PFC Z54 Piston Pealing? Corrosion?

[spxxx]

So... Long story short, I bought this kit from a forum member and 2 of the caliper pistons are showing some degradation/"pealing".

At first I thought it was corrosion but it almost appears that there's some sort of high temp coating on the piston itself that's pealing off. I measured a 0.2mm smaller diameter where this issue is appearing (44mm original size).

Has anyone seen this happen to pistons?

[Davisca455]

Looks similar to galling that I've experienced with hydraulic linear actuators here at work.

Sometimes material pairs don't care for each other when they touch, so I'm curious if the piston bore in the caliper has similar markings.

[Adrian g.]

Looks like the coating on the piston is deteriorating. Question is why? Mine look completely normal. Perhaps you can buy new pistons?

[spxxx]

Originally Posted by Adrian g.

Looks like the coating on the piston is deteriorating. Question is why? Mine look completely normal. Perhaps you can buy new pistons?

Hopefully the seller is helpful and is willing to go that route as they're unusable in their current state. Just glad I caught it before install

That's assuming the pistons are still for sale from PFC. Anyone know if the ZR54 kit from the M235iR is the same design as the Z54 kit? I assume so based on the info I've found from PFC and Bimmerworld.

[jritt@essex]

OP,
That does not look like a coating coming off. To me it looks like debris got into the piston bores around the outside of the pistons. Sometimes during a pad change, the pistons get pushed back into the bore with dirt on them (this is why the pistons on a racing caliper always need to be wiped down prior to pushing them back in). If the pistons are pushed in dirty, the dirt on the sides of the piston is ground between the wall of the piston and the wall of the caliper. My hunch is that if you pull out the damaged pistons and shine a light inside the piston bore of the caliper, you're going to see matching scores/scrape marks.

If only the pistons are damaged, you can replace them with new pistons. If the inside of the piston bores inside the caliper body itself are damaged, the caliper is unfortunately junk. With that type of damage, the caliper likely won't hold good pressure. The gouges would allow brake fluid to slip past the piston seals. You'd get a soft brake pedal, and consistent brake fluid loss around the affected pistons.

Wish I had better news.

[RickyBobby]

You should fully remove the pistons and inspect the entire caliper to know what you're really dealing with. Those appear to have gotten seriously hot.

[spxxx]

Originally Posted by RickyBobby

You should fully remove the pistons and inspect the entire caliper to know what you're really dealing with. Those appear to have gotten seriously hot.

Yeah the seller from the forum agreed to take a return, just wish they were inspected before shipping to avoid this hassle/cost of buying a second set of calipers as a backup (which oddly also have a similar issue)
On that note, if anyone wants a set a Z54 Calipers with slight damage to the tips of the pistons let me know! They're no where near as bad as these but should probably be replaced too... Bad luck all around.

[RickyBobby]

That's why I bit the bullet and bought new.
Love my AP's (they totally eliminated knockback), but I haven't had them long enough to notice any pad taper. Then again, I swap pads for street and track so I'll rotate them to avoid any potential tapering issues.
Any of the top tier kits you're looking at will serve you well.

[spxxx]

Originally Posted by RickyBobby

That's why I bit the bullet and bought new.
Love my AP's (they totally eliminated knockback), but I haven't had them long enough to notice any pad taper. Then again, I swap pads for street and track so I'll rotate them to avoid any potential tapering issues.
Any of the top tier kits you're looking at will serve you well.

Yeah honestly my Stoptech Trophies are basically new since this rebuild with added 4lb knockback springs. Think I'm just going to keep them after this whole nightmare. Cheap pads, super light and zero pad taper...