Brake information
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Joined: Oct 2007
Posts: 87
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From: Davenport Iowa
Brake information
Is brake run out the distance between the brake pad and the rotor? How do you adjust this? How can I tell if my calipers are O.E. if so can I rebuild them to o-ring seals? How hard should my brake peddle be with the car off? If the peddle is soft and won't firm up after 3 or 4 pumps does that mean the booster is bad? I've owned my 75 for 4years and have had the brakes bled at least once per year they stay firm for a week or 2 then right back to no peddle. The brakes always stop the car and will lock up all the wheels. Spent all weekend bleeding the brakes with speed bleeders went though 2 quart of fluid still no peddle.Can't afford to just throw money at the problem and would like to fix it my self for the satisfaction of doing it I have more time than money.
Race Director
Joined: Jul 2001
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Rotor runout is a lateral 'wobble' of the friction surface as it rotates. This means it gets closer to and further away from a stationary object- like the brake pad. This changing clearance causes the brake pedal to shudder and in extreme cases cause air to be drawn inside the calipers giving a low pedal.
Sounds like that's your problem.
Start by measuring the actual runout with a dial indicator. If much over .005", plan on having the rotors machined in situ or shimming them from behind.
Sounds like that's your problem.
Start by measuring the actual runout with a dial indicator. If much over .005", plan on having the rotors machined in situ or shimming them from behind.
Drifting
Joined: Jul 2007
Posts: 1,889
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From: Kansas
There was a recent article on this, on this forum. I would think shimming them from behind would be the easiest, I can't image taking my axles out to machine them on a street car. I guess it would be up to you. Of course the last time I pulled the axle out, I had to install new bearings & it took me about three times to get the shim right on it. I wondered if the seal would be any good, having it out so many times. LOL Gene
Thread Starter
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Joined: Oct 2007
Posts: 87
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From: Davenport Iowa
So if I replace my calipers with the new o-ring type will this take care of the run out issue.Also how hard is it to change rotors and do I any need special tools. Is there some way to test my booster it is O.E.
Burning Brakes
Joined: Jan 2006
Posts: 1,152
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From: Kawartha Lakes and PEC, Ontario
Changing to o-rings is a workaround. With o-rings the piston fits so tightly in the bore that the springs behind the piston no longer cause the pads to ride on the rotor pulsing in and out with every turn of the wheel. (if there is no run-out...there's no pulsing, no issue)
You should be able to get a dial indicator to measure the runout for a reasonable cost. ~$20 with a magnetic base. That's really the best way to find out for sure if runout is the problem. If it is you can:
1. have the rotors machined while on the car
2. shim the rotors from behind
3. index the rotors (pull them off, turn them one hole, reinstall and measure runout again, repeat until you hopefully find a configuration with an acceptable amount of runout)
4. change to o-ring calipers
I think #1 is probably the best solution. I did 3 and 4 together 3 years ago and haven't had any trouble since.
