Ok here we go again with the brake fade stuff. 2014 gsxr-1000, have SS lines, stock brembo calipers, vesrah XX pads, have tried both a brembo 19x20 and an RCS, RBF600 fluid. The problem - after 5 laps or so the lever becomes very soft, it's still stopping but it doesn't have much pressure. When I pull into the pits the lever has no pressure at all, I push it and it goes straight to the throttle housing. Cools down and everything becomes decent again I've removed the calipers and drained them of all fluid, , drained the lines and master and started fresh and bled half a bottle of fluid thru the system and this is still happening. Is this a brake fluid problem or a caliper problem or a combination of everything? Short of replacing calipers I'm at a loss
Brand new, drained the system, put it all back together, opened the bottle and started bleeding. I'm wondering if maybe air is getting past a crush washer, I didn't replace them. However the brakes did this prior to taking everything apart as well so still not sure
Have you tried rebuilding the master cyclinder? I wonder if it's getting hot and there is just enough wear in the seal that when the bore expands it's allowing fluid past? I assume with your fluid change you're confident there's no air in the line, if it were caliper seals you would see the fliuid residue from it escaping, you have ruled out fluid, and air, sounds like lines are ok, but inspect for bubbles especially next time they are hot. Realistically there are 6 things, 1 pads 2 rotors 3 fluid (air in fluid) 4 lines 5 calipers 6 master cyclinder 7 ABS if applicable
IMO, either u still have some residual water / bad fluid in there or something metal is warping with the heat.
I had an issue where my caliper seals weren't pulling the pistons back properly, and it would overheat the fluid. It was just enough drag that you couldn't really feel it, but it wouldn't let the brake system cool in between braking zones. Maybe it's time to rebuild.
It's not a stock master cylinder, both have been brembo. I'll be looking into rebuilding the calipers and see if that helps.
Try Castrol SRF. I don't see how it would be a caliper issue, unless the calipers are visibly sticking. You said you removed the calipers and drained them of all fluid? Did you actually take the pistons out? If not, that might be a issue. Old fluid sitting behind the pistons that you will never really get out with bleeding.
Working off this list I think you can easily scratch off # 1,3,4,6. A visual inspection of pads is sufficient, you know knew fluid, lines I'd imagine are good as long as they havent internally collapsed which I know is an issue on cars, and you have swapped MCs. I vote to get some cheap used calipers and give them a try or just rebuild your current ones. What about checking rotor and caliper temp when you come in from the track. That could give you some good pointers.
Appreciate all the input, that particular bike is gone. I ended up installing a galespeed master and issues pretty much went away. So perhaps both of my other master cylinders were bad/needed rebuilt.
