Sticking Brake Calipers

[Jaymanbikes]

I changed my 77 280z front disc calipers to the Toyota PU Calipers and the ZX master cylinder. Everything fit perfectly, clearance between the pads and the rotors was perfect. I then bled the system and both fronts are sticking. If it were one side I would say bad caliper but both are doing the same thing. Any thoughts one what might be happening? 

[Dave WM]

well if the work the same as the stock calipers, then I would suspect the o ring that seals the piston.

[Zed Head]

36 minutes ago, Jaymanbikes said:

clearance between the pads and the rotors was perfect. I then bled the system and both fronts are sticking.

What do you mean by "perfect clearance between pad and rotor"?  I don't think that there's a clearance spec.

And did they stick from the start or after you drove it?  Do they stick so bad that they get hot and the car won't roll?  Or do they stick when you try to turn the rotor by hand with the car still n the air?

Need more detail.

[Jaymanbikes]

Perfect clearance meaning no rubbing on the pads.  Once I bleed them and while it was still in the air they were dragging a bit.  I then took it for a short drive 4-5 miles and they got worse, I started headed back and by the time I go back they were really hot.  They were then sticking so bad I could not even push the car at all in my garage. 

[Mark Maras]

If the pistons were removed, is it possible that the o-rings (not an o at all) were installed backward? They are directional. The bevel is designed to allow the pad to pull back from the disc just enough to maintain pad to disc contact. The slight contact is to keep the discs dry in wet conditions.

[Patcon]

My money is on a miss adjusted master not allowing fluid to return from the caliper

You could test by cracking a bleed nipple on the front circuit to release any pressure and see if that helps

Edited June 4, 2017 by Patcon

[Jaymanbikes]

My money is on a miss adjusted master not allowing fluid to return from the caliper

That's my guess, I am going to put my stock master back on tomorrow and see if it clears the issue.


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[Zed Head]

20 minutes ago, Jaymanbikes said:

 I then took it for a short drive 4-5 miles and they got worse, I started headed back and by the time I go back they were really hot.  They were then sticking so bad I could not even push the car at all in my garage. 

Sounds like you didn't adjust the booster rod to fit the new master cylinder, and the piston in the MC is pushed forward, blocking the fluid return hole.  A fairly common problem.  You need to remove the MC and shorten the booster rod.  Or shim out the MC.  Here's a picture from the FSM.  With all of the various aftermarket parts though, you kind of have to adjust by feel, or take measurements.  I don't think that their "B" length works for all MC's.

[Zed Head]

We're all on the same page.  If it was mine I might just build a shim, loosen the nuts and slide it in between the booster and MC.  Easy and same end result but you get to keep the new parts.

[Jaymanbikes]

We're all on the same page.  If it was mine I might just build a shim, loosen the nuts and slide it in between the booster and MC.  Easy and same end result but you get to keep the new parts.

What material would use for the shim?


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[Dave WM]

are you getting the specified free play on the brake pedal? I had a loose bolt that sets the stop point on the brake pedal. It would unscrew every time I applied the brakes, eventually limiting the return of the pedal to the point where the actually started to lock up.

[Zed Head]

Not ignoring you Dave WM.  He only talked about replacing the MC so the assumption, maybe wrong, is that he didn't mess with the inside stuff.

Another reason that I might use a shim is that several people have had problems adjusting the adjustment on the booster rod.  It tends to get stuck.  Sometimes really bad.

Fender shims might be about perfect.  You could loosen the nuts, let the MC push out to where you can just feel it touching the booster rod, then slip the fender shims over the studs and clamp it back down.  You can get a whole box of various thicknesses at Harbor Freight, and thye're u-shaped so that you can slip them without complete disassembly.  A little bead of sealant across the top and sides to keep water out and you're done.

Big picture, if it works but you still don't like the shims you can take it apart and do it "right".  At least you'll know what the problem is.