L8 Apex

My father-in-law and I recently replaced the brakes on his 993 (4 weeks ago?). Now when applying light braking the steering wheel wobbles back and forth. When applying the brakes firmly it doesn't seem to wobble. While slowing for a stop sign it will do it around 20-25 miles per hour. It didn't do this before we replaced the pads. The rotors were turned when we did the pad replacement, and there is no pulsation in the pedal while braking. The car is definitely due for new tires. I think we put Textar pads on it, and they didn't have the cups to seat the pads like the OEM pads that we took off.

Any ideas what might be causing this? Tires, pads, or other?

Thanks,
Jason

Bradford

When you apply the brakes and the steering wheel vibrates or wobbles, it usually means that the rotors are warped.

L8 Apex

My experience with my Audi has been that warped rotors cause pulsation in the brake pedal, especially when braking from high speeds, and I'm not feeling any of that in this car. The rotors were turned but maybe they could have been turned incorrectly?

Thanks,
Jason

Dudley

My guess would be tires and they are the easiest to rule out. Swap out the tires (especially front) with a friend's and see.

the_buch

Perhaps you deposited some new brake pad material onto the rotors during the pad break-in ... what procedure did you follow for this?

Bull

I would not turn 993 rotors, replace them.

ca993twin

I have never been a proponent of turning rotors. You can't "turn-out" a warped rotor, all you accomplish is getting rid of the lateral grooves. These really have no negative impact on the brakes, once the pads are bedded into the grooves. In fact.... the grooves actually provide slightly more pad/rotor contact area. The downside to turning rotors is losing thickness and mass, which is way more important then worrying about those grooves. Well, I guess I should add that turning rotors does get rid of the coating of brake "varnish"... but this is also accomplished with a good cleaning/light sanding.

97Targa

When I was at a PCA tech session the Brembo rep told us not to turn the brake rotors. His comments were:" If they are bad or out of spec. , replace them. Turned rotors are even more prone to warping due to the decreased thickness of the metal".
OBTW, if you replace the rotors, from what I've read (here & other places) stay away from the zimmerman brand replacement rotors.

Robin 993DX

Jason,

Vibration from the steering wheel while braking is most likly from warped rotor, but it is difficult to believe only after 4 weeks on a new set of rotor. Also you would feel the vibration during high speed braking instead of low speed.

I would suggest you check the tightness of the wheel lug nuts, and tires as a likly area that is causing the problem.

Unbalanced lug nut torque can also cause the problem you are experiencing.

Robin

deltawedge

Having turned rotors for a living (not entirely fun), turning rotors does require a proper technique since it is a precise machining operation (and all turning machines have their own peculiarities). That said, having the rotors turned does not always mean that the run out will be less than before or even within spec. Not that it can't be done; it just depends on the skill of the operator and their familiarity with the equipment used.

Since I no longer have access to turning equipment, I always buy new rotors when changing pads, since the cost of new rotors is relatively low when compared to the aggravation of taking it all apart again (IMHO).

On the positive side, the symptoms you describe may be caused by an installation or pad bedding error, which can likely be resolved.

As mentioned previously, an uneven accumulation of pad material on the rotor can cause enough run-out to make the steering wobble. I believe there is a procedure that can remedy this, but do not have any experience with it (others may know).

Other possible causes could be the mounting of the rotor against the hub (ie particles in between the two surfaces) or the torqueing of the wheel nuts. I have had the symptoms you describe due to the wheel nuts being installed with an air gun and not being properly sequenced. The fix was to loosen the wheel nuts and then retighten (and properly torqued).

Good luck and Happy New Year!

epj993

I'd also add that you should replace with cast rotors vs. drilled. For the street, stock rotors are fine.

FWIW, you might also have some buildup of brake dust inside rotor vanes and holes. This happened to me and created a vibration in the 55-60mph range. Flushing with high pressure from a hose nozzle will clean them out.

Caveman

In the UK we have Porsche specialists that have special rigs that they use to skim the rotors in-situ. It's not a perfect solution but it does prolong the use of the discs.

Cheers,

David

ZombiePorsche44

Ditto what the others said about new rotors................

PS: rotors normally only warp due to very very high temps.....kind of makes you wonder who cooked the ones that are on the car?

sidned

May be a build up of brake dust in the rotors. Clean them out and see if that helps.

TroyN

I've seen posts here about cars with worn a-arm bushings that resulted in a vibration upon braking. Just an alternative possibility if one of the other suggestions is not the answer. Good luck...