If the calipers need to be rebuilt again you'll just need new seals, the pistons are fine to reuse.

BUT, I would start with bleeding the ABS. if there's air trapped in the module it's an absolute nightmare to get it out. Definitely consider dropping the $50 on a power bleeder, it saves soooo much time bleeding and you can do it all yourself.

 

Pretty sure you aren't suppose to double stack shims. Also bleed with the car running. The booster puts some pressure on the master that can cause problems if you bleed with the engine off. Napa sells a gallon of dot 4 for like 30 bucks, might wanna start using that to bleed till you figure it out.

 

how much should pistons pull back when releasing brakes? i'd assume not very much?

i have a power bleeder - are you talking about like the motive? pump it and crack the abs module lines?

yeah i'll try pulling them but figured it wouldn't really do much. i'll try though. hadn't heard of bleeding with the car on, could give it a shot.. may be pretty foul after a few minutes in the garage though

 

Yes, motive bleeder. Usually there's a factory procedure on how to properly bleed the abs module. Might be able to find it published in the shop manual.

The pistons only get pushed back by the rotor, the pads still stay in contact with the rotor for the most part. Are you sure you're not experiencing pad knockback?

 

i'll try bleeding abs. no knockback, i was just responding to sean's comment

 

Yeah, it's a minute amount. You won't really see the piston move. But even with the brakes released the pad shouldn't be super loose between the piston and rotor.

 

right, they're not.

 

so i've removed the shims and no improvement. i've got new pads & rotors waiting in the wings if it's those.

i noticed a small leak on the passenger's front ss lines at the caliper connection. i've tightened them down a little, and reflushed in case that introduced any air. there was a small improvement at the end of the pedal, so that it holds firm at the end, but the top inch or so still seems very soft & mushy. i may replace the lines (AMS ss) in the front anyway, always had good luck with the stoptechs. the 9 to X lines should be the same right? after the pads and rotors are replaced, that is everything except getting the calipers rebuilt. the pistons and all of that seems good, but i could try putting a clamp on the calipers to see if that helps - that said, i feel like if the calipers were flexing (significantly to cause soft pedal), i'd feel that at the bottom of the pedal where pressure is high, not the top half inch to inch of travel

also, has cracking the abs module open actually worked for anyone? i'll try it tonight, they practically seem seized but will go at it

 

Mushiness at the top of the pedal but having it hold firm at the end indicates excessive piston pull back to me.

 

what causes excessive piston pullback

 

Caliper seals and/or dust boots are smoked.

 

all right. caliper rebuild is on the list.

 

additionally, i'm not sure why the dust boots/seals would have failed so quickly; i've been using ti shims, bigger rotors = larger heat sink, haven't had any fade or boiling on track since. ti shims + vented ss pistons, larger x rotors with dba5000 floating 2 piece rotors.. done a good deal when it comes to heat management, everything but actual ducting at this point. idk that other people are having their seals fail...

still will also try a few other things before that, but will get the calipers rebuilt.

 

Have you tried removing ALL of the shims. You shouldn't need shims at all with the stainless pistons. And even slightly warped ships can cause a mushy pedal.

 

i removed the fronts but not the rears; figured the rears wouldn't cause much pedal feel, but i can remove the rears too if you think i should.