time to replace rotors?

terryb · 10-07-2006, 01:04 PM

I'm in the process of removing the front calipers on my '88 coupe to try my hand at rebuilding them because the pistons are sticking. I hear that while you're in there it's a good idea measure the rotor thickness. They measured:

LF 23.30, RF 23.36
LR 22.66, RR 22.71

None of the rotors are smooth but all have a series of concentric ridges and grooves. I'm planning to remove them and have them turned but are the rears too close to the minimum thickness of 22mm? I've never had rotors turned before so I don't know how much material normally comes off. Should I just replace the rears? The car has 120k miles and they look like original rotors.

Thanks.

Nine9six · Nine9six's Garage

Terry,
Are you replacing the brake pads? If not, dont bother having your rotors turned. If you do have them turned, figure on replacing the pads as well. Otherwise you will be pressing grooved pads against your nice flat, freshly machined rotors.

Lots of guys here will say that standard Carrera rotors are to inexpensive to have turned. I on the other hand, believe that if the engineers had not wanted the rotors to be turned, they wouldn't have given minimum thicknesses. Others claim these thichnesses are given for wear.

Like anything else, it all depends on what you are doing with your car. Daily driver, AX, DE, track toy...

Also, you want to make sure the guy turning the rotors respects the datum face or plane. This means they need to stone the face of the machine that your rotors get mounted to. Otherwise they will be machining in error. The same needs to be done with the mount face of the rotors.

This can be checked by running a dial indicator on the mount face of the machine, and double checked, by putting a dial indicator on your rotors after remounting to your car. Runnout should not more than .004"

terryb · 10-07-2006, 03:34 PM

Nine9six - Thanks for the reply. Yes, I'm replacing pads (Ferodo 2500's) so I'm told this is a good time to turn the rotors. As far as how I use the car, I've been doing an AX every month or so as well as daily driving.

I agree about using a quality person to do work on our cars. A Pelican member who I trust has recommended a nearby shop to turn the front rotors. I think I've decided that since the rears are somewhat close to minimum I'll just get new ones for $180 from our host.

Thank you for the info regarding runout.