Charley B

This past Monday while doing a track day at Thunderhill my brake pedal went to the floor near the end of the second 20 minute session. This was on the '88. I was told by an alignment shop last year that there was a drag on the right front that they assumed was from a warped rotor. I replaced the front rotors and pads recently. The ABS probe on the right front was a little chewed up. Dennis K helped me bleed the front calipers and we went back out for about 15 minutes before they began to fade badly again. After a cool down lap we came in and Dennis measured 450 degrees at the right front rotor and 370 degrees at the left front. I don't know what type of brake fluid was in the system, but I think dot 3 boils at about 400.
My question is should I just assume caliper issues or could the ABS system also account for the over heating on one side.

hacker-pschorr

I found your problem. Street fluid should never be used on the track. Upgrade to super blue before your next outing and upgrade the pads to something like Pagid Orange.

inactiveuser1228

I vote for fluid. I've had mine do the same thing - right to the floor! Real fun.

Jim bailey - 928 International

Brake fluid absorbs water and water boils easily. Stock weight S-4 will get brakes pretty hot on a high speed track so get good NEW high temp fluid some performance pads ,new pads are thicker and insulate the heat from the calipers.

Charley B

Given how uneven the rotor temps are, does it sound like the calipers should be rebuilt? There are plenty of threads re brake pads here, so I won't ask for specifics on that.

Jim M.

What bias valve are you running? Going from the stock 18 bar to a 33 or 55 bar will move more of the braking to the rear and reduce the temps on the fronts. I also second the comments on fluid and track pads.

Jim Mayzurk
93 GTS 5-spd

SwayBar

I would not recommend 55 bar for the track as under hard braking the back end can lock up and lose control, especially on a cool/cold day.

On the street it doesn't matter unless you get into a panic/thresh-hold braking situation where the rear can lock up again.

Charley B

The bias has not been changed from stock. My limited technical understanding leaves me befuddeled by the thought of changing bias on an ABS system.

WallyP

Some possible reasons for the difference in rotor temps:
- Sticking caliper holding the brake on.
- Swollen brake hose holding the caliper on.

Jack the front of the car. Apply the brakes firmly, then release. Turn each front wheel and see if there is any difference in how hard they are to turn. If there is, check these two items.

-Different pads, or different amounts of wear on the pads. Check for pad thickness and appearance. It can be difficult to determine what is cause, and what is effect...

Fix what is wrong. Bad brakes can kill you, on the track or on the street. Not something to ignore or take lightly! Get the good fluid.

Sorry, but to have a racer say that he doesn't know what brake fluid is in the system bothers me a lot...

GUMBALL

Did the pedal get progressively softer first, or did you get a "have, then have not" occurrence?
BIG difference. . !
How old was the fluid in the car?
When you bled your brakes, did you just bleed the fronts, or the whole system?
How dark was the fluid coming out of the fronts?? . . were there bubbles?

bjzorn

One thing I can suggest as well. If your using the original 19 year old rubber brake lines. change them as well to some DOT stainless steel ones.

But I agree change your fluid and check the calipers and see if one side is sticking.

Good Luck and be careful out there

Brandon J

Charley B

Wally - I'll follow suggested procedure for determining caliper health. Rotors and pads are new so I'm curious to see if there is any uneven pad wear. The fluid was changed when PO had brakes done but the work order didn't specify fluid type. I'm usually pretty **** about that but hadn't done my own flush for first track day.

Ken - There was a little fade before I lost the pedal but I was thinking normal for 15 minutes of some pretty agressive driving.
The fluid is about 14 months old.
We just bled the front calipers, I was manning the pedal and didn't observe the color or amount of bubbles. The pedal came back firm but after another 15 minutes I could feel some fade so I called it a day.

Brandon - I assume a minimum of fluid flush and caliper rebuild are in order but I guess I should give some serious thought to your suggestion re. brake lines.

GUMBALL

I'm not trying to be pedantic, just trying to make sure there isn't another problem hiding somewhere (with its own surprise). I am unclear what you mean by "fade". Did the pedal start to go soft, or did the pads seem to lose their grip? Did the ABS start to cycle? When braking hard, does the car pull to one side?

Excellent suggestions above. May I add a few:
> when pushing caliper pistons back, in order to replace pads, open the bleeder - you don't want to push fluid back towards the ABS pump

> when bleeding brakes, bleeding a front and a rear simultaneously allows full pedal travel, and allows more complete evacuation

> take a careful look at the brake pads, do they look "cooked" or "glazed" ? Do the corresponding ones look the same, and are they the same thickness? Do both front rotors look the same? A slightly more aggressive pad compound can lessen the time on the brakes, reducing the heat transfered to the caliper.

> In addition to ATE Blue brake fluid, AP 551 is equally good, Castrol SRF has the highest boiling point (though more expensive)

IcemanG17

Charley
Wally's suggestion should be quite telling about the cause of the problem....that plus a flush of super blue or gold should solve most of the problem.....I run super blue with no problems at all.....never had any fade issues even with stock (??) pads......I did notice that the outside pad on both my front brakes wears faster...but since its the same on both sides I'm guessing the calipers are working fine?

Charley B

Ken - Fade may not be the best word. It began to use more pedal for the same amount of braking. Then pedal to the floor, but one or two pumps gave me pedal, then even pumping gave me no pedal. This all progressed from turn 11 back around to turn six after which I got off the track.
I never noticed ABS on track, but testing in the paddock with say a fairly hard stop from 30mph gave me a lot of ABS pulsing. I thought I was getting a little lock up at the right front but Dennis tried it and thought it felt normal to him. The majority of my driving life was pre ABS, when threshhold breaking was monitored by your foot, your butt and you brain so to me ABS is still just a weird anoyance. I know, get with the times.
I didn't notice any pulling to one side when braking hard.
The current pads have less than 500 miles on them and I pushed the pistons back without opening the bleeders.
I've never heard of your bleeding suggestion. Are you saying an effective sequence would be; bleed master, bleed RF and RR inners at the same time, then outers together , then LF and LR inners, then outers and lastly, master again?