C376FL

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

Procrastination Racing

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.

Bikergems

Rotor runout is the thickness of the rotor.
One answer to your question is "all the above."
What is your problem with your brakes?

C376FL

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

68Thunder427

Sounds more like you have a bad master cylinder and / or brake booster. Are you noticing pulsating or vibrating from the rotors when stopping?

Tooonz

My rotors are separated, and I did not mark the orientation. So now what do I do? How does one shim them?

C376FL

Hi 68thunder427! I have not noticed any of the above problems you mentioned. I'm not sure what is the best to start with. Like I said there is a problem with finances wright now. I have been checking just the different things it could be.
Thanks for the help.
Larry

pws69

Not true at all.

Rotor Runout is a measurement of how much the rotor "wobbles" at the pad surface due to uneven inner mating surfaces (rotor to shaft flange). Rotor Thickness has nothing to do with it.

Mick71

http://forums.corvetteforum.com/c3-t...tor-shims.html

C376FL

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

redvetracr

that is incorrect!!

http://www.kwik-way.com/techdoc/blog1.php/rotor-runout

my 76 ray

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.

C376FL

I have another brake question, as I stated above about rebuilding the master cylinder, I checked the brand I have, and I can not find a name. But the casting number is correct for a 76 AcDelco with power brakes. Do I need AcDelco rebuild kit, or will any brand work? I have checked local parts stores and they do not have the kits in AcDelco. If other brands work what ones would you recommend?
thanks
Larry

Bikergems

I stand corrected!

Peterbuilt

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.

CaseyJones

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.