Brake Caliper Piston Retraction

Would anyone happen to have a factory spec or reference for how much retraction is appropriate for each brake caliper piston? I know the piston seal should retract them some when brake pressure is released, but I need to know how much is too much.

From what I've seen, they only retract to flush with the caliper frame. How in the world are you getting them to retract more? Maybe contact a caliper rebuild shop.

I don't think he's talking about when doing brakes, but rather upon releasing the brake pedal under normal driving. The square seal is what provides that retraction, so I mean we should be talking a mil or less. Are you potentially suffering from pad knockback?

Quotes source post: 15639073

Yes that�s correct. I�m trying to determine if the Akebono Euro pads are slightly out of spec compared to Textars or if all of the pistons are retracting a bit too much. I think my next plan is pull each caliper individually and actuate the brakes with a piece of wood, just slightly thinner than the disc thickness, placed in between the pads. Then compress the pistons by hand just enough to allow the whole assembly to fit back onto the disc. I find it hard to imagine that all four calipers are retracting too much and are out of spec. But I�m trying to methodically knock out variables....

Calipers never "retract too much" without outside influence. Like mentioned the square cut seal provides a small amount of retraction, any other retraction is caused by rotor run-out, flexing of the rotor due to cornering stress, or worn/loose wheel bearings ect.

Quotes source post: 15639586

Understood. All four calipers and all 16 pistons are doing it. When the car is off and has been sitting for a bit, I can press the brake pedal and it goes nearly to the floor and I can hear all of the pistons contact the pads. If I do any subsequent presses after that, then the pedal is stiff and no noise is present. So it seems to me that the distance between the pistons and pads is a bit too far for where it should be.

Try to quantify the gap between the pads and rotors by inserting a feeler gage in the gap. Report back to the group.

So, when you pull into garage to park, brakes feel normal and car stops fine, but after sitting you get the "pedal to the floor" situation? If this is the case, that pretty much eliminates rotors, bearings, and even pads for that matter doesn't it? Master cylinder going?

Just eliminating the simple stuff: Have you bled/flushed your brake fluid lately? Are all of your bleeders tight?

Quotes source posts: 15640388, 15640405

I�m not yet convinced it�s the MC because successive pedal presses always stay firm. It�s my understanding that an MC with an internal leak would allow the pedal to eventually sink to the floor, no? Aggressive braking in the car has been solid thus far. To me, it seems that the first pedal push is what gets the pistons to reach out and touch the pads. Once that has occurred, then everything is normal again. I did a full flush and two bleeds. All the bleeders and lines are tight with zero leaks or seepage. The reservoir is topped up too.

Looks like they are all retracted from the pads by about 1/8� if you don�t account for the dampers. Maybe just under 1/8� if you do. Seems like too much to me.

That’s way too much. Pad gap is typically only about 0.008- 0.010 inch. There is no way the square seal could create that much gap by itself. Something in the system is either pushing the pads and pistons back or sucking the pistons back.

I�ve read that 914�s sometimes have an issue with needing to reset the �neutral� or retracted position of the pads. I wonder if I�m having the same issue?...

I take it back. I was looking at the piston seals and not the pistons themselves. There�s very little if any clearance between the pistons and pads. I undid the whole assembly and recoated everything in Cerami-Glyde and retorqued everything to spec. Will see if it has any impact. I did did notice that it looked like the pads have been moving against the cylindrically-shaped stops in the calipers. Not sure if that�s normal.