LAH_

I will be replacing my front pads soon on my 2016 A4 B9 TDI Quattro with fixed calipers (1LC). I don't have the brake pads wear warning yet but I believe it is imminent.

I've been experiencing strong vibrations when braking exclusively at around 140km/h speeds. The vibrations seem stronger with hot brakes but I can not confirm this definitively.

Afters today's morning commute of around 50km's at high speeds with some high speed braking for testing purposes I noticed these spots on the front right rotor when I parked. Seems like hot spots or brake material transfer to me but I would be glad if someone with more experience could comment.

A couple of months ago I tried to remedy the vibration problem by applying the procedure described in the workshop manual to clean up the rotors, thinking the vibrations could be because of uneven brake material transfer. I don't remember the exact process but it described a series of slow downs from a certain speed, very much like a bedding in process for new pads and rotors. Didn't help much with the vibrations though.

I haven't measured my rotors yet but they are probably in limits albeit by a small margin.

The car has 65k km's on the clock now. Previous owner told me he had the brake pads changed right before I bought it from him at around 38k on the clock. I believe the rotors are from the factory and the current pads (probably ferodo's) should be the second set they've ever seen.

my questions are;

1. Would you replace these discs even though they have remaining thickness?
2. Could these spots on the disk be the reason for the vibrations? If so I am willing to replace them to get rid of the vibs.
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Thinking this would only be a brake pad job, I already purchased a set of trw pads through a good deal. Now that the rotors are in question, I cannot find any trw rotors in stock to match the pads. A parts dealer I spoke with today trashed trw as a brand which led me regretting the purchase a little. I am inclined towards ferodo rotors which are currently available in stock. So the remainder of the questions are

3. Would trw pads work fine on ferodo rotors or should I better match the pad and rotor brands?
4. Provided that I'm in limits with the rotors, would a pad change help with the vibrations?

Sorry for the long story and thanks for any input!

Cheers


Front right rotor

Front right rotor2

acpRS3

I'm not an expert, but that does not look like material transfer to me. Material transfer usually looks like smears of material around the full circumference of the rotor, not isolated spots.

One thing to check: Do your control arm bushings look ok? On my 2014 A7, I have twice had shuddering under braking from highway speeds, and thought it was the rotors, but both times it turned out to be worn control arms (upper, then lower).

If it's not the control arms, I'm willing to bet it's the rotors. To answer your questions:
-A pad change will not help if the rotors are warped
-You can absolutely mix and match pads and rotors between manufacturers (it's actually pretty rare that you would have pads and rotors from the same manufacturer, even straight from the factory)
-In the US, TRW is a bit of a budget brand with not the best reputation. People seem to like Zimmerman if that is sold near you. They are not that expensive, at least here in the US.

LAH_

Thanks for the reply, after further reading and your supporting comment, I am inclined to believe these are heat spots indeed.

From visual inspection only, I am guessing my upper control arm bushings are on their way out. I have a set ready from lemförder for when they actually fail. However I don't think the vibrations are related to the bushing since it's strictly speed dependent and I have no other indications of bushing wear, uneven tire wear, knocking etc.

Interesting finding on your A7, what was the milage when you have the arms replaced?

I have pretty much decided to replace the rotors with ferodos. I believe my current pads are also ferodos from what I can see with limited access.

I bought the trw's thinking they're OEM and the irresistible price they had. Returning them will be a hassle for me so I will probably end up using. My only concern is if they will ruin the new rotors. I'm hoping OEM pads won't do any harm.

Zimmermans are sold at pretty much the same price as the rest of the OEM bunch but not as low as the trws.

I'm thinking rotors are more critical to the system since pads are easy to swap in case they turn out to be crap.

acpRS3

The uppers went at around 50,000 miles, lowers at 75,000. But the car spent the first 40,000 miles driving mostly around New York City, which I suspect is much harder on the suspension than "normal" driving.

Your thinking makes sense to me - good luck with the change!

nataliarelish998

Heat spot on the material is different between material properties and transfer issue