I’m running a ST-40 332 mm front brake setup that I installed about 15 years and about 120 track events ago. I rebuilt them about five years ago. Recently, I’ve been having issues with the pistons not moving freely in the bore, resulting in drag and excessive heat buildup. I rebuilt them again recently, but that didn’t help. I’m wondering if there may be some buildup of corrosion products behind the seal ring. I managed to boil my fluid at Road Atlanta early this week for the first time ever, so I need to do something. I didn’t want to start scratching around the groove with a pick or something and risk damaging the sealing surface.
Anybody else have this issue? Time for new calipers? Thinking of switching to the AP setup from Essex. I’m still running 17” wheels, so I can’t get too crazy with upgrades.
'95 M3 S54 Track Toy
'19 X5 40i M-Sport
'16 Cayman GT4
‘23 GR Corolla
I don't see any option but to disassemble at least one caliper to have a look. If the dust boots (assuming you're using them) have melted that will impede free movement of the pistons. High temp silicone rubber replacement boots are available from Zeckhausen Racing, see https://www.zeckhausen.com/catalog/i...ath=24_213_214.
If there's any surface corrosion on the aluminum pistons you can buff it off carefully with a dish-washing type abrasive sponge. Replacement ST pistons are also available. New ST calipers are kinda salty.
Neil
There was nothing obvious when I rebuilt them a few months ago. Pistons were like new, bores smooth and clean.
I was wondering if there is a rebuilding service out there with the proper tooling to clean out the groove and verify the ID. I didn’t see anything about rebuilding services on the Zechausen website. I’ve bought plenty of parts from them over the years.
'95 M3 S54 Track Toy
'19 X5 40i M-Sport
'16 Cayman GT4
‘23 GR Corolla
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