Brake Pedal Feel (not much!)

[Blue Streak 21]

I drove my car in it's first race this past weekend. Our Southwest Motor Sports Club held the two day race. The car worked well with the current set up and the scrub Hoosier Cup tires. I qualified the car on the front row (2nd) both days. The fields were small, but fun nonetheless. I came home with 2 second place finishes and a third. Had a good battle with my driving instructor on Saturday. We had several laps of nose to tail racing. His Vette was much faster in the straights, but I could catch him in the twisties. Great stuff.
I had two issues for the weekend. The foremost was the pressure needed to activate the brakes made modulation difficult if not impossible. I locked up the front tires many times into our hairpin. Speed is about 70 mph down to 35 mph for turn in. Initial bite is good, but the brakes lock in the second half of decel. I've got so much pressure on the pedal its impossible to "feel" when the brakes go into lock. To deal with the problem at lock up, I finally had to release all pedal pressure and just turn into the corner. I let understeer take off the last 5 mph. Not the way I want the car to enter this corner, but it was better than continuing to make the flat spots worse.
I'm wondering why this Brembo system has such high pedal pressure? Is it the pads (I'm using the PFC or stock pads)? Is it the orifice size in the master cylinder, and can this be changed? Do the series cars with the bias system seem to have this same issue with incrediable pedal pressures? I'm coming from a Z06 with power brakes (and ABS) so I'm spoiled.
I can't imagine students learning threshhold braking with this system. What did the school do?
The other minor issue I had was that the gas tank vent tube kept blowing gas onto the track on left had turns. They almost black flagged me during on session for the car leaking fluids. I added a catch can to retain the overflow. I increased the volume of the can to 1/2 gallon to catch all of the overflow. Anyone else have this problem?

[Gatorac]

My tank vent will spew some fluid occasionally. It may need a check valve installed in line with it. My SRF had one. You actually had to stick something in it to keep it open when adding fuel.

Installing master cylinders with a smaller bore would reduce pedal pressure. Different pads may make a difference too. Any changes from stock will probably require the addition of a balance bar to adjust front to rear bias. They are available for these pedal sets.

I was considering building a special piece of exercise equipment to get my right leg into shape.

[David Eastman]

I think you hit the nail on the head when you said you are coming from the Z06. I learned on a car with on power brakes and no computer. I find these brakes to be just fine.

David

[Squerly]

I haven't had any problems with mine either but maybe I'm just not driving it hard enough .... But seriously, I really like the feel of mine. I spent a good deal of time in a 930 Porsche and if you aren't careful you will find it easy to flat spot the front tires. (ask me, I know how to do it... )

I also have a 996 Porsche (with anti-lock brakes) and when I first started driving it I felt the computer taking over all the time. I eventually learned to drive it in such a way that I seldom ever feel the assist.

[NZGTRA17]

I have had the same problem with lack of brake pedal feel impacting on modulation. I have destroyed 2 front tyres as a result todate. I have yet to lock both fronts, mine has always been the front right (track related).

To overcome this we have now dialled in some additional weight bias onto the opposite front shock (a couple of turns on the spring perches).

Being stuck for a spare front to replace a damaged tyre at our last outing, we borrowed a pair of slicks and ran them on the front with Hoosier R3S04's. Seemed like a great idea, but before you know it I was looping the car due to imbalance in grip...........a lot of fun until another car is coming through on you.

I will look at both master cylinder sizes and fitment of a Tilton bias cable onto the existing balance bar in the GTRA to fix the brake pedal feel.

One thing to watch with the Tilton pedal box in our cars is the circlips on the ends of the brake pedal pivot point. When I received my car one of the circlips had popped off and the brake pedal was in danger of popping off the pivot which was half out of the pedal box. I have not only replaced the circlip but have also fitted a bolt (with large washers under the head and nut) through the pedal pivot to prevent it dropping out of the pedal box should the circlips come off again.

[panoz302]

Part of the issue is the pads, the PFC 97 stock pads have good life but bad initial bite, they are good for long enduro but not sprint on aggressive braking, the pfc 01 are much better for this car IMHO, and are the ones used in the GTS cars. why they initial bite is better with allows you to release and modulate going into the turn as opposed to staying hard in the pedal just to get your speed down, downside is they will not be as rotor friendly. As far as the pedals, cylinder go, I added omp pedal covers for a better surface to grip. I discussed the issue with several race shop who have gts experience, and a larger cyclinder might help and or changing the pedal assembly to get a better mechanical advantage. I have spent some time doing threshold braking and am running Perrili D3 slicks ,and the brakes will lock up but it takes alot of pressure and I also find these pads need some heat to work.

[Blue Streak 21]

Thanks for the suggestions. I think I'll try some more agressive pads when I change them next time. I think that initial bite would help some. I also will try to reduce the pedal pressure some. I think feel will come easier with reduced pressure. Otherwise I may have one ripped thigh, and one chicken leg at the end of the race season.