Brake problems

[mtpockets]

Subject: Brakes
Problem: No pedal until 3/4 the way down.

I experienced a gradual decline in braking on my second track run at TWS on Saturday. Limped in at almost the end of the session, I still had brakes but had to press the pedal almost all the way down or pump several times. After cool down, I checked the fluid level>it was exactly where it was before and not hot. No leaks. Where do I start trouble shooting this? Master cylinder? Brake booster? Car ran great the first session and nothing has changed since I ran it hard at Harris Hill in March.

[Z-linkCobra]

How were the brakes after they cooled off? And if you pumped them a couple of time did they get any better?

One way to diagnose would be to install pressure gauges on the brake lines. That would tell you what the line pressures were doing. A great place to start.

[Tommy]

My first guess would be overheated brake fluid causing bubbles in the system. The first solution is high boiling point brake fluid designed to handle the heat generated during track events. If you are already using that, I'd look next for unshielded brake lines running too close to headers and other very hot things. The next thing is to look for is ways to blow air on your brakes to help cool them quicker between applications. .. BTW, I always put in fresh brake fluid before every track day event. Most brake fluids attract water from the air over time and will boil it creating bubbles during hard brake use.

[Mac VABCH]

mtpockets,

I agree with Tommy. Did you have fresh brake fluid in the system? March is to long to expect fluid to do its job under track conditions if you are really working the brakes. Also agree that use the best fluid that you can afford. Either Castro SRF (very expensive) or Ate Super Blue and Gold. One addec benefit of the Ate is that you alternate between Blue and Gold then you know by the color of the fluid that you have all the old fluid out.

Just as a reference I have the stock E36 brakes using Performance Fiction full race pads with Castrol SRF fluid (I can't really afford to but I use it anyway) and I change the fluid just before every event if the are more than a week or so apart. Also I still have the original routing of the brake line unshielded and I've never had brake fad (knock on wood) yet.

[mtpockets]

I always bleed the system before a race. Backdraft uses DOT 5 synthetic. I use performance friction pads, SS braided lines, upgraded drilled and slotted rotors. I have run several Performance Driving Events, it was warm Saturday but didnt think I was pushing the brakes to their limit.

[Mac VABCH]

Dot 5 is the problem. I quite running that long ago. I dought that you have reach the limit of the stock brakes they where designed for a car the weighs over 3200ish lbs you have reached the limit of the Dot 5 fluid. Castrol SRF is the way to go. When I switch to it I asked Reg about the DOT 5 spec for the brakes. He said not to worry and run the SRF...

[Clois Harlan]

I agree with Tommy and Mac on the fluid. If you didn't spend $20 per pint your probably using the wrong stuff. Go with Motul or Wilwood racing brake fluid and I think your problems will be solved.

It took me awhile to learn this lesson but several years ago at Mid America Track outside Omaha the ambient temp was over 100 degrees and I couldn't get my brakes to keep from being soft the first day. I switched over to the Motul for the second day which was every bit as hot and my brakes worked like a champ.




Clois

[Bailey]

All good advice here. The SRF, or the Motul 600 are both excellent. I use the Motul because I am cheap. Bleeding the brakes before every track event is an absolute necessity, and the clutch too for that matter.
If you do a thorough, fresh bleed, I bet you will have no issue.
Cheers,
Richard

[mtpockets]

Well it's torn apart. Calipers taken apart, fluid drained, ordered Wilwood Hi Temp fluid. I'll keep everyone posted after I get it back together. Thanks for the suggestions and help. I'll be rolling again soon.

[Bailey]

Cool man, keep us posted.
Are you going to RandG with James this year?
Cheers,
Richard

[mtpockets]

Short version was a malfunction of the aftermarket drilled and slotted rotors didnt match well with the pads. System overheated, boiled the fluid. Put the stock rotors (freshly turned) back on, new pads, re-built the calipers, drained the system of the DOT-5, replaced with Wilwood Hi Temp DOT-4, all is good.

No RNG this year for me. I have two weddings, one in Sept, one in Oct, both out of town, too much on my plate. Y'all have fun and be safe.

[Bailey]

YIKES!!. Hopefully one of the weddings isnt yours!!.
No Run and Gun for me. Time for someone else to have a shot at trophies