ThreeTTwo

Okay, after the tire shell game (new front, swap two corners) there's still a 'weakness' for the left.

Alignment specs seem good to all who read them.

So yesterday I threw on a set of A6 16x7's with a known good-running set of low-mileage Michelins (I drove them from new).

Car still drifts left. So... now we know it's the chassis, made worse if the tires are funky, but not caused by them -- correct?

But here's what's weird: Sometimes no pull at all, sometimes the steering wheel moves left under braking. Sometimes there's a drift, sometimes there isn't.

This sounds like a loose suspension piece, but I hear no shifting or clunking noises -- as I would suspect -- as the loading changes to upset the alignment.

And in general, it feels like there's normal resistance to a right turn, but the steering wheel feels overboosted to the left. But only sometimes.

This also seems -- seems -- RPM-related, just to throw another set of variables into the mix. Steady-state cruising at 35MPH/2500RPM seems to result in the next stop being a pull to the left.

I also may have to suspect brakes. There's a light squeal from one set of pads, occasionally.

Going to the dealer again. Telling them "Intermittent drift to left, on deceleration/braking from 30MPH in 'S' mode/D2. Slight and intermittent noise from brake pads. Steering 'favors' left turns (less resistance, sometimes).

Is this truly odd? Or is there an 'Aha!' forming in your minds? Again, the car has 28K miles, and we've had it from new, with no major hits we're aware of.

As always, thanks for the counsel!

PlainRuss

If it was me, I'd also be checking SAI and IA as well.

ThreeTTwo

(Googled some info):

"Both SAI and IA are measured similar to a caster sweep. When the SAI reading is combined with the camber reading, the sum of the two angles equals the IA. Using SAI/IA and camber will help identify a bent or shifted component."

"The optimum setting on all vehicles for setback is zero, so either a positive or negative setback reading indicates cradle shifting or some other component has moved."

I'll add this to the list... thanks, Russ!

diagnosticator1

is a fault in the hydraulic servo valve regulating the power steering fluid pressure applied to the steering rack. That valve is positioned by the steering shaft and directs pressurized hydraulic fluid to the rack depending on steering shaft rotation direction and rotation rate. The hydraulic pressure is limited by a force feedback loop. If the servo valve, or other involved steering component is faulty, then unbalanced steering forces will be created that result in the drifting you describe. The specific behaviors you noticed as not normal, the intermittent and speed related symptoms, particularly the unequal steering assist on left and right turns, implicates the steering system as responsible for provoking the car's drifting problems. Further, there is a history of steering rack replacements under warranty on B6 A4.