Warped Rotor Myth (by Beandip)

[TomoHawk]

I just had my 280Z at a Meineke place to "surface the rotor" that was shuddering while braking. I said the re was a "sticky spot" from the brake pad material. The tech guy drives my car around a parking lot, then tells me "You have a warped rotor." After I informed him that there's no such thing as a warped rotor he gives me a look like I'm telling him!? Then he says I need both lower ball joints $500 per pair) and a tie-rod end (new tierods from my Mustang rack install)

YOUR ROTORS ARE WARPED FROM OVERHEATING THE ROTORS WHILE DRIVING.

OK, maybe the ball joints ($200 each!) are about ready to be changed, but those people still tell me I need two new rotors & pads (rotors & pads come in "matched sets?")

Finally, they guy tells me if I did get new rotors & pads, I wouldn't have to do anything epecial for pad brake-in.

Yeah, right.

thxZ

[twsutt]

Tomo,

Did you expect anything different from a guy at a "chain store" garage?

Hell would have to freeze over before I take my Z to Meineke, Pep Boys, Jiffy Lube (except for a state inspection), Brake Check, etc. The average monkeys that they tend to hire are too ham-fisted to work on any car as classic as a Z.

Please tell me that you walked away.

[jmortensen]

Having put many many rotors on a lathe and actually SEEN the cutter hit one side of the rotor and not the opposite side, and seen it reversed 180 degrees awawy on the rotor, I'm a bit perplexed by this whole "deposit on the rotor" scenario. That said I also have all of Carroll Smith's books, and I'd consider myself a fan of his. Whether you call it a deposit or a warp, cutting the rotor on a lathe will indeed remove the problem. Unfortunately it will also make the rotor thinner, and more likely to develop the same problem quicker the next time in my experience.

Having passed the ASE test on brakes, I can tell you that they don't subscribe to the deposit on the rotors theory, or at least they didn't when I took the test in the early 90's. So telling an ASE certified mechanic that there is no such thing as a warped rotor is an exercise in futility, and to keep going to different shops telling them that there is no such thing is about as useful as repeatedly slamming your head into a wall.

To fix the problem use different pads. Whether the pads are depositing material on the rotor or warping it is irrelevant. Using a different pad is going to be the solution. You can either cut the rotors or replace them. I made a decision not to turn rotors on my own vehicles a while back, so I just replace them, but cutting will work.

[TomoHawk]

Did you expect anything different from a guy at a "chain store" garage? .... The average monkeys that they tend to hire are too ham-fisted to work on any car as classic as a Z.

Please tell me that you walked away.

Yeah, I asked for a written quote, and asked for the car back because I didn't have the time to wait. I will givethem a call when I am ready forthe service.

I do know a guy ( greasy blue coveralls and face, dirty little shop on the corner of some quiet street) who will tell you things (a little) more honestly. I think I will go there and get the rotors turned again, if there's enough material left.

jmortensen-

I'm not sure which pads are on there right now. Probably generic or Bendix ones. Is there a suggestion on what pads to get or ask for?

Darn- I forgot to tell them to hand-torque the wheel nuts.

thxZ

[jmortensen]

I don't know much about street pads. I'd say stay away from Metal Masters as I had a warpage issue with them on two different vehicles, but that's about the best I can do.

[sleepyzzz]

my Nissan dealer has a brake lathe that turns the rotors while still on the car, so that everything is true to the hub. is this really the best way to do the rotors? they claim that this is the only way to guarantee no run out or shimmy when braking.

[jmortensen]

my Nissan dealer has a brake lathe that turns the rotors while still on the car, so that everything is true to the hub. is this really the best way to do the rotors? they claim that this is the only way to guarantee no run out or shimmy when braking.

On a Z the rotor gets bolted to the hub, so when you put it in a lathe you use the hub and it's all bolted together. So you basically get the same effect. Most newer cars have slip on rotors. On that type of setup the on car lathe has a real advantage.

It is true however that most brake lathe spindles are bent because stupid mechanics slam down heavy drums and rotors on them (I know because I used to be a stupid mechanic who didn't realize the damage this caused), so the on the car lathe might be better in that respect. If you had a straight spindle on the brake lathe though, there should be no real difference between doing it on the car vs off the car for a bolt on rotor like a Z has.

[Walter Moore]

my Nissan dealer has a brake lathe that turns the rotors while still on the car, so that everything is true to the hub. is this really the best way to do the rotors? they claim that this is the only way to guarantee no run out or shimmy when braking.

It certainly guarantees that you are not spinning the rotor with it mounted to an uncontrolled surface. With rotors that are removable from the hub (like on a Z car) there is a risk that someone will clamp it to a lathe with either the center or square-up surface locating on a part of the rotor that isn't tightly controlled. That will cause the finished cut to be out of square to the calipers when it is mounted back on the car.

Personally, I never turn brake rotors. If they are within the specified minimum thickness I just replace the pads. I know that in doing that the car will shake and shimmy under some braking loads for the first 3 to 5 thousand miles, but it always goes away eventually. I am just cheap, and have found that rotors that are not turned every time will last MANY thousands of miles longer than rotors that are "trued up" every time.

If in the business of repairing brakes, then I would probably want to turn the rotors every time, because it would reduce my warranty costs.

(And increase my long term part business.)

[jmortensen]

It would be more work to separate the rotor from the hub to turn it. I've never seen it done, although I suppose you might run across a particularly stupid mechanic or a lathe that is missing the correct adapter for the hub bearings I guess...

[TomoHawk]

The last time I had a rotor from my Z turned, it was removed from the hub. The hub was repacked before reassembly, which isn't so bad a thing, but maybe not that much needed.

I'm off to the dirty brake guy to see what he has to say- BBL

thxZ

[doradox]

No such thing as a warped brake disc? Well I guess that could be true under a strict definition of warped and disc. I define warped as the disc being not parallel with the plane that is perpendicular to the axis of rotation of the hub. The "disc" part of the rotor may not be warped but can still wobble instead of spin true. It's the whole spinning assembly that needs to be true, not just the disc part if the rotor. I do agree that the shudder most of us feel is stuff on the friction surface of the disc and not "warp". I've seen rotors that were "warped" by my definition not give the slightest hint that there was any problem.

Steve

[jmortensen]

The last time I had a rotor from my Z turned, it was removed from the hub. The hub was repacked before reassembly, which isn't so bad a thing, but maybe not that much needed.

I'm having a hard time believing that a mechanic would do this. IME the Z rotors don't usually come off the hub too easily, so it really is something to be avoided if at all possible.

Normally to turn a Z rotor a mechanic would remove the wheel bearings and wipe out the grease from the hub, then turn the rotors with the hub on the lathe, then repack the bearings and reinstall in the hub and reinstall the hub and rotor on the car. Is that not what happened on your brake job?

The way you wrote that out made me think that you thought repacking the bearings was necessary due to the removal of the rotor from the hub, which is not the case.