Avoiding warped rotors

[Wade Nelson]

Here's a simple way to reduce your chance of warped rotors / pedal pulsation when you do a brake job.

The root CAUSE of warped rotors (disk thickness variation) is runout in the hub itself. Basically, what that means is the hub, hence the rotor, is TILTED, ever so slightly.

(If you want to argue the cause of warped rotors, google "warped dtv" and then get back with me)

You can put a dial indicator on the rotor (1/4" from outside edge) , and index the rotor, basically, try it in the 4 different positions on the hub and see which produces the least runout. If you're not a professional mechanic, you probably don't have the slick setup for doing this.

The easiest thing to do is this: When installing new rotors, take a zip disk, (3m abrasive pad on a die grinder) and be sure you remove absolutely all rust, grit, and grime from where the rotor mates to the hub, so they mate perfectly! Even a speck of rust can tilt the rotor ever so slightly, causing runout.

Do that and chances are you'll avoid warpage even if you don't bother indexing.

The reason on-car brake lathes got so popular is no matter how the rotor is tilted, they're gonna cut it in-plane.

But with new rotors selling for $25 or less, who would bother measuring and cutting an old one anymore?

[Walter Moore]

Where does one get rotors for a Z car for $25? Most places want three to four times that.

[Zed Head]

Wade's on a roll, it's hard to keep up...

Rock Auto - http://www.classiczcars.com/forums/thread46074.html

Edit - but it seems the sub $25 price is only for the later Zs. Which is odd considering a previous discussion about whether or not the 240Z and 280Z hubs and rotors are different.

Edit 2 - Still not sure that they're different, not sure why Rock Auto has two parts and two prices... http://www.carpartsmanual.com/datsunS30/DatsunZIndex/Axle/FrontAxle/tabid/1728/Default.aspx

Edited May 12, 2012 by Zed Head
link cleanup

[Arne]

Considering that he posted this in the ZX forums, I'm not surprised that the price is good for later cars.

[doradox]

The root CAUSE of warped rotors (disk thickness variation) is runout in the hub itself.

DTV and warped are not different terms for the same thing. Warped rotors cause DTV but are not DTV. Perpetuating the use of the phrase "warped rotors" when one means DTV doesn't help clear up the confusion. Maybe you meant to say "The root CAUSE of warped rotors and consequently DTV, which causes pedal pulsation, is runout in the ROTOR itself". It's not hub run-out that is the most likely cause but a mismatch between the mating surface of the rotor and hub due to dirt, rust, or whatever between the hub and rotor. Hub run-out is not measured at the rotor it's measured at the hub. Rotor run-out is measured at the rotor. Yes, I am being pedantic, but this is the internet and inaccurate information gets regurgitated over and over in the blink of an eye.

Steve

[Walter Moore]

Sorry, I didn't check the forum where this thread was located. For all you S130 guys looks like you win on this one. The price at Rock Auto for the rotor on the early car is nearly twice what was listed above.

[Zed Head]

Actually, any Z from 1974 on (I assume from the big bumper 260Z) gets cheap rotors. It's the 240Zs that have the expensive ones. But it's still not clear what the difference is between the two.