rayrat

On a 99 Z28, What causes the front caliper pistons to retract after applying the brakes? Mine seems to be too stiff and the wheels a little hard to turn after getting off the brakes.

I have a 85 Trans Am too and the I can spin the front wheels (when it is jacked up in the front) like it has no front brakes at all---no resistance.

Is this a characteristic of the 4th gen Camaro?

babbage1109

iTrader: (11)

The pins that float the calipers could be rusted to the bracket

trans_am7935

iTrader: (15)

to answer your question, heat pushes the pistons back in created by friction.

i would also check the caliper pins, they seam to be the possible culprit here.

speed_demon24

iTrader: (6)

Uh what? The disc pushes on the brake pads which pushes them back in...

z28bryan

iTrader: (7)

lol. This thread is funny

I want a try...

What causes the pistons to be pulled back in? I'm going with the brake fluid causes the pistons to suck back in when the brake pedal is released. Releasing the brake pedal sucks the fluid back into the system. The fluid sucks the pistons back in.

How did I do?

1981TA

iTrader: (7)

several things can cause a caliper pad to push back. The rotor is probably the biggest cause, via uneven surface/warping, axle movement or bearing play-- basically anything that makes the rotor surface move in a direction *other* than the rotation involved with regular driving. I'm not a brake expert by any stretch, but I believe disc brakes are designed so that the pads ride on the rotor slightly. Without pressure on the brake pedal (or some sort of malfunction; like seized caliper slide pins), there isn't enough friction caused by this to produce noticeable stopping or heat.

Drum brakes, on the other hand, have springs built into them that actually pull the brake shoes back away from the drum braking surface. When the pedal is not being pushed, there should be no contact between the shoe and the drum.

rayrat

I have replaced the guide pins. I have even removed the pads, reinstalled the calipers to see how easily the calipers move back and forth. And the calipers move easily. I have replaced the calipers, the caliper brackets, the pads, the disc and the brake hoses and still the same.
I have a Ford 9 inch (Moser) and the ABS sensor is no longer in the rearend. The ABS is still in the car and the only thing that it is detecting is the front brakes since these are the only sensors hooked up. Could the ABS computer on the LH fender well be causing this.

Thanks for the replys.

wssix99

iTrader: (5)

See this for some more info:
https://ls1tech.com/forums/suspensio...orsepower.html

timseitz

Unplug it and then see what you get.

rayrat

Thanks for the link wssix99. I have unplugged the ABS and the brakes still drag. All I get is a trouble light. I understand about the brakes dragging but this is a little too much. The RH brake drags more than the LH brake. Do the ABS delete kits come with electronics to delete the trouble cods and service lights? I have to pass emission and computer testing to get an inspection sticker every year.

wssix99

iTrader: (5)

If you've replaced the pins and can slide them with your fingers, I'd next check for seized caliper pistons. You should be able to press those in with your fingers, also. (Not easy or fast, but they should move.)

Does the car pull to one side if you go down a flat road and take your hands off the wheel?

timseitz

if you have unplugged the electrical components your problem is a mechanical one.

rayrat

Thanks for the replies, really appreciate it. And yes it pulls to the right because that is the front wheel that is the hardest to turn.
I was told that there is a proportioning valve inside the master cylinder for only the front wheels. Has anyone heard of this?
Don't want to start charging parts again but if that is what I have to do then......

1 FMF

iTrader: (1)

this would not happen. there is a fill hole in the master cylinder where the reservoir connects and allows fluid into the master cylinder, which then gets compressed when brake pedal depressed and fluid gets pushed out the side holes in the master where the lines go to the abs module then split to 4 wheels. when you release the brake pedal and the plunger inside the master retracts back past the fill hole, it's an open system and there is zero pressure. at best there is a few psi at the calipers due to gravity of the master cylinder being higher than the calipers, so the calipers would always see a slight bit of pressure. there are no return springs in disc brake calipers, the pads always ride up against the rotor and they need to otherwise you would have brake pedal travel and/or would have to pump the brake pedal to gain enough pressure at the calipers to stop. your brake pedal travels something like 6 inches total, actually what matters is master cylinder piston travel and the diameter of that piston which is usually around an inch. compare that to the caliper piston total diameter and that's how you calculate your braking force and how far the caliper pistons can move- no different than a hydraulic bottle jack.

for a 99 z that has the oem brakes which are 4 wheel disc with the abs modulator, there is nothing else to the system. what you need to do is remove the bleeder screw and put a pressure gauge from a brake kit on the caliper. pump the brake pedal and create pressure then release the pedal and see what pressure falls to, and you can compare it to the other front. my guess is if the caliper is good then your abs modulator is causing a problem and i believe this is how you diagnose it. and actually you may not even need a pressure gauge, when you think the caliper is hanging up just open the bleeder and see if brake fluid squirts out, if a large amount does then you know it's holding pressure. with the bleeder open if it instantly stops hanging up then you know. only other thing i can think of is the caliper is bad and the pistons (not the slide pins) are sticking which is pinning the brake pad against the rotor. this is common so i would check this first, you seemed to say the caliper was fine and mentioned slide pins are free but i didn't see you say specifically you removed the pistons from the caliper and checked the bores and piston faces. don't assume just because you can push the caliper piston back in by hand that it can't wedge under operating conditions. with the caliper hung up and dragging open the bleeder screw if it still drags then it's bad pistons in the caliper, for the low price of new calipers just get 2 new fronts, don't bother trying to rebuild them unless you really need them for some reason.

wssix99

iTrader: (5)

When you say "turn," you mean turn with your hands with that wheel raised off the ground, right? (ie: not turning the steering wheel)

If so, and if your pins are good, and if the car only pulls to the side with the brakes sticking, it sounds like a classic bad caliper.

z28bryan

iTrader: (7)

Oh ok, so the pistons don't actually go back into the calipers much? They just sit where they are and apply pressure when the brake pedal is depressed?

wssix99

iTrader: (5)

As the rotor spins, air pressure builds up between the pad and rotor, pressing it away by just a fraction of a fraction of an inch. When this happens the piston is pressed back in a very small amount.

If the piston is galled or out of sorts, the normal pressures on the brakes won't be enough to press it in by that small amount and the brakes drag.

More commonly, stuck pins will cause the problem but the pistons can also get galled or build up contamination through corrosion or dust getting in behind the boot.

rayrat

Thanks for the info and the replies. Especially thanks to 1 FMF for the detailed information. And sorry about getting back to you so late.

I would still like to know about the ABS delete kits availeable out there. Will I be able to delete the trouble codes and such. Anyone out there experienced with the ABS delete?

roy

May want to check your sources on that statement.

wssix99

iTrader: (5)

If its the wrong answer, why don't you enlighten us with the correct knowledge?