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

[Mark Strangways]

The rotor is designed to float on the hat.
So, torque is a very important factor. So are the many small bolts and funny
looking nuts that allow you to reach torque but still allow the rotors to
float.
I don't know if you used the new ones with the rotors you bought, I assume
you got your rotors complete with the Porsche hats from the factory. I would
strongly suggest you don't re-use the old fasteners, use  the new ones that
shipped with the rotors.
Second, you will need to index the rotors on the hat. Try placing the rotor
on the hat 180 degrees from what it is now.

There is a factory porches sheet that is on the bira site that gives the
proper torque values and sequences.

Mark S
----- Original Message ----- 
From: "Sandy Sligh" <sdslig at yahoo.com>
To: <s-car-list at audifans.com>
Sent: Wednesday, February 11, 2004 6:20 PM
Subject: [s-cars] Big Reds making Sandy red in the face...


> 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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