[dradernh]

Originally Posted by smchuck

I have not seen the seal in the photo in any of the rebuild kits I'm finding online. Can anyone clarify?

The OEM rebuild kit includes only the dust boots, and not the piston seals. I've assumed that BMW has decided that if an owner needs piston seals, he or she may as well replace the entire caliper.

Note that while the front and rear dust boots have different BMW part numbers (the fronts contain twice as many parts), they all have the same Brembo part number (20.4872.46). When I bought rear dust boots, they had to be ordered from Germany. I could have just ordered a third set of front dust boots and used them on the rear caliper pistons.

I had my shop measure one front piston, and it measured at 40mm. According to Zeckhausen, this is consistent with the Brembo dust boot part number. Given that all of the dust boots are the same Brembo part number, I've assumed all of the pistons on the car are 40mm. I suppose it's possible that could turn out not to be true, as I'm no expert in these matters, and we only measured the one piston.

Below are sources of piston seals and piston size cross-reference information that I've identified. I expect there's other info out there as well.

HRP World
https://www.hrpworld.com/bre-1055955...seal-each.html – Regular Seal
https://www.hrpworld.com/bre-1057224...re-seal-e.html – Anti-Knockback Seal

Ohio Performance Solutions
https://www.ebay.com/usr/ohioperformancesolutions
"These sets consist of HIGH TEMPERATURE HEAT RESISTANT, silicone gray
dust boots and HIGH TEMPERATURE pressure seals, designed for StopTech
and most late-model Brembo calipers.

These are the perfect components for street & track-oriented performance
vehicles!"

Zeckhausen
https://www.zeckhausen.com/catalog/i...h=82_1169_1170 – Piston Diameter/Brembo Dust Boot Cross Reference
https://www.zeckhausen.com/catalog/i...h=82_1169_1171 – Piston Diameter/Brembo Dust Boot & StopTech Pressure Seal Cross Reference