Experienced significant fade

#1

Ran the VIR full course Monday with 1 fresh ATE 200 fluid and new Cobalt Friction XR1/XR3 setup. By third session at the end of the front straight there was some pretty significant fade which would resolve by turn 3 (granted not braking nearly as hard) and would not exhibit itself at the end of the back straight only to show up again at the end of the front straight. Does this sound like an overheating issue, a fluid issue, or maybe a pad issue?

#2

Lots of folks are using that fluid so can’t be that. Most folks have brake cooling set up in front, but not everyone does, and VIR gives you lots of time for brakes to cool. I don’t know anyone running those pads tho, so that would be something to check into.

Odd that there was the symptoms were only on the front straight tho. That’s hard to explain. There’s plenty of time before turn 1 for the brakes to cool.

#3

That’s what I was thinking. Odd at end of front straight. I am going to rebleed the brakes and see if any air comes out. Do you have an opinion as to whether or not a component of the brake system other than pads and fluid may be involved?

#4

The feel of air in your brake lines is very different from fade. Don’t chase a symptom that doesn’t exist.

Brake fade should feel like…your pedal is as hard as usual, but your car doesn’t do as much stopping. As a result you push hard as hell, but the car still seems low on stopping power. This is usually a matter of the pad being force to operate outside of it’s design temp range.

If, on the other hand, the brake overheat boils your fluid, then you’ll have all sorts of air in the brakes. I don’t recall tho, ever hearing of a case where a SpecE30 had a convincing story re. boiling his fluid.

Re. other things involved. Well, strange things do happen. Sometimes you’ll just plain ol’ never get down to the bottom of what the hell was going on. At Sebring last year I had a helova time getting my car to stop. I convinced myself that my front calipers were not clamping as hard as they could. I got some gauges and fittings and spend 2 months testing brake psi at various places, replaced the MC 2x, and replaced the ABS pump 3x.

I spent weeks up to my elbows in brake fluid, doing every test I could dream up with over and over. I had gauges all over the brake system. For quite a while I was pretty sure that I was on to something, only to find that one of my hydraulic lines I’d had made for the gauges was partially plugged.

In the end, I didn’t find out a goddamned thing. Once I worked thru all my problems with the gauges, fittings, hoses, and pipes that I’d bought and made to do my testing, the damned symptoms disappeared. No matter what I did, suddenly I couldn’t reproduce the symptoms. I don’t know wtf was going on at Sebring.

But at the next event, the car’s brakes seemed ok.

Sometimes weird shit happens.

#5

OK spoke with Andie at Cobalt. He said it sounds like there may be a little pad displacement going on and to try a tap tap tap on the brake pedal as I go down front straight after cresting the hill to get the pad and caliper in proper position so when I apply the brakes for real the pad will be in right spot for the piston.

#6

If the problem goes away, it won’t because you tested the brakes before hitting them hard. It will be because sometimes, problems just inexplicably go away.

I would stick with pads that are in more common use. On the East Coast that is probably:
PFC 01, 06, & 08
Hawk DTC 70, & HT10
Carbotech XP 10, 12 and 14.

Some folks have strong feelings about pads. I don’t. They will all stop the car. I think that PFC is the most popular. HT10’s will kinda lose chunks of material towards the end, but they are cheap. Carbotech has a nice range if brake torque #'s available, but they fasten their pads on with rivets so you end up loosing a couple mm of available pad thickness.

#7

Well in any case thank you for your input!

#8

Don’t use the brakes so much.
Add cooling ducts.
Brake fade at the end of a long straight…yep that is where it happens, see comment #1

Just wait till you go to CMP (with the old configuration) in July.

RP

#9

Perhaps I’m a moron.

With that little detail made clear, I’ll share my story. I had very similar symptoms my first season in the E30, except it seemed more random. Occasionally, in any given braking zone the car just did not slow down like I expected. Pedal felt fine, but the brakes just wouldn’t do their thing. Next corner, all would be fine. Very frustrating, and I went off more times than I care to remember. Finally figured it out… The E36 I was coming from has a very low brake pedal, and in order to heel/toe, I cheated my foot way to the right edge of the brake pedal and did all sorts of weird twisting to blip the gas. In the E30, the pedals were much better, and heel/toe was a breeze. It turns out, though, that I was still cheating my foot to the right side of the brake pedal. Sometimes it was just a tiny bit too much, and my big ol’ clown foot would catch the gas while braking. 150 HP ain’t that much, but it’s enough to significantly change your braking distance. Perhaps you’re a moron also? These pedals are pretty close together…

Cliff

#10

I’ve never had brake fade at VIR, Summit or NJMP. I don’t have brake ducts. I once ran brake pads until this happened:
World’s most worn out brake pads
Still no fade. Didn’t stop quite as well, but surprisingly still slowed the car enough I didn’t think there was anything much wrong.

Your problem lies elsewhere.

#11

I think “fade” was a poor choice of words. I have experienced fade from overheated brakes on heavier cars and it was the classic pedal sinks to floor and nothing happens. This was more of a pedal travel went further than normal on initial application of brakes and when I quickly released a little and reapplied pressure the brakes worked fine. I did some more research online and found that a bad wheel bearing can cause pad knockback among other things. Replaced one front wheel bearing this year already but need to check other one. My theory is that going through hogpen in a more “aggressive” fashion may have caused some pad knockback and this is why was only experienced at end of front straight.
I posted this to see if anyone else had experienced this phenomenon before.

#12

I should add that the heavy car episode was boiling brake fluid. I have yet to experience pad fade from exceeding the thermal threshold of a dedicated racing brake pad. But if this is indeed the case I would think the pads would do same thing at the end of the back straight as well since my braking effort is very similar between the two.

#13

[quote=“Diggs” post=82626]I think “fade” was a poor choice of words. I have experienced fade from overheated brakes on heavier cars and it was the classic pedal sinks to floor and nothing happens. This was more of a pedal travel went further than normal on initial application of brakes and when I quickly released a little and reapplied pressure the brakes worked fine. I did some more research online and found that a bad wheel bearing can cause pad knockback among other things. Replaced one front wheel bearing this year already but need to check other one. My theory is that going through hogpen in a more “aggressive” fashion may have caused some pad knockback and this is why was only experienced at end of front straight.
I posted this to see if anyone else had experienced this phenomenon before.[/quote]
Old description sounded like fade. New description isn’t fade, but could be knockback as you described.

Knockback is pretty darn rare, afaik. It gets claimed every once and now, but rarely proved. A bearing would have to move a helova lot in order to cause it. A rotor could be installed wrong tho. Debris can get in there and cause the rotor to turn off-axis. One of the 4 slaves needing to move farther then the rest would be enough to the pedal soft on it’s first push.

Pedal soft on first push could be MC too. Sure, that doesn’t fit the symptom of “front straight only”, but no cause really fits that symptom very well. The only difference in the front straight is that that it’s shorter and it starts with a long right turn (right drift and right sweeper at roughly same steering angle) instead of a short and slow right turn (Oaktree). If it’s knockback, it’d be pretty hard to come up with a theory that is front straight only.

Of course, things don’t always makes sense. Some problems and fixes are real head-scratchers.

#14

Check the slides on your calipers.

#15

I will do that. Replacing the wheel bearing and even thought the calipers are new remans with new guide bolts I will regrease them and see what’s up. Thanks.