Brake caliper pistons not retracting
 

Evening all. Have a brand new manual brake setup from Wilwood. 12 1/2" with 6 piston calipers for the front and 4 piston rear. My problem is the driver side caliper pistons are not retracting when the pedal is released. Now, the outside pistons are but the inside ones are not. Wheel is hard to turn obviously. So I took off the caliper, disassembled it, inspected and cleaned the pistons and O-rings, put it back together with the caliper shimmed correctly, re-bled the entire system, stepped on the brakes and now I'm back to where I started. The other 3 wheels are fine. Any ideas?

That's strange. Wish I had an answer for you man.

Is the brake hose new? They can collapse internally trapping a bit of pressure. Otherwise, send it back to Wilwood and they will replace it if defective.

Did you use teflon tape on any of the line fittings? Could you have a piece of that tape interfering with the fluid - lots of pressure pushing but ZERO retracting and a little bit of that tape could retain enough pressure to hold the caliper out??

Is the caliper piston(s) "free" when you take it off the rotor and push the pad back? Is it still free if installed on the rotor and you attempt to push it back?

If it's not - I agree with Vegas - could be a defective piece.

Also -- make sure it's the pad/caliper that's the issue --- can you see the mounting bolts?? Make sure you've installed the right bolts -- I've seen them where they go thru the bracket and are interfering with the rotor. Could explain why it seems fine until you reinstall the assembly.

Am using braided steel line with no tape whatsoever. The outside pad slides out no problem, but the inside pad I have to pry out. The pistons are only about 1/8" sticking out on the defective side, the other side the pistons are flush with the caliper.
What causes the pistons to retract anyway? When you release the pedal, is a suction created to draw the pistons away from the pads?

Good question about the suction -- there might be a teeny amount - but it would be minuscule. The pad is generally just resting on the rotor and the flex of the rotor will push the pad back (we're talking really small movements here). New cars with fancy ABS brakes will sometimes have a feature where if you turn on your wipers they figure your brakes (rotors) are wet and they'll apply a small amount of pressure just to dry them off.

Sounds to me like you have a bad caliper.

Since it's only the one caliper that's acting up... otherwise I'd be asking you about your complete system - like your residual valve etc. And some Masters have residual valves built in.. but your other caliper is acting normal so we're just worried about the one.

The flex of the square O-Ring seal and the knock back from any rotor run out is what draws the pistons back. If it is easy enough to swap the caliper left to right then try that to determine if it is caliper or the system. (Are your bleeders and bypass easy to swap) Does your mount have shims to center the caliper? Sounds like you might be off center also. All this stuff is harder to troubleshoot when you have to rely on someone else to look and touch...

Good call Michael, the caliper should be centered on the rotor. It's not uncommon to need to pry on a brake pad to remove it. I'd check the center of the caliper and drive it.

That's what I thought the problem was at first, that the caliper wasn't properly shimmed to fit over the rotor. But it's fine. Unfortunately I can't swap calipers, it's a one size fit only system. I'll keep yall informed in case this happens to anyone else. Thanks for all the input!!