Brake Caliper Piston Retraction
#1
Drifting
Thread Starter
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.
#3
Race Director
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?
#4
Drifting
Thread Starter
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....
#5
Rennlist Member
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.
#6
Drifting
Thread Starter
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.
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#8
Rennlist Member
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?
#9
Drifting
Just eliminating the simple stuff: Have you bled/flushed your brake fluid lately? Are all of your bleeders tight?
#10
Drifting
Thread Starter
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.
#11
Drifting
Thread Starter
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.
#12
Burning Brakes
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.
#13
Drifting
Thread Starter
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?...
#14
Drifting
Thread Starter
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.
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.