UFO Brakes

["Paul C. Waterloo" <74543.407@compuserve.com>]

After the recent discussions about UFO's, I looked them up in the Bently for the
first time. Couple interesting things to report:

Brake Caliper - the outline drawing says "cannot be repaired, replace if
necessary"...that seems kinda weird, you can't overhaul them? Anybody ever try?

There is a section on "Steering Wheel Shimmy During Braking", it has three
things you can do to fix it (they are outlined in this order):

CHECK CONTROL ARM BUSHINGS
1. Remove wheels, disconnect brake pad sensors, remove front pads, remove
calipers, but do not disconnect.

2. If you have less than 40K on your car, inspect the inner and outer control
arm bushings for cracking, splitting and deterioration.

3. Replace as necessary.

4. If you have more than 40K on your car, replace both front inner and outer
front control arm bushings. For those who don't know what a control arm bushing
is, it's the bar that the front sway bar and lower ball joint are attached to.
The bushings that they are talking about are where the sway bar goes through the
control arm, and where the control arm attaches to the subframe (I think
subframe is the correct term) of the car.

TRUING OF FRONT BRAKE ROTORS

1. True front brake rotors with an on-the-car brake lathe.

2. Note: if an on-the-car brake lathe is not available, replace rotors.

3. FYI - brake disc thickness new 25 mm (0.750"), brake disc wear thickness -
23mm (0.690")

WHEN NEW BRAKE ROTORS ARE REQUIRED

1. Thoroughly clean contact surfaces of brake rotor and hub.

2. Install using all lug bolts with suitable spacers.

3. Tighten lug bolts diagonally in stages to 29 lb-ft.

4. Attach dial indicator to measure brake rotor runout.

5. Rotate rotor and record runout.

6. Remove brake rotor and remount after rotating rotor to next lug bolt hole. 

7. Check rotor runout.

8. Continue remounting rotor checking runout at each lug bolt position.
        ---- Maximum rotor runout 0.06mm (0.002")

9. Mount rotor in position where lowest runout was achieved.

10. Mark hub and rotor with center punch as mounted in lowest running position.

MORALE OF THE STORY

>From what I can see, if you car has front end shimmy, I would first check brake
rotor runout and determine what it is, maximum new is 0.002", I wouldn't want to
go past 0.004" or maybe 0.006"?

If rotor runout is acceptable, go after your bushings. If you are going to go in
and do a brake job, why not replace the bushings as a matter of good maintenance
practices. I doubt they cost very much, especially when comparing them to the
price of rotors and pads.

This procedure will help you determine the root cause of the problem so you can
then fix it!

Paul

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Paul Waterloo
Colchester, CT

91 200q

EMAIL: 74543.407@compuserve.com
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