Measuring rotor runout (was: UFO problems)
sscalmanini at yahoo.com
Thu Jun 13 22:16:33 EDT 2002
There's a simple tool you can make or have made to
easily measure rotor runout with a dial indicator. A
machinest friend made one for me a few years ago when
I was dealing with my UFO runout problem. It made
measuring runout a breeze.
Cut a 1/4" x 3/4" bar of metal (I used Al) about 1 ft.
long. Half-round one end along the 3/4" dimension.
In the center of that half-round, drill and tap a hole
for a 1/4-20 thread. Attach the bar to the lug on the
back of the dial indicator with a 1/4-20 bolt (5/8"
long) and a few flat or wavy washers between the bolt
head and lug; tighten the bolt just enough to enable
the dial indicator to be turned by hand around the end
of the bar.
(If you haven't access to a tap, drill the hole .250
diameter and use a longer 1/4-20 bolt and a nut.)
Clamp the bar to the stabilizer (torsion bar?) under
the front end with vice-grips so the dial indicator is
roughly in the center of its travel, turning the
indicator around the end of the bar as necessary to
make it roughly square to the surface of the rotor.
Now you can rotate the tire by hand and easily read
the runout (first jack up the front end onto jack
stands, silly). Up to .002" runout is normal; over
~.005-.007 will vibrate the steering wheel.
(I never tried this for wheel runout so I don't know
if the bar can be clamped appropriately for that.)
FWIW, I solved my vibration problems temporarily by
having my UFOs turned at a machine shop in San Jose
(see Chris's site for details). I hope I solved it
permanently last year by changing tires from BFG TAs
(no longer made) to Michelin Pilots (for twice the
price and less warranted mileage; oh well, quality
original front-end components
no vibes since mounting Michelin Pilots
Do you have access to a dial indicator? If so, check
your rotor runout first. If not, jurry rig a pointer
attached to the caliper mounting to eyeball rotor run
out. While doing this check for wheel bearing
which can contribute to apparent rotor run out.
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