Brake Lock-Up Question
05-09-2015, 02:18 AM
#1
Three Wheelin'
Thread Starter
Brake Lock-Up Question
I have an '86.5 928 track car, with 314whp, ~2800lbs, with stock (993 non-turbo) calipers and blank rotors (not slotted or drilled). Front pads are odd-ball Mintex pads and rear pads are unknown.
When the brakes and tires are cold, I find myself locking up the fronts, and occasionally the rears. As temps rise, in both the brake system and the tires, I can manage the issue with pedal modulation.
My question is, is the lock-up caused by lack up temperature in the pad/rotor, or lack of temp (and therefore grip) in the tire?
I've done 25-30 minute sessions at California Speedway, with only a bit of fade at the end of a session. If I were to auto-x the car, I imagine these pads (at least the fronts) would not be optimal.
I feel that the cold pad/rotor causes me to apply more pedal pressure to compensate for the lack of slowing, causing the lock-up. I know the obvious answer is to get the brakes up to operating temperature, but I'm strictly talking auto-x, which may take 2-3 runs, leaving only one solid run to lay down a decent time.
Am I correct in assuming that a pad that works in a lower temp range will properly slow the car with less pedal pressure, as the minimum operating temp is achieved sooner?
TIA
When the brakes and tires are cold, I find myself locking up the fronts, and occasionally the rears. As temps rise, in both the brake system and the tires, I can manage the issue with pedal modulation.
My question is, is the lock-up caused by lack up temperature in the pad/rotor, or lack of temp (and therefore grip) in the tire?
I've done 25-30 minute sessions at California Speedway, with only a bit of fade at the end of a session. If I were to auto-x the car, I imagine these pads (at least the fronts) would not be optimal.
I feel that the cold pad/rotor causes me to apply more pedal pressure to compensate for the lack of slowing, causing the lock-up. I know the obvious answer is to get the brakes up to operating temperature, but I'm strictly talking auto-x, which may take 2-3 runs, leaving only one solid run to lay down a decent time.
Am I correct in assuming that a pad that works in a lower temp range will properly slow the car with less pedal pressure, as the minimum operating temp is achieved sooner?
TIA
05-09-2015, 11:35 AM
#4
Frankly, I wouldn't run that equipment on a track, especially 7 year old tires. I consider myself a professional tightwad and I wouldn't run that setup nor would I expect to be able to sort it out by posting this question on an internet forum as there are just too many variables.
Put a decent set of tires and brakes on the car and retest. I would also at least check the rotors for sufficient thickness. For autox, I would think a decent street tire will do. For brakes, I'd get some autox pad recommendations. I don't autox, but I suspect you will want something that will work better cold. My PFC 08 track pads usually take a lap or two to get up to temp, which by then I would suspect an autox run is over.
Once known good pads, rotors, and tires are on the car, you can get to the business of sorting out the remaining issues. If you are lucky, the issues you are having will simply go away. I would think good autox tires and brake pads for the 928 is something already known. Maybe try posting over in the Autocross forum.
My $0.02.
-Mike
Put a decent set of tires and brakes on the car and retest. I would also at least check the rotors for sufficient thickness. For autox, I would think a decent street tire will do. For brakes, I'd get some autox pad recommendations. I don't autox, but I suspect you will want something that will work better cold. My PFC 08 track pads usually take a lap or two to get up to temp, which by then I would suspect an autox run is over.
Once known good pads, rotors, and tires are on the car, you can get to the business of sorting out the remaining issues. If you are lucky, the issues you are having will simply go away. I would think good autox tires and brake pads for the 928 is something already known. Maybe try posting over in the Autocross forum.
My $0.02.
-Mike
05-09-2015, 12:18 PM
#5
Three Wheelin'
Thread Starter
Thanks, Mike. I posted here because this is where the knowledgeable folks are.
I'm not trying to sort out my **** box on this forum, I was just trying to talk about brake pad/rotor temperature, pedal pressure and the resulting brake lock-up.
I'm hoping to get a better idea of WHAT makes a pad "work better cold." Is it simply operating temp range being lower?
If a pad that "works better cold" provides the same friction at a lower temperature as my current pad does at a higher temperature, given the same pedal pressure, then that's where I'll start.
I'm not trying to sort out my **** box on this forum, I was just trying to talk about brake pad/rotor temperature, pedal pressure and the resulting brake lock-up.
I'm hoping to get a better idea of WHAT makes a pad "work better cold." Is it simply operating temp range being lower?
If a pad that "works better cold" provides the same friction at a lower temperature as my current pad does at a higher temperature, given the same pedal pressure, then that's where I'll start.
05-09-2015, 07:24 PM
#6
Brake pads and tires all have an optimal heat range.
Street tires and pads must function at full capacity when cold... "track" pads and tires must function at high temperatures.... there's not a lot of middle ground.
Although technology has narrowed the gap, generally speaking what's good on the street is bad on the track and vice-versa.
For track, at a minimum, you must have high-temp racing fluid (DOT 4, or equivalent), "performance" street brake pads, and new, "high" "ultra" or "extreme" performance tires no more than two years old.
Street tires and pads must function at full capacity when cold... "track" pads and tires must function at high temperatures.... there's not a lot of middle ground.
Although technology has narrowed the gap, generally speaking what's good on the street is bad on the track and vice-versa.
For track, at a minimum, you must have high-temp racing fluid (DOT 4, or equivalent), "performance" street brake pads, and new, "high" "ultra" or "extreme" performance tires no more than two years old.
05-09-2015, 07:32 PM
#7
Trending Topics
05-19-2015, 02:37 PM
#8
ABS
I have an '86.5 928 track car, with 314whp, ~2800lbs, with stock (993 non-turbo) calipers and blank rotors (not slotted or drilled). Front pads are odd-ball Mintex pads and rear pads are unknown.
When the brakes and tires are cold, I find myself locking up the fronts, and occasionally the rears. As temps rise, in both the brake system and the tires, I can manage the issue with pedal modulation.
My question is, is the lock-up caused by lack up temperature in the pad/rotor, or lack of temp (and therefore grip) in the tire?
I've done 25-30 minute sessions at California Speedway, with only a bit of fade at the end of a session. If I were to auto-x the car, I imagine these pads (at least the fronts) would not be optimal.
I feel that the cold pad/rotor causes me to apply more pedal pressure to compensate for the lack of slowing, causing the lock-up. I know the obvious answer is to get the brakes up to operating temperature, but I'm strictly talking auto-x, which may take 2-3 runs, leaving only one solid run to lay down a decent time.
Am I correct in assuming that a pad that works in a lower temp range will properly slow the car with less pedal pressure, as the minimum operating temp is achieved sooner?
TIA
When the brakes and tires are cold, I find myself locking up the fronts, and occasionally the rears. As temps rise, in both the brake system and the tires, I can manage the issue with pedal modulation.
My question is, is the lock-up caused by lack up temperature in the pad/rotor, or lack of temp (and therefore grip) in the tire?
I've done 25-30 minute sessions at California Speedway, with only a bit of fade at the end of a session. If I were to auto-x the car, I imagine these pads (at least the fronts) would not be optimal.
I feel that the cold pad/rotor causes me to apply more pedal pressure to compensate for the lack of slowing, causing the lock-up. I know the obvious answer is to get the brakes up to operating temperature, but I'm strictly talking auto-x, which may take 2-3 runs, leaving only one solid run to lay down a decent time.
Am I correct in assuming that a pad that works in a lower temp range will properly slow the car with less pedal pressure, as the minimum operating temp is achieved sooner?
TIA
Have you disabled the ABS for the track? Or is the ABS the problem?
Greg