EbonyC4S

Last June the local Porsche service department replaced both front rotors on warranty due to varied thicknesses around each circumference (the rears are fine). They were not warped (no run out). The new rotors were smooth as silk until 2,000 miles were driven. Then they started to show signs of judder again. They now have 3,500 miles on them and the steering wheel waggles visibly while braking even from slow speeds. The deceleration under braking is pulsating. The service tech found the same issues and has come up with no cause either time. He has recommended replacement again.
Has a problem like this shown up with anyone else? The car has not been tracked. Driving has been routine travel with no hard braking. What could possibly cause a set of rotors to fail in 3,500 miles?
TIA! I'm hoping the Rennlist brethren can help figure out what the techs can't.

awrryan

What kind of pads?

yvesvidal

There may be some play in the front arm bushings, that is exacerbated when you brake.

Yves

EbonyC4S

OEM, believed to be factory installed. Dealer tech states they're well within spec. The car was purchased CPO @ 9,500 miles. Now @ 21,500.

EbonyC4S

Thx Yves. Would worn bushings and other suspension/steering linkages also show up as vibration during times other than braking? This issue is solely incidental to brake application.
Stuart

cerbomark

Was first thinking a caliper but the pads would probably be ruined. Then thinking wheel bearing but you had 2000 good miles with the new rotors. A improper pad installation, I forgot the shims on one of my cars and it did what you are describing intermittently ... I m sure the tech would know if it s the rust film you get on a car not driven a lot and put away wet such as washing for long periods. The rust transfers to the pad sometimes causing the feeling you describe. I had that once too on a MB and the dealer had to replace rotors and told me it was a one time warranty and I needed to drive the car more LOL.... Just some thoughts.
PS/ or as mentioned something not right in the front end. The braking forces might cause what you don t feel when not under braking.

EbonyC4S

Thx for your input cerbomark.
These rotors were mic'ed which showed thickness variations of .16mm and .14mm on the fronts only. Spec is .02mm max. No pad stains have been noted. Stuart