Turning brake rotors?

[makaio]

I'm getting ready to put new brake pads on the front of my car. The rotors still have plenty of meat left on them, but have some grooves. I asked one of the mechanics here at work, and he said never to have rotors turned. Just put the new pads in and go. This mechanic used to work at an independent Porsche specialist shop, so I tend to believe him. But I had always heard it was fine to have rotors turned.

What do you think?

Should I have the rotors turned?

Or just throw the new pads in?

I'm planning on packing the front wheel bearings while I'm at it.

[gchappel]

I am by no means an expert, but I have had rotors turned without any problems. I understand the arguement that the main reason to turn rotors is warping due to heat, if you turn the rotor there is less mass left, so they are more prone to overheat the next time.
It certainly does not hurt the rotors- one of the better race mechanics in the area turns new rotors before mounting.
At least measure your rotors- measure run out with a dial gauge and thickness. You didn't say if you were having any problems, like "surging" when you brake. If you have no problems, and still have enough thickness on your rotors- just replace the pads.
Gary

[gr8fl4porsche]

I recently read on rennlist that you should not turn rotors.

I quit turning them years ago on my other cars due to the fact that they warp very easily after turning and usually only cost a few bucks more for new ones. Not true with P-cars though - have you priced a set of rotors?

On my motorcycles and 4 wheelers I just slap on new pads and bleed the brakes - never had to turn or replace - they stop on a dime and give you nine cents change.

[bell]

it was always my understanding that if you have new pads the rotor should be resurfaced in order for the new break pad to bed in. i've done this on our race cars and on my personal cars and always experience better brake pad longevity.

my .02
bell
85'911

[bjola]

Never turned my rotors when replacing pads. When the rotors get too bad I just replace them. Never experienced a problem and I use my car a lot for track days.

[jabb]

I am done turning rotors... If they are not warped or badly gouged just put on the new pads and go.... Just check the thickness. Just did my wifes Saab a couple of months ago new pads and go..... No complaints an ocassional squeak.

[Jdub]

I suppose by turning them you can get rid of that irritating ridge that sits at the outside edge. Of course, if they are this far gone maybe they ought to be replaced?

One thing: on my MGB I was told that the rotors should not be turned, but rather radially brushed by something akin to grinding stones (holy cavemen Batman!). Maybe someone who knows more about this process can comment.

John

[Rot 911]

John, why would you ever turn the rotors on an MGB when for $60 you can get TWO new front rotors and a set of front brake pads?

[Jdub]

Kurt:

I shoulda known you'd pipe in Mr. '72 chromebumper; at least my '69 had THREE wipers (yes, it's true!).

Did you ever hear the same thing about grind/brushing versus spin cutting? I ended up having the rotors "brushed" in lieu of the RIDICULOUSLY low price I could have paid for new. What I learned from that brake job was 1)rotors can glow red 2)rubber lines trap fluid and prevent release.

What did I know? Heck, what do I know NOW? ;>

John

[Don Wohlfarth]

"It certainly does not hurt the rotors- one of the better race mechanics in the area turns new rotors before mounting."

I don't think he is turning these rotors, but instead is simply trueing them up. If he has to turn them he should be sending them back and finding another vendor.
Don't forget the bedding process for pads and rotors. New pads on old rotors, new rotors on old pads. If you are driving the car on the street you'll never see track temps so I wouldn't go thru this process. Different story for a track car where the bedding process can become critical due to overheating.
Rotors should be considered a disposable item. If they've got deep enough groove in them to need turning they won't have enough thickness to meet spec when you're finished. If they do meet spec there's a good chance they didn't have deep enough grooves to need turning.

My front discs are warped and cause the steering wheel to vibrate under braking. They have only covered 25000KM. Should I have them turned or replace them? Huge price difference.

[Don Wohlfarth]

Mikkel, it sounds like at least one if not both rotors are warped.
I had posted that rotors are cheap. You posted that there was a huge difference between new rotors and having them turned.
I did a search of Pelican Parts and found brake rotors. 74-83 are
$50 ea and 84-89 are $60 ea for Zimmerman OEM rotors. If you were in the US you might want to look there.
Also on the rotor page were the thickness of new rotors and the recommended replacement thickness of old ones. 74-77 new
20.0mm replace at 18.0mm, 78-83 new 20.0mm rep 18.5mm, 84-89 new 24.0mm rep 22.0mm.
With new rotors at 120 bucks a pair and only being able to remove a maximum of 2mm from a rotor why would anyone want to turn their rotors?

[makaio]

Well I didn't have my rotors turned. Just yanked the old pads out, and put the new ones in. The hardest part was pushing the pistons back into the calipers.

[old_skul]

New rotors are pretty easy, too. All you have to do is:

Yank the pads.
Unbolt the caliper. Move it to the side.
Unscrew 4 screws holding the rotor on.

That's it. Reassembly is the reverse of removal. And you can get decent $60 front rotors.