Sidney004

Had too much time on hands today so I did a little experimentation.

Typical long, soft pedal after a track day, did the normal routine; swapped rotors, flipped the PFC 99 pads(normal longitudinal taper, varied from .500 to .450 over the length of the pad,) measured and inspected the calipers(no spread,) bled the brakes(Motul 600, no air) and of course when I'm all done.......you guessed it, a long, soft pedal!

I'm the type of guy that drives my pads down to the bare metal, its just the way I am but just as an experiment, I swapped in a brand new set of pads(.560 thick from the backing plate.) Amazingly, the pedal is normal. Swap back, a different set of worn pads and ....... a long, soft pedal.

So, its not air in the lines, its not the master cylinder(no doubt, the one I replaced a couple months ago was good,) its not glazed pads; its either the normal, small longitudinal taper that is created in the 2 piston caliper or the pistons extending too far or a combination between the two.

I am going to be putting in pads that are worn down but not tapered(if there is such a thing on a 2 piston PBR) to see if its the pistons extending too far and a tapered set of pads with shims next.

The moral of the story is, if you are chasing after a long, soft pedal; start with installing a new set of pads.

brkntrxn

Good information

Sidney004

Did a little further "lab" work and its definitely the longitudinal taper that is causing the long soft pedal. A .030 taper was enough to cause it on my set of calipers.

Bill Dearborn

Yes, I found that out in 97 on my 97. First time at the track with the car. 2500 miles on the clock and the pedal got longer and longer. Dealer replaced the pads under warranty due to the tapering and pedal was solid again. Later on tried different braking method to reduce caliper that Ron Brown from GM Racing suggested. When applying brake push on pedal easily until pads are seated against rotor and then push hard. After that I started flipping pads from side to side to even out taper. Worn un tapered pads do not cause a long pedal. Long pedal can also be caused by a worn wheel bearing. I never really encountered a long soft pedal. It was always a long but hard pedal when the slack was fully taken up. Another way to reduce the issue is to pump the brake pedal with your left foot while still accelerating toward the next corner. That gets the pistons pushing the pads fully against the rotor just before you hit the brake to slow the car.

Bill

trackboss

Pad taper will do that. The worst pad taper I ever got was on some huge cnc 6 piston calipers. Brand new pfc pads. After a 20min race one end was full thickness and the other end was damn near down to the backing plate. Car stopped really well, but the pedal inconsistancy was horrible.