Brake Run-out

Can someone give me a good explanation (or direct me to a resource) of brake run-out and why it is commonly recommended to "turn" brake rotors even though the rotor looks in good shape, i.e. no scoring, etc?

Thanks...

Reply to
David Glass
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Runout is the side-to side wobble you'll get when your rotors get old. Since you have a Camery, you'd be best just to replace them rather than turn them. Turning rotors (stripping some metal off to even them up) makes them thinner and they get hot quicker. Heat makes them warp (changing the runout).

They're inexpensive and not worth turning. Replacing them on every other or every third pair of pads is a good idea.

Reply to
Gary L. Burnore

Brake runout is another term for rotor warpage. A warped rotor will cause a shuddering sensation when braking and on Toyotas, you will need to replace both rotors because "turning" them will remove too much rotor material and the warpage will re-occur. If there are no symptoms of warped rotors and the rotors are in good shape, with no excessive rust around the outside and no scoring, then I would not turn the rotors when replacing the pads because you will just shorten the rotor life. If the rotor is in good condition and its thickness is above the minimum stamped on the rotor, then scuffing the surface with medium grit sandpaper or using a Scotch pad on a die grinder or drill will produce very good results.

When turning rotors, they are placed (one at a time) on a brake lathe which rotates the rotor while a cutting bit shaves off some material on both faces of the rotor. This is also referred to as machining rotors.

The reason some shops recommend turning rotors when doing a brake job is to provide a nice uniform surface for the brake pads. to remove any glazing on the surface of the rotor, and to remove what some people call "hot spots" on the face of the rotor, where excessive heat has changed the properties of the metal. Scuffing with sandpaper or a Scotch pad will remove any glazing and if there truly are "hot spots" on the rotor where it has discolored (usually blue) then turning them is unlikely to remove them so you're better off replacing them anyway and determining what caused the hot spots in the first place, ie., frozen slides on the calipers or letting the pads get down to bare metal.

Reply to
Ray O

I've heard that over or uneven torqueing of the lug nuts will do this too?

Reply to
Gord Beaman

If you decide to replace them avoid those MADE IN INDIA -- very inferior metal!

Reply to
Wolfgang

Depending on the type of rotor, yes. Usually the fronts. The rears have extra bulk because of the drums for the emergency brakes so they're not as often effected.

Reply to
Gary L. Burnore

Uneven or over-torqueing of the lug nuts can warp rotors and drums. Also riding the brake pedal for a long time and hitting a deep puddle with very hot brakes.

Reply to
Ray O

"David Glass" wrote in news:Htx8e.14997$ snipped-for-privacy@typhoon.sonic.net:

Best explanation I've seen yet:

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Reply to
TeGGer®

Turning the rotors was once considered proper service. But these days the rotors are thinner (lighter) than they once were, and many cars have rotors that can not be turned because this would put them below the minimum specification for safe thickness.

Let's say, for example, the rotor is stamped with 120mm on the edge. This means that the minimum thickness is 120mm. If they are sitting now at 125, then the shop can only remove .005mm of material before the rotors are less than the specification, and it is not allowed for them to be less, so the shop can't turn them and they must be replaced in that case.

If the rotors are warped - this causes the steering wheel to shake (sometimes violently) back and forth when stopping - then the shop has to calculate how much warpage there is, then determine if they cut of the high spots and leave the low ones so the rotors are flat again, will there be enough material left. Usually there is not enough material to clean up a warped rotor.

If the rotors have grooves cut in them, or slight ridges, then they probably do not need to be turned. The pads will seat around these ridges, but you have to take steps to seat them properly or the rotors will over heat and this causes them to warp. When you install new pads and do not turn the rotors, then you need to lightly apply the brakes several times to seat them If you go out and have to brake hard and the pads are not seated yet, then the heat can cause the rotors to warp.

You shouldn't be alarmed with the prospect of replacing rotors, I have seen them advertised for as low as $10. I put new rotors on my BMW, and they cost $50 each. This is not a huge cost, and you should reasonably expect rotors to last for two or three sets of brake pads.

Reply to
Jeff Strickland

idiots with air wrenches probably warp more rotors than any other cause.

Reply to
JeB

-Ted

Reply to
Ted Johnson

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