I have been told by Volvo and by several mechanics Volvo disc brake rotors CAN NOT be turned to remove imperfections. If this is true I would like for someone to explain to me why. Thanks in advance.

 

They tell you that because when the rotors are new they are cut crosshatched which ones cut like that are not supposed to be cut. They will make funny noises after being cut.

But the shop I work in now I have to cut them. I am not really happy about it but I have to do it to keep my job.

We have had alot of them come right back warped again after cutting them as well.

 

You CAN apply the crosshatched finish to a rotor cut on a normal lathe- you use a special DA grinder attachment that attaches to the lathe. It turns in the opposite direction from the rotor, and you buff the rotor with it at the end of cutting. This will greatly reduce noise. However... thinner rotors on ANY car is asking for warpage- less metal= smaller heatsink= higher temps= warping. My personal take on the whole thing is this: contrary to what they used to teach (they're teaching it differently now- don't turn rotors unless necessary!) it's not necessary to turn rotors unless they are warped or scored. If there's no noticeable pedal pulsation, and the finish is nice and smooth, don't bother turning, because all you'll do is remove metal. There's no benefit to it at that point. Sometimes I'll apply a light crosshatch finish with a grinder to help with breaking in the new pads, but I only do that on cars that are really noise- prone or have really hard pads. Otherwise, just leave it alone if the rotors look good and aren't warped. Rotors are supposed to be smooth- that allows for maximum surface area. Cut rotors feel "grippier" to your hands, of course- because your hands are soft. Brake pads are hard, and when the rotor has a rough,machined finish, it simply means there's less for the pad to grab on to, and it reduces braking effectiveness until the rotors have worn smooth again. One more thing- Volvos chew rotors anyway. You'll rarely get more than 2 sets of pads out of them. That's another reason Volvo rotors tend to warp when they have been turned- they're WAY too thin for the hard, aggressive pad material Volvo uses.

 

OK. I agree with the not turning if they are not damaged. Never have understood why you took metal off the rotor, if it was not warped.

What I can't find is what is the minimum thickness for a rotor. I have not been able to find a decent shop manual on the S70. I have looked but not found one that tells much about the car. Can someone give me an idea of the min thickness of the rotor. Thanks in advance for the help.

 

Most rotors will have it stamped on them. If you cannot find it the spec is Min at pad replacement is 23.8 total min is 23.0MM

 

You mean to tell me Volvo thinks that their pads only wear .8 mm total from the rotor in one life cycle? Um... try like 2 mm or more. I swear, they put diamond powder in their pads or something.

 

I know the specs are wacky.

 

Tech is right with the measurements. General rule of thumb for volvos is .8mm more then the rotor minimum thickness on any of there cars except the older models ( 240/740/940). Thats for the fronts. The rears depends on the car, and for the non awd s70's is 8.9mm when replacing pads.