Urs6 vibration under brakes

[ottawa coupe]

Not sure if this should be here or in the steering section but here goes:

I've been chasing an issue in my s6 for a bit now and i am running out of clear causes. The car drives great, tracks well, no issues, untill i hit the brakes. When i do, the steering wheel shakes quite badly. Only thru the wheel, ZERO vibration in the pedal.

Looking for causes. What i have done so far is check for loose bits in suspension (iDID find the jam nut on one tie rod loose, tightening DID help). Rebalance and rotate tires, inspect all 4 corners for anything obvious.

The issue persists.

I am on diy coilovers with blake dunham's camber plates up front and qa1 coilovers in the back. Brakes are brembo 17z on 323mm rotors up front, 310mm rotors out back with stock calipers. The fronts are drilled n slotted.

My next inspection will be to check the alignment. As mentioned above, i did find a loose jam nut on a tie rod so i now doubt9 the quality of the alignment that was done. I should add that it pulls to the right under brakes since i tightened the jam nut

But beyond that i am kinda stumped.... maybe fire the parts cannon and get quality plain rotors and pads for the front? But if it were brakes, i should feel something thru the pedal not the wheel?

Subframe bushings???

I'm going to replace the tie rod that was loose as i don't relish the idea of it having bounced around on the threads for god knows how long...

[Tractor Dave]

Likely a warped brake disc (rotors). You often don't feel this via the brake pedal at all. The cause is either brakes getting very hot, track day or very spirited drive or more likely a sticking caliper. I have this very symptom now on our old b5 passat. It doesn't get used much and I'm often experiencing sticking calipers. Just had this last week and now the dreaded vibration in braking via the steering wheel. I can just feel on the brake pedal at very low speed only. New calipers and discs on order.
An old mechanic friend also warned me years ago that doing up wheel bolts using a high powered air gun can actually warp discs (rotors) if done one bolt fully tight at a time.

[ottawa coupe]

Weird, i had always thought you'd always feel brake issues thru the pedal.

I'm going to set up the strings and check the alignment today. Bezos got 25 more of my dollars for a laser temp sensor that arrives tomorrow and i'll see if that points me in the direction of brakes.

[Antsa]

One option might also be if not warped discs, uneven brake pad material trasfer around the disc circumference. This causes uneven friction around the disc that could be the cause of your mentioned symptoms.

This can happen if the the rotors are hot and brake is applied at standstill.

[ottawa coupe]

So, did 2 things after coffee this morning: took it for a properly focused test drive and i set up the strings. As a result i currently think i have 2 issues. The first is that 3/4 tires are pointing straight. The 4th has significant toe out. It happens to be the wheel that had the loose jam nut. So, that's something to sort.

But the brake thing possibly has increasing weight here.

Drove barefoot to ensure nothing is felt thru the pedal and that continues to hold true.

But what i DID note is that from stone cold, the first couple of stops are silky smooth. Then it all goes to crap. So it would seem that as the rotor grows when heated through, it does so unevenly? I also did notice when coming to a stop that the car seemed to judder a bit on the last few tire rotations.... like there wasn't consistent friction at the pad/rotor interface.

So, with a bit of luck i'll get at the alignment issue today and see how that works out. Then when the temp gun gets here tomorrow, the things felt today may present themselves as temp variations. That SHOULD get to the bottom of it.

Right?!

Too early for beer yet?!

[ottawa coupe]

Played with the offending corner. Made it much worse lol but i was trying to do it on the ground. Will fix it later this weekend on my lift.

The main thing is the issue was unaffected. So i guess i am lookin at new brake pads/rotors.

The good news is that once i have gotten this pointing straight again, i can get back on to the coupe.

[Henkjan]

could be a rim that's not straight (either the rim itself or not mounted flat)

[ottawa coupe]

Wheels checked and rebalanced, they're fine. Problem persists with other wheels too.hopefully gonna fix the alignment tonight and rotors/pads will get ordered next week

[vag_noob]

I had that exact problem caused by a bad wheel alignment, bad toe setup on the front. Fixed by alignment on a different machine when I took it back. Never had it occur again.