Help troubleshoot front disc brakes sticking

[pokey64]

Just starting to put some miles on our Camaro and are working through the Gremlins. Our latest is that both front disc brakes start to grab/stick after a couple miles of driving. We start to smell burning brake pads and they get scorching hot. If you jack up the front end you have to push pretty hard to spin the wheel. After the car sits for a while the wheels will spin freely again. The brakes feel firm and there is not any play in the peddle.

The setup came with the car and I belive it was from CPP. Everything seams to be pretty new looking.

Heres a list of what I've heard for suggestions so far:
Sticking proportioning valve (I have heard they rarely ever fail, looks pretty new)
Contaminents in the fluid (had a leaking rear line so was just changed by the local shop)
Wrong brake fluid/brake fluid boiling (not sure what they used but had issue before)
Sticking pistons in the calipers (calipers look pretty new)
Inside of hose breaking down and acting as a check valve or collapsing (hoses look pretty new)
Pre-load on the master (I removed the master and checked this one. It looks fine)

The local shop seemed to be grasping at straws and I am not really sure of the right way to troubleshoot the real issue. Where would you guys start?

Here are some pics of the setup.

Thanks! :thumbsup:

[GregWeld]

Wrong hook up at the master cylinder? Not all MC's have front reservoir going to the front brakes - I would check with the supplier/manufacturer. I'm wondering if it doesn't have a built in residual valve keeping a couple pounds of pressure on the pads. If it is a MC built with this feature - and the line was meant for rears with DRUMS... i.e., a combo valve or a residual valve built in.

There was no reason to "look" at the MC if you have pressure on it from a improperly set up brake pedal/rod.... you should have 1/2" minimum dead pedal -- where it moves that much before ever pressuring on the MC.

The calipers appear to be floating....

With no pressure on the MC -- you should be able to "move" the pads a bit... are they loose with no pressure? You should be able to at least rattle them.

Since the car works FINE COLD -- it would seem to me that you have residual pressure on the calipers causing just a bit of drag - then with the continued heat of that drag - the brakes get hot and you've got your trouble. Try spinning the tire cold - then have someone apply the brakes - and spin it again to see if there is now residual pressure/drag.

If someone put the lines to the calipers using teflon tape - a no no - make sure you remove that tape. The problem comes from a little of the tape clogging the line. It might move with pressure from the master cylinder - and then act like a check valve as the pads try to retract...

Is there a combo valve in line? If so -- make sure it's plumbed correctly.

[GregWeld]

There is a simple though not foolproof method of checking to see if your system has residual pressure. With the brake system at rest, open a bleed screw on a wheel cylinder or caliper. If even a few drops of fluid come out, residual pressure is probably present. If the wheels are off the ground on a disc brake car, depress the brake pedal firmly and lift off. Attempt to turn the wheel just slightly to feel the amount of drag. Open the caliper bleed screw and close. If the wheel now turns more freely, residual pressure is probably present.

Occasionally, another problem in the brake system will be mistaken for a residual valve. This is when the master cylinder pushrod length has been improperly adjusted in such a way, as to not allow the piston to return all the way to the back of the bore. If the piston does not return all the way, the cup in front of the piston will not move back far enough to open the bleed hole. When the bleed hole is not open, residual line pressure is the result. Unfortunately, this type of residual pressure is not controllable and gets worse the harder the brakes are applied. Master cylinder pushrods always should have "free play" to insure that the piston can return all the way back when pressure is released.

[pokey64]

Appreciate the info Greg! :cheers:

Went out for dinner with my family last night so I didn't have time to play with the brakes. The car was scheduled at the shop today for some other items so I ran all this past them. In the end it was the master cylinder pushrod length. Took it for about a 20 mile spin jacked her up and the wheels spun freely. I thought I had checked this out last weekend but I guess I don't know my head from my mASSter cylinder. :D

One gremlin down but looks like I found another on the drive tonight. I'll know more this weekend.

Thanks again!