[getmygoat]

Hi all,

I've been chasing a vibration on my 1970 GTO. I noticed recently a rotor is warped (tight spot when rotating the rotor by hand. ) - This is logical as immediately after the restoration I had a caliper seize up and that brake was smoking pretty good. I replaced the caliper but left the rotor alone.

So - now the big questions :

1) Can I turn a rotor to eliminate warpage due to overheating, or should I just replace it? ($60 for a new rotor)

2) Could a warped rotor cause a vibration at 60-80 MPH without brakes applied? (I do get a slight vibration when I apply the brakes semi-strongly at 20MPH.

Thanks!
Fred

[Jeff Walker]

If you have a warped rotor you should feel the pedal pulsate when you step on the brakes. Do you? HTH

[getmygoat]

Originally Posted by Jeff Walker

If you have a warped rotor you should feel the pedal pulsate when you step on the brakes. Do you? HTH

I haven't noticed it, so it might be there, but not bad enough to get my attention.

but like I said, there's a tight spot when turning the rotor by hand... so that's gotta mean something, no? also, I definitely have a vibration with moderate application of brakes.

the more interesting question (for me at least) is whether this could cause a vibration at speed w/o brake application.

[engineer]

check runout with dial caliper. not too bad, can be turned if no apparent heat spots. A lot, get a new one. could also be caliper bent from heat.

[sleepy]

Take the pads out an turn the rotor. you might find a bad bearing.

[bluebandit]

Im guessing yes it could. If it has a tight spot it could be heating the rotor up and causing it to warp some more. I worked on a car once that had a bad brake hose that kept pressure on the caliper. As you drove it the rotor would get hot and the whole front end would start to shake. If you could get to sixty quickly before the brakes get to temperature does it do it or after a little while at speed. Myself I would just replace the rotor.

[getmygoat]

thanks all.

The caliper was replaced a while back. The brakes generally work fine now (the freezing caliper is replaced/fixed). The brake hoses and wheel bearings are new.

Interestingly, I took it to a well known pontiac mechanic in San Diego, and he suggested new wheel bearings but he never noticed the warped rotor.

I'll check the runout - but I'm tempted to just replace the rotor... I really want to get to the bottom of this vibration issue.

[x-bird2]

yes, warped rotors can cause discernible vibrations. rotor diameter and how badly warped determines just how discernible it can be. my dad recently got a used lexus with just the ever-so-slight vibration that could be felt really only through the steering wheel around 35-50 mph--and barely so. after a few days of hunting around on it, found the driver's side rotor to be slightly warped--wasn't noticeable during braking, just acceleration.

[getmygoat]

Well, this morning I swapped out the passenger side rotor for a new one.

It seems like the vibration at speed might be slightly better, but there's still something there.

However, now I've created a new problem, which is that the car pulls to the drivers side under moderate braking. (So the new rotor doesn't seem to be grabbing like the old one). Also, I still have vibration when hitting the brakes.

Was I stupid to just replace one side? I did compress the caliper to get the pads back on, but after several pumps the pedal firmed up, but now it doesn't seem to grab hard enough.

What do you think?

[bluebandit]

When your caliper locked up originally did you replace the pads also. Wondering if the pad glazed over on that side.

[sleepy]

Could be a number of things. Did you spray down and clean the new one with Brake-klean? the other side might be glazed. And brake pads need some time to wear in. That's why it's a good idea to replace both sides at the same time.IMO

[getmygoat]

Yes, I cleaned the rotor with brake parts cleaner before mounting it, (and I kept in clean).

I never replaced the pads, but if the prior overheating had screwed up the pads, it seems that would have showed with the old rotor as well?

Maybe I should replace the pads on both sides and the remaining (old) rotor?

[sleepy]

O I thought you replaced the pads with the roter. I would replace the othe one or have it turned. In this case the cost of replacing both rotors and pads shouldn't be that much. Plus if you replace it all it will narrow down the posibilities for the vibration.

[getmygoat]

I replaced the pads with semi-metallic and both rotors. Now the car stops evenly and the vibration is pretty much gone! Thanks all!

[mike_dmt]

Thats great. Brakes can do that sometimes. I seem to warp rotors FAST on everything Ive ever owned. Lead foot=Lead brake foot! Regardless, I always replace pads in pairs if not sets. Even if I just had the rotors turned because, you may have glazed the pads. Now, one thng I would always recommend is to properly seat the pads to the rotors. Every (decent) brake pad manufacturer worth its salt should have some instructions on its site to help you with this. I just put some Brembo rotors on my BMW, and they had some different recommendations on bed-in procedure depending on the type of pads. Sure enough, that thing stops hard enough to pop your eyes out. As far as your vibration at speed, a reputable tire/wheel sop should be able to sort that out. Sounds like a balance problem to me.

[PITTSBURGH 64]

You will want to adjust the rear brakes by hand or the new set up will warp again. You want the rear brake drum so its hard to get back on. Self-adjusters rarely work right...

[bluebandit]

Glad to hear you are getting your ride sorted out. That last little bit of vibration could be a tire slightly out of round. Also if they have been balanced you might want to try a different shop. Ran into that one awhile back. Two balance jobs, both times with the same results, shaking. Took it to one of their other shops and got them balanced out first go round. Turned out the first balancer was having some problems. Good luck.