Brake rotors can't be turned on a 964?????

Bill Wagner · 08-13-2001, 08:43 AM

I took my car to a local p-car shop today, primarilly to get new tires put on. This shop does not have a good reputation, but I figured they could handle some simple tasks (tires, balancing, and checking out the squeal from my brakes).

As far as the squeal from my brakes went, I took in a TSB about it and brake dampers. I was assuming the work would include new dampers, and maybe turning the rotor and putting on new pads. Like I said, this place does NOT have a good reputation. In any case, I got a call from the tech and he's claiming my brake pads have dried out and glazed the rotors. I told OK, then turn the rotors. His response was he couldn't turn the rotors because Porsche doesn't recommend it. He's also (surprise, surprise) recommending what amounts to a complete overhaul of the rear brakes...new rotors, new pads, new dampers, etc. etc.

My question for the day: Is turning rotors not recommended. If not, then why does my 964 spec book provide information about the limits of turning the rotors? (I suspect I know the answer to this question, I just want verification).

Thanks in Advance,

Bill Wagner

JohnC · 08-13-2001, 09:13 AM

Generally speaking, rotors don't need to be turned at all. Except when they become warped.Otherwise if the rotor becomes glazed break the glaze with sand paper or maybe scotch brite.

Mike Feinstein · Mike Feinstein's Garage

Bill,

I'm probably asking the obvious but. . .if you knew that this shop had a bad reputation???....do I need to finish the question?

Check your manual and get the thickness spec for the rotors. Have this guy measure the rotor thickness (or better, go there and do it yourself) with calipers. If they exceed the spec in the manual, instruct him to turn them (or leave them alone and replace the pads). . .remember, you are the customer.

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Mike
94 C2 cab

[This message has been edited by Mike Feinstein (edited 08-13-2001).]

Bill Wagner · 08-13-2001, 12:10 PM

Mike:

There are some tasks (putting on tires, balancing, and brake maintenance) that I would assume even the most incompetent of shops should be able to do without being challenged.

Apparently I'm being proven wrong yet again.

Bill Wagner

964Cab · 964Cab's Garage

Two months ago I bought a '90C4 Cab and in it's records was a rotor/turned repair bill for all 4 vented disks done by a local generic gas station ! A rotor is a rotor.

PS: I don't have drilled disks, I think that came on the 993 ?

gfogal · 09-05-2001, 03:23 PM

Hope this isn't too late for ya Bill, but I just had my 911SC rotors turned because they were scored (the mechanic made sure they would stay within spec before he would even accept them for turning). If your rotors are scored, grooved, or glazed (and you don't race), then I would recommend turning them. I wouldn't turn them to remove a warp, because the decreased heat retention will cause the warp to reappear eventually.

Britwrench · 09-05-2001, 09:39 PM

A couple of points on this;
If the rotors are not scored, worn or in any way damaged I wouldn't turn them. Thoroughly clean them and the calipers, grease the ends of the pads and refit everything.

For shops, there is the problem of customer come-back. If new discs are fitted then any possiblity of doing the job again is minimised. If they need to be turned I would always have them surface ground.

Superman · 09-05-2001, 11:24 PM

Yes, it sounds like you know the answer to your question. I have replaced a number of brake pads in my day (perhaps the same number that John Walker does in a week, but I'm still proud of my experience) and I like just using scotch brite. I've replaced pads without doing anything to the glazed rotors and this gets you poor brakes.

If there are lots of 'bump' grooves, then the new pads won't seat as quickly as if you turned the rotors. but I feel I've had good results with scotchbrite pads. Get one of those approx 2-inch holding fixtures for the 2" scotchbrite pads that mounts onto a drill. Hardware stores probably have them. Then use the drill and pads to scratch the heck out of the rotors. They're pretty hard so it's not easy to hurt them, but it's also not easy to break that glaze unless you use a power tool. Again, this method has worked well for me, but the pads probably take a couple hundred miles to fully seat. I have experienced no brake problems during this period because the glaze-breaking treatment seems to get good brakes with new pads.

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'83 SC