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Author Topic: Brake question
Phil Mather Verified Driver Made Donation to Website
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Region: Detroit
Car #: 06
Year : 1990
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When my brake pads are almost gone, I get a very long brake pedal. I have learned to deal with this by giving the brakes a quick pump on the straight to push them back into place. When the car cools and sits for a while, the first time I hit the brake pedal it goes to the floor and needs to be pumped up.

Is this normal? Its an un-nerving feeling.

Thanks!

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Phil

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Mark de Regt Verified Driver Made Donation to Website
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Region: NWR/Oregon; ICSCC
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Year : 1991
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Exactly the same thing happened to me at my last race. I planned to change the front pads at the end of the day; there was enough material to get me through qualifying. On the first hard braking point, the pedal went right to the floor, and I kept going. Quick pumping got me stopped before any damage was done, but it was interesting. The rest of the session went with a good firm pedal, and I changed pads right after.

Examining the pads showed that the pads had developed a bit of a wedge shape; I suspect the general "long pedal" is from having to push a bit more each time because the pads are more likely to pull back from the rotor; I'm not sure why I lost it all once.

Tom's Double O Verified Driver
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Region: Oregon
Car #: 00
Year : 1992
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Phil,

A few more details are needed;

What type/brand of fluid are you using?

Have you tried bleeding the brakes and leaving the old pads on? If so, did that temporarily solve your problem? I say temporarily because if it is what I think, the problem will quickly return.

Typically, when the pads are almost completely gone it leaves very little brake material to insulate the caliper and brake fluid from the high rotor heat. This can in turn boil your fluid and leave you with a soft/no pedal. Problem is typically resolved when changing pads, because I'm sure most of us will bleed the brakes at the same time we change pads. Problem doesn't return until the pads wear out again.

Tom

Phil Mather Verified Driver Made Donation to Website
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Region: Detroit
Car #: 06
Year : 1990
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I'm using Wilwood 570 Racing Brake fluid. I have bled the brakes many times with and without changing pads and there have been no air bubbles and the brake fluid is still clear.

The last time this happened at the track, I jumped into the car to go out for the afternoon qualifying after the car had been sitting in the pits for a few hours. The brake pedal went straight to the floor. It pumped back up fine, but the pads had retracted after everything had cooled. Pads were fresh that morning and brakes had been bled.

--------------------
Phil

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CarbotechDanny Made Donation to Website
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Guys,

This has nothing to do with the brake pads. When the pedal goes to the floor all of a sudden and you have to pump it up to get the pedal back it is fluid related, unless you are getting pad knock back.

Pad knock back usually happens after you go over some rough FIA curbing and you knock the pad loose and at an angle. When you get pad knock back you only have to pump the pedal once (usually).

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Danny Puskar (push-car)
Carbotech Performance Brakes
4031 Dearborn Place N.W.
Concord, NC 28027
877-899-5024
danny@ctbrakes.com
http://www.ctbrakes.com

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CarbotechDanny Made Donation to Website
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quote:
Originally posted by Mark de Regt:
Examining the pads showed that the pads had developed a bit of a wedge shape;

That's because the pad(s) got hung up in the caliper at some point and were at an angle.

When they went away all of a sudden that could have been pad knock back. This is also why I recommend using those spring clips, they help eliminate pad knock back.

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Danny Puskar (push-car)
Carbotech Performance Brakes
4031 Dearborn Place N.W.
Concord, NC 28027
877-899-5024
danny@ctbrakes.com
http://www.ctbrakes.com

Puskar Motorsports
Spec Miata specialists
Chesterland, OH
216-406-8140

Phil Mather Verified Driver Made Donation to Website
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Region: Detroit
Car #: 06
Year : 1990
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Thanks Danny. But let me repeat, this is not happening on the racetrack (except for pad knockback, I am familiar with that). My pedal goes to the floor after the car has cooled off. That is what I am wondering about. On track, the brakes are great (Carbotechs, btw) [Smile] Once I pump the brakes up in the paddock and get on track, they are fine. No need to pump them up.

--------------------
Phil

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CarbotechDanny Made Donation to Website
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Ask Mark Bennett, he is a brake engineer and should have the answer. I would look at the brake booster and/or master cylinder. Bennett will point you in the right direction.

That is weird...

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Danny Puskar (push-car)
Carbotech Performance Brakes
4031 Dearborn Place N.W.
Concord, NC 28027
877-899-5024
danny@ctbrakes.com
http://www.ctbrakes.com

Puskar Motorsports
Spec Miata specialists
Chesterland, OH
216-406-8140

jnjj Verified Driver Series Champ
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Region: Houston
Car #: Wheels Am SM Champion 2004 & 2005
Year : #43-- 1999 & # 1-- 1990
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Sounds like a master cylinder is starting to fail,booster only helps supply the foot pressure so your legs dont have to strain to hard to apply pressure

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JP3
Team PhillipsRacePrep

Phil Mather Verified Driver Made Donation to Website
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Region: Detroit
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Year : 1990
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Now that you mention it, I think i forgot to put a checkvalve in when i added the supercharger so there is now positive pressure on the wrong side of the boost....err...i think i've said too much... [thumbsup] [laughing]

Thanks for the help guys!

--------------------
Phil

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Jay Lutz
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Region: Indy
Car #: 33
Year : 1994
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And I'm an ex brake engineer as well....worked for Bendix, Kelsey Hayes, Ford. Call if you need any help. Jay

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"In our sport if you go out of bounds you're most likely not coming back" Michael Waltrip

nohairracing Verified Driver
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Region: neohio
Car #: #50
Year : 91
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Phil
Have you checked the master cylinder pushrod length?
Howard

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Never argue with an idiot, they drag you down to their level then beat you with experience!

TexasHammer
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Region: LoneStar
Car #: 02
Year : 1991
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I've had this problem too. I was running the Hawk HP+ and at MSRH the pedal was goin to the floor and did not inspire much confidence. Upon switching to Hawk Blues the problem disappeared and I have been happy since. That was 2 weekends ago. BTW, I did not bleed after changing. The old pads were worn down to about 1/16". I figured that I am harder on the brakes than the pads could handle. I also like the idea of adding a check valve. Shouldn't be necessary as the master is above the caliper, but maybe as the pads wear, the master, upon returning to idle position, will actually suck the fluid out of the caliper, instead of the reservoir. HMMMM

Keith in WA Verified Driver Made Donation to Website
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If it's the pushrod, wouldn't it be a constant problem vs. pump up the brakes and it goes away?

I have a similar problem and think there is air stuck in my master cylinder which can be difficult or impossible to bleed at the wheels.

   

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