Brake runout tool fixture? (1 Viewer)

[John E Davies]

I bought a 1 inch dial indicator and a magnetic base to check the runout on my LX brake rotors. The only way I could mount the base so that the indicator tip would reach the rotor face was to clamp it (magnetically) to the caliper. This wasn't too great since the caliper floats around. The base really ought to be mounted on the axle or spring or somewhere close by that doesn't move.

Has anyone made a mounting fixture for measuring rotor runout? I was thinking of maybe using a plate of 1/4 inch steel C clamped or bolted to.... what?

Thanks for any help, and pics if you have them. Maybe a link?

Thanks.

BTW - my aftermarket rotors are toast - the left rear is warped .017 inches, so I am going to re-do the rears with new OEM rotors and pads from cruiserdan. He was most helpful.

John

 

[medtro]

Do you have any metal object that you can move close to the rotor for the base mount? May be a tool box?

 

[Scamper]

Hi John,

I wouldn't mount it to anything that might move while testing the runout (like the floating portion of the caliper), but there is no magic location for this--it just has to be a stable location for the duration of the measurment. The FSM shows the base of the indicator mounted somewhere near the lower shock mount while measureing the runout on the inboard surface of the rotor, though the picture is a tad lacking in detail. Have you been trying to measure the runout on the outboard surface of the rotor? No real need for this.

Just how short is the arm on your magnetic base? Rather than mount it to the caliper, couldn't you mount it to something more solid like the knuckle housing or even the upper or lower knuckle bearing cap?

 

[RavenTai]

I have a mac tools base and indicator that worked well on the rears, I was able to stick it to the frame and reach, have not tried it on the fronts yet, it is a 2 arm style not much for the quality of it so I cannot recomend it but it works

 

[IdahoDoug]

I simply use a screwdriver and hold it against something handy so you can see the extent of the runout - no measurement. Go around the car a couple laps and compare them if you've got a brake shimmy or pulse and it won't be long before you'll easily identify one or more that's really a wobbling disk. Just did this a couple weeks ago on the Subaru and quickly identified a rear rotor when I'd fully expected a front from the behavior. Cost me $10 to have it lightly turned as I immediately pulled the rotor and dropped it at their shop. An hour later - smooth braking.

I'm all for precision if you've got a subtle or persistent problem. But I think a decision can be made based on this simple technique to identify a problem rotor. Unfortunately, it won't work on a 2wd vehicle as you have no way to spin non driven rotors, but...

DougM

DougM

 

[alia176]

Curious,

Are you guys running the 80 on four jack stands with the tires off to get the run out?

In the cae of a 2wd, can't you simply stop (wedging something between tire and ground) the spinning wheel to get the other one to spin?

 

[e9999]

yup, any big object you bring next to the wheel should do. One of those foldable workbenches that clamp things down? Vise on a low stool? Ladder?

best: Anvil?

E

 

[RavenTai]

with a dial indicator it is not necessary to have high speed of rotation, just put both tires of one axle in the air (locker disengaged) reinstall some of the lug nuts without the wheel to hold the rotor squarely on the hub and turn it by hand

I assume the screwdriver method Doug outlines requires driving speed? Don’t know never tried it.


Lodging a solid object between the ground and wheel of a truck on jack stands with the engine running in gear may get you a Darwin award :whoops:

 

[IdahoDoug]

I really don't recommend this at all due to varying abilities, but yes I idle w/o wheels on up in the air. Works for me and saves the usual "idiot fee" of having a mechanic simply yank all four rotors, machine them all and hand you a bill for 150 clams after trying to talk you into replacing all pads, calipers, axles, heater blower and anything else even remotely related to the brakes.

DougM