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first gen brake pedal is soft

Old 07-27-04, 10:22 AM
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first gen brake pedal is soft

the pedal in my race car is soft, and i dont know why. i can still lock up the wheels but it takes the pedal being almost to the floor to do this. at this point i cant tap the gas to downshift, my foot is too low. it didnt used to go down so far, im not quite sure what the problem is now.

i have bled the brakes many times, there is NO air in the lines. unless there is a trick to get air out of the m/c that im not aware of, its been bled very well.

the m/c doesnt seem to be going bad. i know the usual symptom here is to have the pedal fall to the floor after you hold it down. this does not happen. im not sure if the m/c can fail another way or not, ive never actually taken one apart.

all the calipers seem to be ok, none are leaking anyway. the car has SS lines and hawk blues all around. anyone have a suggestion before i just start replacing parts?
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Old 07-27-04, 10:49 AM
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Was the MC bled before it was installed? Also when did this start? More info?
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Old 07-27-04, 12:25 PM
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the MC on the car has been on there forever. i havent changed it since the problem started. im not sure exactly when this started happening, its just been getting a little worse with each race. i did a little searching around and found the rear discs wont adjust by themselves and you have to use the e-brake (which i dont have) to adjust them. im going to try to adjust them by hand tonight and see if that fixes the problem...
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Old 07-27-04, 01:00 PM
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That is a problem, removing the parking brake but leaving the hardware for the parking brake inside the rear calipers.

When is the last time you rebuilt your calipers?

I drove a friends Pro7 car that gutted the parking brake hardware from the rear calipers, WOW!!!!! The car will actually squats under hard braking, instead of nose diving.

I tapped the hole in the back of the caliper and installed a Stainless steel bolt once I removed the ratchet hardware.

Now you will need to install a 2lb pressure residual valve (2lb) keep fluid pressure at the rear calipers. Some racing class won't allow this valve, but its easy to hide. Not that I would ever break the rules.


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Old 07-27-04, 01:20 PM
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the rear calipers have not been rebuilt since ive owned the car, but i do plan on rebuilding the entire system this winter.

i dont have a problem getting rear brake out of the car, i can lock up the rear wheels at will if i put the bias to the rear. the car stops like a mother, the problem is when it does i cant reach the gas pedal to downshift so im hosed.

where do you find a 2lb pressure residual valve? im fairly sure it would be legal in IT-7 as removing the parking brake is legal, and technicly thats part of removing the parking brake. either way it offers no performance advantage, its just convient.

now that i think about it when the bias is all the way forward i have a firmer pedal then when its all the way rearward. i cant wait to go home and see if this is the problem...
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Old 07-27-04, 05:57 PM
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You can try cracking(loosen the fitting) a brake line at the MC to bleed the MC...If it isn't air in the line...then you might have a bad MC...Does your car idle poorly, you may have a vacuum leak in the MC? If it does idle poorly, pull the brake booster vacuum line off and plug it...does it idle better???


When was the last time you "flushed" the fluid completely?


how long ago was the last brake work (ie replace pads/calipers/lines?), I know in my Jeep i replaced the front calipers, bled the brakes and went for a test drive...the brakes went almost to the floor...bled them again...and again. The same thing ...After about two days of driving i jumped in my Jeep and the pedal was back at the top and firm?(imagine that) guess the calipers just needed to "seat"....

Just some thoughts...maybe you been through all this already???
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Old 07-27-04, 05:59 PM
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P.S....If you loosen the fitting at the M/C you'll have to rebleed the four wheels...lol
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Old 07-27-04, 08:34 PM
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i might try trying to crack the lines at the MC to bleed it. there is a bleed fitting on the mc, does it do a good job of getting air out?

my brake booster is not hooked up.

the calipers are pretty old, nothing is leaking or anything, i ran about a quart of fluid through the entire system on saturday before my last race. same thing.

i did try adjusting my rear calipers, no luck. im building a pressure bleeder, im gonna try it tomorrow...
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Old 07-27-04, 09:06 PM
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Ok couple of things.
Bleeding brakes, Rt rear, left rear, rt front and then left front.

2nd if your MC is good, then you could have air, or a brake hose that is swelling under pressure..

Power bleeding not necessary, 2 man system works fine.

Brakes are VERY important part of going fast, I would rebuild my front calipers after each race weekend, and rebuild my rear twice a year. Flush prior to race weekend, bleeding prior to each track day.

My .02


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Old 07-28-04, 05:33 PM
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Originally Posted by RussTypeS
i might try trying to crack the lines at the MC to bleed it. there is a bleed fitting on the mc, does it do a good job of getting air out?

my brake booster is not hooked up.

the calipers are pretty old, nothing is leaking or anything, i ran about a quart of fluid through the entire system on saturday before my last race. same thing.

i did try adjusting my rear calipers, no luck. im building a pressure bleeder, im gonna try it tomorrow...
You say your Brake Booster is not "hooked up"??? you are not using the vacumm assissted power system???...If you are using the stock M/C and Booster you will need to connect the vacuum line to the intake manifold...rebuilding the front calipers every race is overkill...you shouldn't have to rebuild your calipers but once a year unless you have problems or have deep pockets
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Old 07-28-04, 06:19 PM
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[QUOTE=RussTypeS]i might try trying to crack the lines at the MC to bleed it. there is a bleed fitting on the mc, does it do a good job of getting air out?
QUOTE]


It should do a good job...some tricks of the trade. while you have the bleeder open on the M/C tap the line and the M/C lightly with a small hammer or large screwdriver handle. (this can help agitate the air bubbles out of the system)
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Old 08-03-04, 01:41 PM
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just to follow up...

i have since rebuilt the front calipers and the car stops so much better. im going to rebuild the rears and the master cylinder before the next race. hopefully that will fix things right up...
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Old 08-03-04, 02:03 PM
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Be sure the caliper slides are free and lightly greased both front and rear; if the caliper sticks on the mount, it will act like you describe (which would explain why rebuilding the front calipers helped a lot). Early (pre'81) front calipers seem to be the worst about doing this. Unless you have an overwhelming reason not to, I'd run vacuum to the booster, having no vacuum can make for really weird pedal feel.
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Old 08-03-04, 03:40 PM
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the only reason i dont run the vacuum to the booster is for pedal feel. its pretty amazing how much more feel you get with the booster disconnected. it does give your leg a workout tho.

i try to keep my slides clean and greased, i ususally check em after every race or two.

on a side note i installed new dust seals on the rebuilt calpers and they have allready just about disengrated from the heat. is it even worthwhile to install these?
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Old 08-03-04, 04:50 PM
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The dust seals also keep water out of the calipers, I'd definitely keep them. But if they are getting crumbly from heat, I'd say that's the rest of your problem. It would be a good idea to build some brake cooling ducts. Make sure you have freeplay in the brake pedal; if there's no freeplay, the brakes will drag all the time and generate massive amounts of heat. Normal is about 3/4 inch, measured at the pedal.
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