and It is all pointing to my master cylinder...

wait one more idea...when you said you open the bleed nipple pressure is released.... when the pressure builds up open the brake line for the rear brakes at the masster cyclinder...if it spits fluid under pressure then their is no bloackage betweeen the caliper and the master cylinder...if not then you could have a blocakage at your proportioning valve or in the steel lines, that is acting like a check valve...

I know the feeling hope this helps..

clr2cont

www.clr2cont.com