Brake question
Thread Starter
Racer
Joined: Jan 2014
Posts: 407
Likes: 14
From: Mulberry Florida
Brake question
Hi all! When you refer to rotor runout, and there is a problem is it usually a warped rotor, bad wheel bearing, or is it something else. I have read here that if runout is off it causes the pistons to flutter and the lip seals to let air in to the system. I have problem with my brakes, and I have not checked to see if my calipers if they are lip seal or o-rings yet.
Thanks for the help
Larry
Thanks for the help
Larry
Le Mans Master
Joined: Feb 2001
Posts: 6,304
Likes: 278
From: Ocala FL
It is caused by a cheap manufacturing process. To save money, the stub axles on the rear were not machined to perfectly square faces. Same on the inside of the rotor hubs. After all, once they were riveted together as a unit, the rotor could be machined square to the axis of the axle, and that is all that counted.
All is good until you:
1. separate the rotor and don't put it back in the same spot
2. separate the rotor and have it turned independent of the axle
3. replace the rotor with another
Then you need to shim the rotor to reduce run-out.
Most C2 C3 rotors don't warp. They are very thick and heavy. It takes really serious heat to warp them.
Bad bearings can let them wobble.
All is good until you:
1. separate the rotor and don't put it back in the same spot
2. separate the rotor and have it turned independent of the axle
3. replace the rotor with another
Then you need to shim the rotor to reduce run-out.
Most C2 C3 rotors don't warp. They are very thick and heavy. It takes really serious heat to warp them.
Bad bearings can let them wobble.
Last edited by Procrastination Racing; Jul 9, 2014 at 09:57 PM.
Thread Starter
Racer
Joined: Jan 2014
Posts: 407
Likes: 14
From: Mulberry Florida
The problem is I have had the car for two years and was driving it on a regular bases. One day I was driving and noticed the brake pedal going down father. When I got home I checked the fluid level, and it was fine. Checked the brake booster by pumping the pedal and holding it, then started the engine, the pedal went down. I have not seen fluid anywhere on tires or master cylinder. So I assume there is air getting in the system. I have not been able to do much yet because of some unforeseen expenses. I do not want the car sitting on jack stands for a long period of time, until I'm able to spend the money.
I thank you all for the help.
Larry
Pro
Joined: Feb 2014
Posts: 692
Likes: 2
From: Seguin TX
Bikergems
The problem is I have had the car for two years and was driving it on a regular bases. One day I was driving and noticed the brake pedal going down father. When I got home I checked the fluid level, and it was fine. Checked the brake booster by pumping the pedal and holding it, then started the engine, the pedal went down. I have not seen fluid anywhere on tires or master cylinder. So I assume there is air getting in the system. I have not been able to do much yet because of some unforeseen expenses. I do not want the car sitting on jack stands for a long period of time, until I'm able to spend the money.
I thank you all for the help.
Larry
The problem is I have had the car for two years and was driving it on a regular bases. One day I was driving and noticed the brake pedal going down father. When I got home I checked the fluid level, and it was fine. Checked the brake booster by pumping the pedal and holding it, then started the engine, the pedal went down. I have not seen fluid anywhere on tires or master cylinder. So I assume there is air getting in the system. I have not been able to do much yet because of some unforeseen expenses. I do not want the car sitting on jack stands for a long period of time, until I'm able to spend the money.
I thank you all for the help.
Larry
Burning Brakes
Joined: Oct 2013
Posts: 992
Likes: 28
From: Sutton MA
It is caused by a cheap manufacturing process. To save money, the stub axles on the rear were not machined to perfectly square faces. Same on the inside of the rotor hubs. After all, once they were riveted together as a unit, the rotor could be machined square to the axis of the axle, and that is all that counted.
All is good until you:
1. separate the rotor and don't put it back in the same spot
2. separate the rotor and have it turned independent of the axle
3. replace the rotor with another
Then you need to shim the rotor to reduce run-out.
Most C2 C3 rotors don't warp. They are very thick and heavy. It takes really serious heat to warp them.
Bad bearings can let them wobble.
All is good until you:
1. separate the rotor and don't put it back in the same spot
2. separate the rotor and have it turned independent of the axle
3. replace the rotor with another
Then you need to shim the rotor to reduce run-out.
Most C2 C3 rotors don't warp. They are very thick and heavy. It takes really serious heat to warp them.
Bad bearings can let them wobble.
Last edited by Tooonz; Jul 10, 2014 at 09:19 AM.
Thread Starter
Racer
Joined: Jan 2014
Posts: 407
Likes: 14
From: Mulberry Florida
Thanks for the help.
Larry
Melting Slicks
Joined: Nov 2001
Posts: 2,668
Likes: 43
From: Eastern US XX
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Melting Slicks
Joined: Nov 2010
Posts: 3,363
Likes: 32
From: Bowtie, Pennsyltucky
St. Jude Donor '13-'14-'15,'21
Thread Starter
Racer
Joined: Jan 2014
Posts: 407
Likes: 14
From: Mulberry Florida
Thanks all!
I think I will start with pulling the master cylinder and rebuilding it first, it looks to be the cheapest to do. I rebuilt a master cylinder years ago I hope I can get it done wright this time. I looked on the forum for a how to, but was unable to find one. Plus I have read be sure to bench bleed before install. I have not read a post on how to do it. That might sound stupid, because it could be such a simple thing to do. I'm not the brightest
in my old age.
I thank all of you for the help.
Larry
I think I will start with pulling the master cylinder and rebuilding it first, it looks to be the cheapest to do. I rebuilt a master cylinder years ago I hope I can get it done wright this time. I looked on the forum for a how to, but was unable to find one. Plus I have read be sure to bench bleed before install. I have not read a post on how to do it. That might sound stupid, because it could be such a simple thing to do. I'm not the brightest
in my old age.
I thank all of you for the help.
Larry
Race Director
Joined: Aug 1999
Posts: 18,126
Likes: 174
From: WI
Melting Slicks
Joined: Mar 2007
Posts: 2,520
Likes: 11
From: Hinckley OH
If you are reusing the original rotors and they have not been turned then you should be able to find the correct orientation by trying each of the 5 different orientations and measuring the runout.
Thread Starter
Racer
Joined: Jan 2014
Posts: 407
Likes: 14
From: Mulberry Florida
Thanks all!
I think I will start with pulling the master cylinder and rebuilding it first, it looks to be the cheapest to do. I rebuilt a master cylinder years ago I hope I can get it done wright this time. I looked on the forum for a how to, but was unable to find one. Plus I have read be sure to bench bleed before install. I have not read a post on how to do it. That might sound stupid, because it could be such a simple thing to do. I'm not the brightest
in my old age.
I thank all of you for the help.
Larry
I think I will start with pulling the master cylinder and rebuilding it first, it looks to be the cheapest to do. I rebuilt a master cylinder years ago I hope I can get it done wright this time. I looked on the forum for a how to, but was unable to find one. Plus I have read be sure to bench bleed before install. I have not read a post on how to do it. That might sound stupid, because it could be such a simple thing to do. I'm not the brightest
in my old age.
I thank all of you for the help.
Larry
thanks
Larry
Le Mans Master
Joined: Aug 2006
Posts: 7,417
Likes: 1,554
From: mount holly NC
2025 c3 ('74-'82) of the Year Finalist - Unmodified
2019 C3 of Year Finalist (appearance mods)
On a budget?
Have you bleed the brake system yet?
One bleeder on each front wheel and an inner and outer bleeder on the rear.
If you get a lot of air make note of which wheel.
If you have rotor runout the brakes will fail again.
If you do get to replacing the M/C here's how to bleed it.
One bleeder on each front wheel and an inner and outer bleeder on the rear.
If you get a lot of air make note of which wheel.
If you have rotor runout the brakes will fail again.
If you do get to replacing the M/C here's how to bleed it.
Melting Slicks
Joined: Jul 2010
Posts: 2,503
Likes: 33
From: McGrady NC
St. Jude Donor '15-'16
The rear rotor specifically should line back up if you watch for the hole in the rotor hat area between the holes for the wheel studs used to reach through to adjust the parking brakes. that is if you didn't switch the rotors side for side.