[s-cars] Big Reds making Sandy red in the face...

[Sandy Sligh]

Ok, this email will be part Sandy's-an-idiot and
Sandy's-a-newb. Whichever is worse, who knows.

SO. The S4 fails tech inspection due to worn-out front
rotors (993tt). No problem, I'll go pick up a new set
and put them on myself. How hard could it be really. 

I get the rotors in my hot little hands, pull off the
old rotors which are cracked inside edge to outside
(nice work, Bruce!! Thats some hard drivin!)  Pop the
rotor hats out and install said rotor hats onto brand
new rotors. WHee!!! Going pretty good. 

A week or so later I develop two vibrations. One felt
through the steering wheel (small amplitude) when
cruising at 120kph and higher, the second(medium
amplitude) when lightly braking from 100kph and down
to about 40kph. This second one I feel much more in
the steering wheel and also through the brake pedal.
With the hands off the wheel and braking, the steering
wheel noticably rocks back and forth rapidly, maybe
3/4" to 1" in each direction.  

"There is no WAY I've warped these rotors!", Sandy
cries.

I pull them off, pull out the hats and clean up the
mating surfaces considerably, mostly scraping off what
I assume was built up pad material.  Reinstall the
rotors.. same deal, vibrations are unchanged. (BTW,
I've been very methodically about torquing my wheels
correctly.  In a star pattern, first to 45ft-lbs and
then to 90. )

Off they come again and I notice outlines of the brake
pads imprinted on the new rotors.. AH HA! Stoptech's
brake FAQ tells me what that is! I remove those rotors
and reserve them for later scrubbing with garnet paper
per Stoptech's suggestions (hopefully a new set is not
in order. $$$$)  In the meantime, I reinstall the old
rotors and plan on babying them until I either am
ready to try the new set again or break down and buy
another set.

Well, low and behold, the old rotors are displaying
similar albeit slightly better symptoms.

Questions:

A) Do the sources of my vibrations reside elsewhere?

B) Am I missing a crucial installation step, i.e. a
specific torque pattern on the rotor hat bolts? (I
devised a type of star pattern and just cranked them
down till they all felt equally tight) 

C) Do I need to go back over the mating surfaces again
and damn well make sure they are clean and flat?

D) Maybe because I didnt' change the pads at the same
time? (why would this affect running the old rotors..
)

E) Something else entirely? 

Please, anyone with BTDTs or suggestions unleash them
upon me.  I've spent more than a few nights in my
parking garage pulling wheels, pulling calipers,
pulling rotors, cleanings, tightening, reinstalling,
wash, rinse, repeat. Help make me smarter and the ride
out the the shop.


Thanks in advance


Sandy

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