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Old 11-22-2006, 09:41 PM   #1
e36 323ti
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Default Brake pedal travel before, during and after track day events

I guess some of you attend track days with your ti's. What I and others have experienced is that after some hard laps the pedal starts to get low (even with braided lines, new pads, fresh fluid and slotted rotors). The brake performance is still good, but the pedal travel is longer than usual. After the track event it goes 2-3 days with normal driving before the pedal travel is normal. This happens with stock brakes and several brands of pads.

This has nothing to do with boiling fluid or brake fade.

Have you track junkies experienced anything like this?
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Old 11-23-2006, 12:07 AM   #2
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You need to bleed the brakes after every track session, if you want to keep brake performance at peak. You should also check the dust seals on your calipers for baking. The rubber parts of the caliper do get baked hard on track, sometimes after a couple days the rubber soaks up enough fluid to soften them and they work better.. But if I'm tracking a street driven car I'm going to regularly tear the calipers apart and replace the O-rings, and the dust seals.
The dust seals are optional on a track only car, I don't even install them on race cars.(They just bake away anyhow...)

Aslo when you change your brake pads, and your compressing the calipers, open the bleed screws so
you don't force grungy fluid back into the ABS pump and master cylinder. Instead just let it run out the bleed screws into a catch bottle.

later
Dave
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Old 11-23-2006, 03:26 AM   #3
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I can go almost 3 weekends of driving schools on Ate brake fluid.
My pedal has never gone down. I might start to get brake fad on the 6th day though.
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Old 11-23-2006, 04:57 AM   #4
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Fade means your way beyond what the fluid should be taking.

Its a minimum of once a day when on track.

The fluid is deteriorating each time it gets over 3 or 4 hundred degrees. If your going into any braking zone at over 120 your at the fluid limit for temp in about 2 laps.

I've used ATE but find the Motul lasts as good and is about 1/2 the price. That or buy the "special" ford truck fluid which is essentially ATE super blue in a ford labeled can if the MSDS is any givaway....

AS I mentioned before you want ot keep an eye on the dust seals because when the dust seal starts cracking you have also likely cooked the caliper piston o-ring. When it gives up brakes no worky worky......

Of course I'm usually working on rental cars and I do not want the customer having brake problems. If it was me Its my call....

Dave
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Old 11-23-2006, 05:09 AM   #5
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Quote:
Originally Posted by pdxmotorhead View Post
Fade means your way beyond what the fluid should be taking.

Its a minimum of once a day when on track.

The fluid is deteriorating each time it gets over 3 or 4 hundred degrees. If your going into any braking zone at over 120 your at the fluid limit for temp in about 2 laps.
Like I said, I start to get some fade on my 6th day.
Minimum of once a day when on track? Sorry, but that is just overkill unless it is very hot out and you are running solid rotors. Maybe you need brake ducts?
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Old 11-23-2006, 05:32 PM   #6
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Quote:
Originally Posted by pdxmotorhead View Post
You need to bleed the brakes after every track session, if you want to keep brake performance at peak. You should also check the dust seals on your calipers for baking. The rubber parts of the caliper do get baked hard on track, sometimes after a couple days the rubber soaks up enough fluid to soften them and they work better.. But if I'm tracking a street driven car I'm going to regularly tear the calipers apart and replace the O-rings, and the dust seals.
The dust seals are optional on a track only car, I don't even install them on race cars.(They just bake away anyhow...)

Aslo when you change your brake pads, and your compressing the calipers, open the bleed screws so
you don't force grungy fluid back into the ABS pump and master cylinder. Instead just let it run out the bleed screws into a catch bottle.

later
Dave
Here is what a Belgian brake engineer writes:

The one-time longer pedal travel you experience the first braking manoeuvre after a quick run is caused by the brake pads getting retracted from the hot brake disc (by a rubber inside the caliper). This is what is supposed to happen, otherwise your brakes would be dragging during driving. Next thing that happens is the brake disc cooling and getting thinner a couple of fractions of a millimeter. The slightest difference between disc and pads creates a long pedal travel. (someone should calculate the travel ratio´s to have some impression, or you could try putting a thin feeler guage between your pad and disc, retract it and press the brake pedal, you´ll notice the longer travel)

The extra effort is simply caused by the lower friction of the pad, which has been affected by the high temperatures. This is only the top layer and will disappear over time (gradually, as there isn´t a line to draw of where the lower friction part of the pad is)

The prolongued travel is caused by a increased compressibility of the top layer of the brake pad (again fractions of a millimeter), also caused by the heigh thermal stress on the pad. When this layer had worn off, the longer pedal travel has gone."
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Old 11-23-2006, 10:42 PM   #7
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Quote:
Originally Posted by 1996 328ti View Post
Like I said, I start to get some fade on my 6th day.
Minimum of once a day when on track? Sorry, but that is just overkill unless it is very hot out and you are running solid rotors. Maybe you need brake ducts?
I take care of 6 rental race cars, and a handfull of customer cars. I've tuned/prepped cars that currently hold D/E/F Production track records at Seattle, Portland, and Thunder hill. Yes I have brake ducts....

I always bleed the brakes before a race session. or and important qual. Its worth .02 to .03 of a second per lap with a good driver.

I rented a Flir camera last year so I could check brake temps on the moving cars, was interesting to see who's brakes were working and who's werent.

If your car works and your happy then we are all happy!
Because my car will be in front of yours

Dave
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Old 11-23-2006, 11:08 PM   #8
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Quote:
Originally Posted by pdxmotorhead View Post
If your car works and your happy then we are all happy!
Because my car will be in front of yours
If I had a lift or a garage it would be a different story. I believe the OP was talking about DEs though.

If I was charging someone to bleed their brake fluid, I'd recommend that too.
I'd be changing their oil also.
I'm not looking for improvements in .01s. I'm happy if I can be 00:01.0 faster each time. My goal is to drive my car home, not be a HPDE champion.
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Old 11-25-2006, 03:01 AM   #9
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I don't use a lift, I'm working on these cars at the track...
Jack stands, wheels off pump them out.

Believe me there aint much profit in renting race cars. We mostly do it to get people into racing.

All of our cars get brand new redline after each school or race weekend.... We then recycle it into the tow rig...

Schools are WAY tougher on the cars than race weekends.
School track time can add up to about 3 hours a day, where race weekends its 1.5 hours... For the whole weekend! Plus the newby drivers beating the crud out of the clutch and brakes and tires....

Have fun!

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Old 11-25-2006, 08:05 PM   #10
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3 hours a day? I wish. I've only been able to get 3 hours a weekend and that is only if the sprint and enduro races complete on time. What DE's give 3 hours a day?

My last DE the event organizer put his 911 into a wall and that took 35 minutes to get cleared up. So they pushed each run group out and the last run group, novice, only got 10 minutes instead of 30. I can't wait until I'm running in the advanced or Solo groups as they get their runs in early and seem to get the full time each time.
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Old 11-25-2006, 10:42 PM   #11
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Quote:
Originally Posted by mohaughn View Post
My last DE the event organizer put his 911 into a wall and that took 35 minutes to get cleared up. So they pushed each run group out and the last run group, novice, only got 10 minutes instead of 30. I can't wait until I'm running in the advanced or Solo groups as they get their runs in early and seem to get the full time each time.
It depends. Some schools put the novices up first so they can finish early figuring and probably so instructors can head home. A group is normally last to leave. The nice thing about A is I don't have to lift when giving a pointby since almost everyone has more hp.
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Old 11-26-2006, 04:41 AM   #12
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Wow. My club runs a few a year in Portland, the way it works for us is we run 3 run groups, 1,2,3 we start with 30 minute sessions, if something happens we don't change the schedule, the group causing the problem eats the clean up time. Of course we also have a tow truck and make it clear to the drivers, if they punch the wall, the car belongs to the tow company till its back in the pits and clearing the mess over-rides damage to the car. We try to avoid any secondary damage, but everybody paid to play and they shoudn't lose time over 1 yoyo's mistake.

So in a 9 hour day each rungroup gets 3 hours on track, we take an hour for lunch, so its 10 hours total.

BTW its
Group 1 = Novice w/instructors (Only allow passing on front straight)
Group 2 = Experienced Instructors optional (Passing rule is front and back straight only.)
Group 3 = Prepped cars / exotics / very experianced. ( passing is point by, + above)


Cheers!
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Old 11-26-2006, 05:06 AM   #13
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Ahh.. So it is just a DE, no racing. PBOC does their DE along with their sanctioned races. So there is the novice group, intermediate/advanced, solo, and the race groups.

Usually on Saturday the race group gets 1 practice and 2 30 minute sprint races. And on Sunday they get 1 practice session, 1 60 minute enduro, and a 30 minute sprint. All of the DE groups get 3 30 minute sessions each day. I've heard that they are normally pretty good about keeping on schedule but this one particular incident happened in the race group, and it was a point race and they were not going to cut the race short as it was a point race. Passing is also only on a point by basis, but there are five or six different passing zones.

So the last group of the day, novice got combined with solo and the session was cut short..
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Old 11-26-2006, 05:17 AM   #14
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I'm as guilty as the two of you for going off topic, so let this be the last one.
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Old 11-26-2006, 11:25 AM   #15
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Quote:
Originally Posted by 1996 328ti View Post
I'm as guilty as the two of you for going off topic, so let this be the last one.
I think going off topic does not matter. Interesting to see what a topic can trigger of related issues

But I am suprised if none of you guys have experienced prolongued brake pedal (due to increased compressibility of the top layer of the pad) at track days. It is quite common on BMWs in my club.

PS! I do alwas start a track season with new pads, fresh fluid (Castrol SRF or ATE Typ 200) and bleed my brakes (the old way) at the end of each track day.
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