# Testing runout of "warped" rotors at home?



## phatvw (Aug 29, 2001)

I am getting the symptom of mildly "warped" brake rotors (slight vibration) when I hit the brakes hard at _very_ high speeds. I do not get the vibration at lower highway speeds or under lighter braking.
I suspect uneven wear of the rotor rather than pad deposits (see below). What is the recommended procedure to test the runout of various thicknesses around the rotor? I would like to do this myself rather than taking it to a shop. Any recommendations for inexpensive test devices would help out a lot! Would a simple measuring caliper do the trick?

BTW I have Ferodo DS2500 front pads and Hawk HPS rear pads which are known to not adhere much to the rotor surface when hot. The rotors are slotted 12.3" from ECS. Pads have been properly bedded and are never stomped on when waiting at a traffic light. Lug bolts are torqued to spec, etc, etc.


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## phatvw (Aug 29, 2001)

*Re: Testing runout of "warped" rotors at home? (phatvw)*

Here are some hits on google:
http://www.gti-vr6.net/library....html
http://www.talkaboutautos.com/....html


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## Racer_X (Jul 14, 2002)

*Re: Testing runout of "warped" rotors at home? (phatvw)*

You can use an inexpensive dial caliper. A micrometer is a little better. 
For thickness, just check at various points around the rotor. 
For runout, it's best to use a dial indicator. You can sort of get a rough idea of runout if you use a dail caliper with a "probe" that sticks out the end. You can put the body of the caliper in the saddle of a jack stand with the probe sticking out to some known measurement. Position it so the "probe" just touches the rotor, then turn the rotor and let it push the probe in or you push the probe out to touch the rotor if the rotor surface moves away from the caliper. It won't be the most precise measurment, but with some care you can get a good idea of what you are dealing with.


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## jxforxjeff (Jun 23, 2004)

*Re: Testing runout of "warped" rotors at home? (phatvw)*

use a dial indicator with a magnetic base. attatch the magnet to the rotor nut (if its on the axle) and just watch the needle.
thats the most accurate way.


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## phatvw (Aug 29, 2001)

*Re: Testing runout of "warped" rotors at home? (jxforxjeff)*

Thanks for the tips.
I've got a track day coming up and I don't want to take any chances with my brakes, so I just ordered a set of 4 brembro rotors (front+rear) for under $200.
I'll test the old ones later and see if they are salvageable.


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## phatvw (Aug 29, 2001)

*Re: Testing runout of "warped" rotors at home? (phatvw)*

So after playing with the slotted rotors I originally thought were warped, I ended up taking them on the racetrack!
They aren't warped at all, I'm just really sensitive to the slotting. It vibrates ever so slightly and hums really loud under heavy braking. The hum has gotten quite a bit louder since the pads have worn in and even louder after I installed camber plates with hard strut mounts. They still work fine and I didn't really have to buy those plain brembo rotors.
I still don't like the feel of the slots though and will swap in the regular rotors when these are worn out.


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