Having a hard time finding someone to turn rotors.
 

I have been noticing a hum at a very slow rolling stop. I noticed my rotors have a slight drag that at a point on each side. The aren't warped to a point of causing braking issues. I assume the slight drag is the cause of the humming sound. I brought my rotors to Orielly's to have them turned but they can't get them to fit in their machine with the hubs off. Anyone else find it difficult to get rotors turned?

Chances are slim that you will get an accurate cut without hubs to center the rotors. Then there's the federal limit on how far undersize you can go. Cheap enough to just get new ones. Haven't turned a rotor in years.

+1

I checked the specs and New according to what I saw is 24MM. My rotors are 23.75 and 23.5. Minimum is 22MM from what I saw. I figured I could go to minimum and for no more than I drive the car and the fact that I don't track it, be fine for several years until I'm ready to replace the pads that are basically new. I can get rotors turned for about $15 to $20 per side. The least expensive rotor I saw was $52 for a Bosch.

Turning these rotors is a waste of money, IMO.

You have been given sound advice. You also did the math.
 

First response by JW should have been enough. Just get new rotors if your diagnosis and assumption that the humming sound you hear at low speeds is the cause of your problem. End of story.

Why? Wouldn't buying new rotors when the old ones are only worn by .25 and .5 mm be a waste of money? Again, I don't track my car and don't do a lot of hard braking. It seems to me that spending 30-$40 to have them turned and still being within the legal limits is a better option than spending $104-$130 to gain 2MM.

I get the rotors turned on every vehicle I own unless they are to a point they can't be turned and be within the safe limits. Why should my Porsche be any different when I drive it WAY less than any other vehicle I own? Do all mid 80's Porsche owners just toss rotors? Certainly there has to be someone who has had their rotors turned??

+1 on JW comment. But I would also add the one (anecdotal) and only time I have turned rotors was 20+ years ago on a BMW. Brakes were either ATE or Girling, so similar to Porsche. After getting turned (all within Federal spec), they warped within 500 miles. It was a 320i, so not like I was tracking it or being aggressive on the braking. Never done it since.

There is a reason why no one turns rotors anymore - they are CHEAP. If you have gone through all the trouble to take the damned rotor off in the first place, especially on a 911 where the hub needs to come off, why would you not put a new one on there?

OP, your car do what you want. The national chains will not turn them. Find a local machine shop, it will take awhile but I am sure you will find someone.

In the future, try not to stand on the brakes at stops if level put in neutral and let off he brakes to help prevent warpage.

About 20 years ago I had the front rotors turned on my 75S. Car had classic warped rotor symptom of pulsing break pedal. The pedal and breaks were great for about 4 months then the old symptoms started to return, getting worse as time went on. I then replaced with brand name rotors, and all problems were solved for many, many years. Rob

Scrub them hard with Scotchbrite and put them back on. Lightly sand the pads on a very flat surface, and then bed them in. Flush out the old fluid while you are at it.

Work them. They like that. Porsche Perfection Paralysis. Don't go there.

Oreilly is only about 4 years old in my town. They turn brakes. They just can't turn these because they can't get them in the machine. I'm going to try an old school parts place tomorrow and see where I can get. If they can't get them in the brake lathe, I'll order a new set. Just seems like a waste of steel to get rid of them when they can be turned.

If you absolutely have to do this go to Toyota, or any large dealer really, that has a Hunter cutter that does it while rotors are still on car. Be prepared to do this again after awhile or one or two hard stops. No one cuts them as true as the factory did the first time.

I may be reading this wrong. Hubs off of the rotors or hubs and rotors 1 piece just off the spindle?
You need to turn the rotors while they are bolted to the hub. The machine uses the bearing races in the hub to center itself in the lathe to make a cut perpendicular the bearing races. It is also possible that even a brand new rotor will slightly warp when torquing it to the hub. I've always put a finish cut on new rotors after assembly just to be safe.

Maybe that's the problem? I took these in just like I would any other set of rotors, rotor only. Thanks for the input.

At the shop that I work for, we do not "turn" brake rotors. I work at a Mercedes Benz dealership in Washington, D.C. and the reasons we do not are #1 the manufacturer does not recommended it. #2, typically the metal in brake rotors for European cars is very soft & "turning" the brake rotors to get rid of any grooves or glazing takes way too much material off the surface of the rotor and as a result makes the rotor too thin. The reason the metal is much softer than what you find on a Japanese or domestic car is that when the steel rotor heats, the metal becomes very grippy with the brake pad and as a result, reduces the stopping distance. It's like that on purpose and you can go to any independent or dealership that specializes in Japanese, Korean & domestic cars and if they recommend replacing the brake pads, I guarantee they will also recommend resurfacing the brake rotors. Go to a shop that specializes in European cars, I'd be shocked if they even had a lathe to do that job.
Just a suggestion, before you take your rotors/hubs to an independent to have them destroyed, take a sanding wheel and sand away the hard shiny surface (glazing) to address the noise. Resurfacing the brake rotors will get rid of the noise but your cost will be a pulsation in the brake pedal because someone took too much material off and when the rotors heat cycled became warped and you end of having to get new rotors anyway.
Good luck, let us know what happens.

Just as an FYI, it's fantastically rare for rotors to actually warp. 99.9% of the time pedal pulsing is caused by uneven pad transfer. During braking, some of the pad material embeds itself into the surface of the rotor. This is totally normal and actually desired.

If you like to sit at stop lights with your brakes clamped hard, especially if the brakes are on the hot side, a little extra pad material can sort of stick when you release. Do this often enough, and you can build nice little clusters of pad material. To make things worse, the brakes are "sticky" in these spots which increases the odds of stopping on one next time, making those individual spots build little peaks of pad material n the rotors higher and higher with each stop.

Best solution to avoid this is to not stand on the brakes anymore once you've stopped. Ease off on the pedal, use only enough pressure as needed. Even better is to roll ahead very slightly periodically to avoid being clamped on to the same spot.

I agree with the above - a light cut might help you temporarily, but it's best to just go with replacement and change your braking habits. This part I'm not as clear on, but I guess the uneven heating you've created can change the metallurgy in the rotor unevenly, and that means your problem will come back.

Good luck!

That was my understanding as well. My brother and I had a long conversation about the what and why of "warping" and his point was the same as yours. The only thing I can figure is someone was a bit hard on the brakes before I bought the car. I downshift to slow down and I'm not hard on the brake at stop lights. I'm going to see if I can get them turned and if not I guess I'll be paying the Porsche tax :D

Thanks for your input

Brakes are thousands of dollars cheaper than a transmission rebuild. Don't downshift to save brakes. That is crazy. The brakes are cheap and easy to replace. In 20+ years of owning my 911 I have never warped the rotors and I have done over 100 autoccrosses.