Losing brakes mid race?

I'm having issues with my brakes during the race.. at the start they're good but if we go 10-15 laps straight no matter what kind of track I'm on I'll lose em. ( pedal goes straight to the floor) but soon as a caution comes out or the race is over and I slow down the pedal comes back and I have brakes. Can anyone tell me what the issue is? I'm not heavy on the pedal at all. At most it's a tap or a Lil drag of em. Nothing major! I've changed fluids, bleed em anything I can think of and still have the issue!? Any help is appreciated!

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Originally Posted by racert22

I'm having issues with my brakes during the race.. at the start they're good but if we go 10-15 laps straight no matter what kind of track I'm on I'll lose em. ( pedal goes straight to the floor) but soon as a caution comes out or the race is over and I slow down the pedal comes back and I have brakes. Can anyone tell me what the issue is? I'm not heavy on the pedal at all. At most it's a tap or a Lil drag of em. Nothing major! I've changed fluids, bleed em anything I can think of and still have the issue!? Any help is appreciated!

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Sounds like you have a high spot or something in your lines causing an air bubble in the lines. No amount of bleeding will get this out. If the tallest spot in the braking system is NOT the master cylinder, you'll have problems like this. If it is a small bubble, the pedal might feel pretty good with colder fluid but as soon as heat hits that bubble, it becomes worse. Just be sure that there is NO point in your brake lines that is above the master cylinder. Other than that...I don't know...but that's what it sounds like.

Quote:

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Originally Posted by racert22

I'm having issues with my brakes during the race.. at the start they're good but if we go 10-15 laps straight no matter what kind of track I'm on I'll lose em. ( pedal goes straight to the floor) but soon as a caution comes out or the race is over and I slow down the pedal comes back and I have brakes. Can anyone tell me what the issue is? I'm not heavy on the pedal at all. At most it's a tap or a Lil drag of em. Nothing major! I've changed fluids, bleed em anything I can think of and still have the issue!? Any help is appreciated!

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Two thing come to mind:

1. You said you changed fluids, but: Either moisture in fluid or not a high enough boiling point.
2. The pedal is adjusted so the piston isn't fulled returning to the seated position. Make sure the rod to the M/C cup has least some slack in it and isn't slightly holding the plunger in just a little.

Make sure you have wilwood EXP or better for fluid. Using junk like Wilwood 570 I had brakes fade just touching the 3 wheel brake at each end of a big sweeping half mile. Since using good fluid I've never had fade again.

I just use off the shelf Dot-4 and have never had problems, but regardless, would a fluid issue resolve itself that quickly (at least according to the post)? Liking to think outside the box, a rotor with a good amount of runout (highspot) would push the caliper pistons back in and most likely wouldn't recover at race speed, but once slowed down it might. But it'd have to be a significant amount of runout.

To not make assumptions, do you have four piston, fixed (mount) calipers?

We had a chronic brake problem once.We had routed the lines in a way that you could not get all the air out of them.I route all the lines with a steady downhill flow,no loopes or dips, now.

you have a bent caliper mount, or loose hub.... the rotor is knocking the piston back into the caliper. or the caliper is hitting a spring or bar.

Stock Car Driver nailed it. My bet is loose wheel bearing once it's up to temp. It's ususally the RR. check right after u get into the pits

had the same issue couple years ago, like SCD and victory said , mine was a broken rr axle tube and the rotor was kicking the pads back

I have had same problem before, could get 8-10 laps in and loose pedal. My problem was a brake caliper piston seal was damaged and would aerate the fluid. If this is your problem check your brake temps, you will find the problem caliper. It will not have as much braking heat to it.