I have a 76 and the brakes are driving me nuts. I have searched this and other forums and have come to the conclusion that I am having rotor run out problems. The car was my uncles and when he heard I was looking at vettes he sold it to me for a pretty good price. He had not driven the car for 2 years and it had been sitting in his garage. I have talked to him about my problems, and he is surprised, as he had the brakes done the day before he put it away two years ago. New rotors, pads and SS sleaved calipers all around. After getting the car I drove it about 300 miles with a steadily worsening (mushy) brake pedal. Replaced the master cylinder, bled the brakes and had great brakes, for about 500 miles.Then the same thing again.

Took the car to the local vette shop and was told that some one had sprayed some kind of adhesive on the pads to try and stop squealing brakes and that one of the rear rotors was miss indexed. They told me they would be happy to fix it for me, for just under $1200.00 :eek:

Needless to say the car sits in my gerage. I have pulled the rears and am taking the rotors in to be turned tomorrow. Rather than deal with cleaning up the pads (less than a 1000 miles on them) I am replacing them. I am also installing the o ring kit that I have read about here.

My questions are:

1. What else should I be doing at this point to fix this problem?

2. When I pulled the rotors I noticed that indeed they were indexed differently. On one the two larger holes in the rotor were lined up with the corresponding holes in the hub. on the other they were not. Is this a possible source of problems, and if so what way should it be? Seems to me it shouldn't matter, but does it?

Thank you for your help. 20 years in the service didn't make me a mechanic, but it sure took away my fear of tearing into things......

 

I am interested in hearing what everyone thinks about this as well. Here's a TTT for ya! :seeya

 

consider getting o-ring pistons. They will tolerate more rotor runout without pumping air into your lines and causing the mushy pedal.

 

The solution is the o-ring kit. I went through this. For less than $50, and about an hour of your time, your problem will go away.

Other than that, if your fluid is dirty, flush it out.

That's it.

 

the solution is to fix the runout! did you measure the runout before you removed them? if the rotors were brand new and made in north america when they were installed 2 yrs ago, chances are they are probably running very true. most of the time the spindle will be the source of the runout. there is no point in remachining the rotors if there are good. have the shop verify the runout on the lathe beforehand. then bring them home and shim them on the spindle. it is pretty easy to get them to run within .002".

 

the rear rotors have extra holes for tool clearance to adjust the parking brake. someone probably tried to compensate for the perceived runout by mounting the rotor off of it's regular orientation. but this will not solve the problem at all because the spindle is suspect.

 

:skep: :skep:

There are only 5 "correct" holes on each rotor hat. Perhaps someone was trying to fit the drilled out rivet holes onto the lugs, or (already mentioned) use the hole for the parking brake adjustment - but there aren't enough of those (only one as I remember). Make sure the correct holes are being used. I would have thought there would be some wear indicating the correct holes.

As you brake to a gentle stop, is there any pulsing in the brake pedal? Pulsing is typical of rotor wobble (runout). I've also seen dark areas on the rotors with alternate bright areas on the rotor which also might indicate out-of-spec runout. Causes might be the rotor itself or bad bearings.

Good luck... :)

 

Thought I should let you all know what I found out at the machine shop today. Runout on the left rear was found to be .008 and on the right rear .005! This on rotors that although 2 years old have less than a 1000 miles (mostly highway and all easy) on them.

The shop told me that they highly reccommend turning all rotors before installation. They sell all types in their parts store, foreign and domestic, and they claim that even the "good" American stuff very commonly comes in "warped".

I am now waiting for my caliper "O" ring rebuild kit to get here. I think I am gonna go ahead and pull the front rotors and have them checked and turned if needed.

Thanks for your input guys

 

Here ya go:
http://forums.corvetteforum.com/zerothread?id=810889