One more thought, soft pedal vs. low pedal

[cstreit]

I was just reading through some old technical articles on Rennlist and had a thought... Some of my braking problems were as much a "LOW" pedal vs a "soft" pedal. Often the pedal seems to be low and a pump or two brings it back and then it feels fine...

Now, often when I put the PAGID prange pads in the 993 rear calipers I have on the front, they require some grinding of the sides of the pad to fit well into the calipers... They bind otherwise and are often hard to get in. If I didn't gring ENOUGH material off, the pads could be binding and causing me to do that extra pump now and again...

Sound reasonable? Could this be related to overheating rears somehow?

[john walker's workshop]

sounds like a system that has to be bled, or a failing master cylinder.

[cstreit]

Master cyl is new... REcently replaced because I suspected the same thing.

System has been bled many times (sometimes 2-3 times per day at the track)... Some rogue air bubble?

This really only manifests itself after 7-8 laps... Either from system heat, or pad wear and improperly moving pads.?

[Jdub]

At first I was going to suggest that your caliper pistons are not fully extended, and thus you are pumping to get them there, but if this is only happening after you heat the brakes up, then I have to wonder if the heat is causing your front 'pads to bind up again and refuse to push out/retract effectively. I am certain you must have replaced your spring in the caliper (the cross-shaped affair held in by the pins) so that you have a good retraction device. A bit of 1000 grit on the faces of the spring where they contact the pad might help if they are rough, but this is just a guess.

So I guess I would pull a bit more off the edges of your 'pads so you know they not binding when expanded under heat, and tell you to pull the spring and just leave the pins in when you bleed the brakes: this can help the pad go to full contact for a harder pedal. After bleeding, check each 'pad in turn for any play, and rotate your wheel to note binding. If too much play on any 'pad, remove it, put in an old worn pad, rebleed to force the piston out, then pull a bit of fluid from the master cylinder and push the piston back into the caliper JUST enough to fit your new 'pad back in.

Hope this helps. Under track conditions I suppose anything can happen!

John