Brake Caliper Seals

I heard somewhere on YouTube, the brake calipers should be torn down, cleaned and rebuilt every season if you ride on track. I thought it was a little excessive, especially for my skill level. He also said that the heat will turn the fluid behind the caliper pistons to a varnish-like substance. I have seen this before when my dad and I bought an RC51. I don’t know if the brake fluid was ever flushed on that thing. The fluid in the reservoir was black and the fluid in the brake calipers looked like phlegm.

With the calipers already having two seasons on them, and my ‘21 R1 was getting a GYTR kit ECU and wire harness this off-season. I thought, I might as well tear’em down and see how bad they are.

Well, everything looked great. No varnish or phlegm-like substance behind the caliper pistons. There was brake dust build up on the outside of the pistons and dust seals, but that was to be expected.

Here’s where things got interesting. The OEM piston seals, from Yamaha, came with a thin film of red grease on them (Moly?). I was thinking the grease would contaminate the brake fluid. But maybe this was special grease compatible with brake fluid? Maybe it was just put on there so the seals wouldn’t dry out while sitting on the shelf? But the dust seals didn’t come with red grease on them! The diagram inside the Yamaha service manual shows to install them with brake fluid. Just like every other manual I have seen. So that’s what I did.

What’s up with the red grease?