I've been experiencing a strange phenomenon on my '09 MCS. The car has a slight pull to the right but only when going less than 18 MPH. Anything above that the car pulls straight ahead and does not drift to the left or right. I can even let go of the wheel and the car will stay straight and true. This is really driving me nuts and I'd like to get some opinions. Here's some other info:

-Had alignment 3 months ago and still exhibited the problem even the day after the alignment. No I didn't hit a huge pothole.

-Checked for excessive rubbing in the front passenger side wheel well and there are no rub marks on the inside of the tire and wheel.

-Car has factory mechanical LSD.

-I know the steering angle sensor isn't working. Whenever I start the car the DSC immediately turns off and I get warnings on the dash about it. Whenever using the turn signals, making a 90 degree turn, I have to manually shut off the turn signal instead of it going off automatically.

-I have replaced both front wheel speed sensors.

-Car exhibited issue BEFORE I reflashed ECU. Not tuners fault!

I have a couple of theories. First, I think there is some stupid logic in the ECU that may be applying my front passenger side brakes during this speed range and making the car pull to the right. I can't verify this since there isn't excessive wear on that rotor and also the pull isn't excessive enough to probably cause that wear. The only other thing I can think of is the LSD itself. Could there be something mechanically in the differential that is doing this? This could get expensive!

This is kind of an annoyance more than anything. The car drives perfectly on the track and during spirited street driving. It's when I'm in stop and go that it's kind of irritating.

 

More clues. Just had the car up on jack stands and started engine with car in neutral. Right wheel is spinning almost at an idling pace and the left wheel is stationary. WTF?! Isn't neutral supposed to me literally that... neutral?!

 

You need to either get your SZL (includes steering wheel angle sensor) module replaced or may only need to be re-calibrated. The EPS (electric power steering module) does use this information to work properly. Until the SZL is working properly, you will continue to experience problems.

 

This is not unusual as the the gears are engaged all the time but rotating on their bearings. When in neutral there is enough drag to cause the output shaft to rotate. The differential will then send that to whichever wheel has the less drag; doesn't take much.

Using the Kiss philosophy (keep it simple ...) check that one of the tires has not slipped its belt. This can cause a car to pull. Easy check is to swap the tires side to side.

 

I talked with my dad yesterday and he mentioned exactly what you pointed out about gears still moving on their bearings even while in neutral. I never even thought about this. Good to know that a second source verified the science behind it too. Thanks!

On the steering issue, I think it all comes down to the steering angle sensor. I'll just put up with it till I have to sell the car someday.