brian a

I have been thinking about replacing them myself to save some money, I keep hearing they are real easy and I have a friend to help me if I get over my head. But I have been told by acquaintances, who are NOT mechanics, that all rotors have to be machined before installation. Is this true?
Thanks,
Brian

SteveAngry

On old ones it is costwise to "turn" them if thier is enough material left. Helps get a little more life out of them...IMHO

HTH
Steve Ankney
88 5000
Holland, Michigan

Silver Streakin'

Replacing the rotors is not a difficult job as long as you take your time and use the correct tools when taking things off/apart. Once you've done one, then the other 3 will get easier - hopefully.

Once you get the wheel off, then the caliper out of the way, the rotor will just slide off. Put the new one on, put the caliper and wheel back on. Make sure you use a torque wrench to put the lug nuts back on or you'll worp the new rotors. Are you putting new pads on too? If not, make sure the old pads don't have grooves in them from the old rotors or that they're "chunked" as I've heard them called. Smooth them out or you'll end up putting groves on your new rotors. I don't know what to suggest to smooth them out with, since I've never done that before. Fine grade sand-paper, maybe?

As for a rotor being "machined" as you've been told. That refers to the existing rotors being smoothed out. You can have that professionally done, but only if you have something left on your rotors to work with. For example, I know with mine, they're 25mm thick when new and 23mm is the suggested limit, which would fail at a State inspection nor would you want them that low for further poor performance reasons. I would assume if there was 24.5mm left that they could be smoothed out (machined)for smoothing braking, which stops your car quicker. However, if your rotors are like mine, which are at 23.1mm, then there's not enough left to smooth out to keep it above the 23mm limit. I hope this helps and didn't make it more confusing.

The bottom line is, if there's enough left on the rotor to smooth out to keep you above the limit, then do that before buying new ones, if you want to save the money.

If it was me, since I would rather have new and better performing parts, I'd just buy new ones that out perform the OE parts, e.g. ATE power discs or Zimmermann "cross-drilled" ones. Especially since you'd have to put out $$ to have each of them machined, you might as when just get new ones, right?

Good Luck!

Seattle Scott

the rotors on my 97 A6 are only good for one "turning" and then they are too thin to turn again.

Have also read somewhere that if you have warped rotors (heat damaged, they get so hot they warp) that turning won't do a lot of good. The theory is a warped rotor will have soft and hard spots on it and wear un-evenly. I really don't know.

I never heard of warping a rotor from not torquing it correctly but you do have to torque the rotors on.

Anyway, it is an easy job, especially if you do one side at a time so you can use one side as a referance if you get lost, confused, scared or whatever.

Mean Gene 4.2

Why in any case should rotors need to be repeatedly turned? I have perpetually had trouble with warped rotors on my '87 5KSQ. The rotors had just been machined when I bought the car seven years ago; it didn't take long for them to warp. Pentagon-grade (at least expense-wise) rotors were installed by the dealer, were carefully broken in...and warped. After a while I gave up on them, bought a second set from Blaufergnügen, had them expertly installed, carefully broke them in, and...you get the picture. I doubt it's my driving style; no other car I've owned has had this problem. Any thoughts, anyone? I must admit that I'm tired of lumpy braking.

TIREGUY

I'ld try a different pad.

Silver Streakin'

I would assume that putting your 2 + 2 would = warped rotors. If they're not torqued probably you end with spots where the pads hit tighter than others causing those areas to heat up and other areas to have possible gaps in pad pressure which these areas would be less hot under braking, thus causing them to warp (worp..whatever the frickin' spelling of this non-technical word is). I would think that keeping the rotors smooth would keep the pads smooth. I would think that brake pressure would also be a factor in causing unever rotor and pad wear. I get the brake fluid bled properly every 2 years or 30k, which ever comes first, done to also help keep things in spec.

It is difficult to say what causes warping and uneven wear since there are so many factors in braking. To me, preventative maintenance is the key and using the right parts. Once you start guessing and using non-OE parts, then you're taking chances unless the aftermarket part is a good replacement, e.g. ATE power discs and Zimmermann rotors and redbox pads, etc., etc.

I've also heard of rotating your rotors. Personally, I would think this would make them wear down even faster.

DMS-Audi Quattro

ATE are great rotors and ready to install
it should say on the box

machining your rotors just wears them in a little

DMS-Audi Quattro

when ever you turn your rotors you affect the integrity of the rotor i think your only soppose to turn rotors somthing like 2 times.. if youve done it more than that. that could be your problem... in the bently manual it tells exactly how much you can surface your rotors (checking with a micrometer)

Seattle Scott

You don't have to turn any rotors religiously. New ones should never need turning. Old ones can be measured and examined to determine if they need turning. Many people just turn them or replace them anyway.

You SHOULD use a torque wrench on various brake parts to insure the bolts don't "back" out and the compression forces are equal.

Rotor warping is caused by uneven heating and or cooling. Don't brake like a maniac and you should be OK.

Make sure your friend is there to help you. You also haven't said what kind of car and if you plan on doing all four corners of the car. If you are only doing the front, no problem. If you are doing rear disc brakes you may need some more information.

Are you going to replace the pads too? Are you going to flush the brake fluid?

You can use the Search function of the forum to retrive all kinds of information on brakes. Use it and you will learn a lot.

If you don't have a manual for the car I reccomend you get it and read it before doing the job. Go to http://www.rb.com

You can go here to see how brakes work :<ul><li><a href="http://www.howstuffworks.com/category.htm?cat=Brake">How Brakes Work</a></li></ul>