Brake Troubleshooting

What Can I Do About Brake "Shudder"?

[KS] I used my NSX mostly for three to five track weekends a year, 1991-1996. The first three years I had the car, I never experienced the brake shudder. The following three years, I experienced the shudder, and went through cycles lasting about four track events. I would start out with new rotors, by the second or third track event I would start feeling the shudder, by the fourth the shudder would be very bad, after which I would replace the rotors and start all over again. This was with stock rotors and pads.

 Before my last track event last year, I made a number of changes: 

  1. I switched to Stillen cross-drilled rotors.
  3. I switched to high-performance brake pads (several different kinds, in sequence, all obtained from RM Racing).
  5. I switched to Motul 600 high-performance brake fluid.
  7. I made sure the brake fluid was flushed at the start of the year. Previously I was not fastidious and was only flushing every several years.
  9. I made sure that all the sliding surfaces were lubricated when the pads were changed. I had previously done some of the pad changes at the track, without additional lubrication other than the anti-squeal goop on the back of the pad.

Since then I have driven one track event last year and six more track events so far this year and the shudder has not reappeared. IMO this is sufficient time to conclude that the problem is cured (or at least that it will not happen with anywhere near the frequency as it previously had). I am hesitant to point to any one change and conclude that that was the sole reason for the cure. But I don’t have the patience or desire to undo each of these five changes one by one to find the culprit. For that matter, it could also be some combination of these factors.

How Do I Diagnose Bad Brakes?

[BSD] Noises from brakes do not necessarily mean things are wrong or broken. In fact, noises from materials in friction with each other is expected and brake designers have to work hard at making them not make noises.

Some pads, usually the mid-range performance pads, seem to leave deposits on the rotors from extreme use. Performance Friction’s "black" or "HP" pads do that if you really work them over. The deposits on the rotors tend to build up and, after the event, it feels like the rotors are warped. The Porterfield R4S pads leave deposits on rotors, too, but they (the pads) wear the deposits off, again, once back to normal street use. This is a "feel" issue as opposed to a scratching/sound issue.

I used Porterfield R4 race pads at my last event. These pads always make a grinding sound and also screetch. Their purpose, though, is to stop a heavy car in a short distance before entering at turn, as opposed to quietly slowing the car before entering the parking lot. When I swtiched back to my street pads, _they_ initially made a screetching sound as if the pads were worn away and the backing plate was rubbing. This could not be the case, though, as my street pads were almost new when put on and I did the work myself minutes before.

After a day of driving, things get back to normal. (IE normal sounds from the brakes.) In my experience, street cars used on the track tend to lead to unusual sounds and other unexpected things (like melting brake piston boots). However, much of the time, the brakes aren’t broken, just in a state different than the normal grocery getter state.

If you suspect your brakes do have a problem, there are a few things you can do to verify things are ok:

  • Do a 40-0 medium effort stop with your hands off the steering wheel. If you stop straight, pass.
  • Check your pads for wear. If you have material on all four corners and it is wearing mostly evenly, pass
  • Check your rotors. If there are brake pad deposits on them, then ignore sounds and warped rotor feelings for a few weeks of normal use. If there are no deposits, check rotors for minimum thikness and warping. Check for cracks. Small surface cracks are ok, but if you can get your finger nail in them, then you might want to think about turning or replacing the rotors.
  • Check brake lines and calipers for leaks. There should be 0 leaks.

Funny sounds, particularly just after an event, usually means your system is working its way back to normal.

Your mileage may vary.