Replacing Dust Boots/Seals - Pad Knock Back - Track Use?

[Powerslide]

I have tracked my current F80 about a dozen times since 2018. The last time I tracked it (back in late summer 2021) I noticed long brake pedal travel a few times - so I stopped with that session (not realizing it was most likely pad knock-back - which I understand is remedied by doing a quick tap on the brakes right before the braking zone leading up to a turn - so I didn't get a chance to try that).

HOWEVER - I also know that I may have boiled the brake fluid (I now have stainless steel brake lines and will be replacing the fluid before the next track session).

I have a track session coming up in a few weeks - and I'm concerned about further issues with long brake pedal travel once the brake/fluid temps rise (no problems with long brake pedal travel on street since last track session) - so my question is - is it necessary or advisable to "rebuild" or replace the dust boots/seals, caliper pistons or anything else (again, about a dozen full days of tracking since 2018 - car has been daily driven since 2017 with about 51,000 miles)? I'm not sure such a caliper "rebuild" or replacement of these parts are necessary to avoid further problems with long brake pedal travel on the track - but I figured a good number on this forum can give some solid advice on this. Thanks,

[drroc]

Change the fluid with something like Motul 660 or maybe something even more expensive. Remove the pads and take a look at the dust boots. If the boots have totally cracked away, then it would be good to replace them. Also check the pad wear. If the wear is more V shaped, then possibly the piston seals are going out and hence cause uneven piston travel and retraction. Also if the calipers are still blue, then probably just a change of brake fluid is sufficient.

[Powerslide]

Originally Posted by drroc

Change the fluid with something like Motul 660 or maybe something even more expensive. Remove the pads and take a look at the dust boots. If the boots have totally cracked away, then it would be good to replace them. Also check the pad wear. If the wear is more V shaped, then possibly the piston seals are going out and hence cause uneven piston travel and retraction. Also if the calipers are still blue, then probably just a change of brake fluid is sufficient.

Thanks! How about if my calipers have turned that dark green color that everyone talks about on this forum?

[jfritz27]

I'm not sure if worn boots/seals would necessarily give rise to the symptom of long pedal travel. If a piston were seized, then certainly reduced stopping power...

If your boots are visually toast then it would be a good idea to rebuild them. I recently did this for the fronts using the high-temp seals kit from racingbrake. If you've never done this before, be warned that the brakes can feel a bit funny in the period right after, including some of the symptoms you're describing (initial longer travel). I believe this is due to the fact that the stiffness of the new boots tends to pull the piston back away from the pad (akin to pad knockback). "Exercising" the brakes for a couple hundred miles will help, and obviously they will eventually wear in and feel normal. It's something to be aware of if you decide to do this like a week before a track day, because as a result you may not have the confidence you're looking for until they fully wear in. I think mine took a couple weeks of street driving.