I have a strange phenomena with the front brake. After a session at the track and hard brake use, when the bike has been standing in the pits for half an hour or so, the first time I squeeze the brake lever it goes all the way to the bar. I have to pump it a few times before the pressure point is normal again.

During the ride, the brake is consistent, no fading, and the pressure point is the same all through the session. The brakes are standard, with new fluid and new pads. It's like the pistons in the calipers are creeping out when the brakes cools off. Very strange.

 

you bleed the brakes recently? I'd imagine you'd notice if the fluid was leaking out

 

No leaks, and I did bleed the brakes before the last trackday. It's not an issue when riding on the road. The brakes must be used hard for it to happen.

 

could it be a faulty MC? I replacd mine a few months ago ant the brake feel is much better

 

Could be but then it would not be dependant on the temperature. For this thing to happen the brakes must be used hard, the brake discs are really hot when I come in after one session. So I think it must be something down at the calipers.

 

Ive seen brakes that get extremely hot have the pistons pull back into the caliper while they cool. You have to remember, everything is getting extremely hot. The pads, the calipers, the fluid, the lines.... everything. And, everything has a different cooling rate. I don't know if the pistons in your bike are stainless or aluminum, but if they are aluminum, they will more than likely be pulling away from the rotor when they cool.

I don't think you have air in the system, I think when you pump the brakes, your just getting the pads back close the rotor they pulled away from while cooling.

Next time, have someone watch the pads and see how far away from the rotor they are. Pump the brake and have them check to see if the pads are indeed moving back into normal postion.

Or, take a feeler gauge and see where the pads are before you make your run, then check them again after your run and the bike has cooled. Im guessing your going to see you pads a good amount more away from the rotors. If your more than .020-030" further away... I'd say thats your problem. Also, I would check both calipers, and both sides of the rotor. You may only have one caliper creeping back, so make sure you check it all. And also, if each pad is say .010" away, that would actually be .040" total. You'll have to add it all up. Remember, a full pull on the lever does not move the pads much at all.

 

Thanks for the reply. I will check it more closely next time on the track. I guess it's not a big deal after all since the brakes works fine throughout the session. I just have to remember to pump out the brakes before going out (I did forget once last time which gave me a little "moment" in the first corner). I would like a little more initial bite but that's down to pad choise I reckon. I have "Braking" pads now, any recommendations for pads?

 

Im not really sure what pad to suggest as I've always ran factory replacements. The reason I do this I don't spend much time on my brakes, and factory pads are about the best pad you can use on the street as they don't require heat to work at their best. they are the best for initial response. But, the downside to factory pads is they transfer a lot of heat, and if your on the brakes a lot, you will get brake fade pretty quickly.

If your on the track quite often, then upping to a specific race pad is probably the best thing you can. However, just know that they don't work at their best until you get some heat into them, so a cold set of race pads will not grab as good as a cold set of factory pads, but after a few brake applies, the race pads become better than the factory pads.

One thing you can do to improve feel is get a set of stainless braided brake lines. They don't swell like factory lines do, the resist heat better, and give a much steadier feel while the brakes are getting hot by not expanding like oem lines do under stress.

I did forget to mention one other thing. Next time you on the track, after your cooldown and your feeler gauge check, pull the calipers and inspect the piston seal. Make sure you don't have any wetness or signs of leakage, such as grime build up around the seal. If there is, you may have a leaking piston seal.... which could also cause your issues. but it may only leak a little when its cooling down, but still a sign the seal is going bad and should be replaced.

 

if my f4 track bike was doing this, the last place you'd find me would be on the track. You're just setting yourself up for a wreck.

I highly doubt your pads/pistons are moving on their own.

I'd start with the master cylinder. How's your fluid level in the resevoir?