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      04-22-2014, 03:27 PM   #1
ADD_It_Up
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Does this sound like a rear diff problem?

Not sure where to post this so I'll try here.

I picked up a used 2010 E92 about a month ago from a dealer in another state and drove it home. Have put about 3500 milies on it since. Didn't notice any issues with it on the drive back except a little more road feeback than I am used to which I attributed to the 20" wheels on this car.

At this point though I am seeing some odd behavior that I need to sort out ASAP. Almost not sure how to describe it, but here goes. If I wind it up in say 3rd gear (it's a 6MT), and then just let off the gas and let the engine braking kick in, the car kind of shimmies back and forth for a second. The degree of sway seems to vary depending on how high up in the rev range I am at the time, but it can be very pronounced. Like if I took a video of myself from the back seat, you would see my head and shoulders kind of jerk from side to side.

It almost feels like the vehicle is pulling in different directions independently at each wheel. Very strange. I thought maybe one or more of the wheels were coming loose and checked the lugs but they are tight. Honestly I am not sure if I am dealing with some kind of steering issue or driveline issue. I am thinking maybe some kind of rear differential synchronization problem since I can always reproduce it on decel with engine braking, but that could just by a symptom. If I wind it up and then depress the clutch pedal this doesn't happen so it does seem related to engine braking one way or the other.

I will almost certainly need to get the vehicle into the dealer, but wanted to try to get some ideas of what could cause this before I do. Anyone ever seen anything like this?

Notable details / mods:

2010 E92 M3 6MT (53k miles)
- 20" HRE wheels
- KW V3 coilovers
- Eisenmann exhaust

Thanks!
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      04-22-2014, 05:04 PM   #2
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I'd be tempted to have a good weighted alignment done on it and while they're under there, check for any loose or worn suspension components. Especially with the aftermarket coilovers (a lot of guys lower the car and don't touch the alignment afterwards). Rear toe could be way out-of-spec. I've upgraded differentials on a couple of my cars, but never had any experience with the symptoms you describe, so no help there.

I had a full alignment done last week on my M3 and it is definitely more stable and planted in high-speed sweeping turns. A worthy tune-up for a reasonable cost.
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      04-22-2014, 05:57 PM   #3
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I'd get it in the air and see if anything is loose. Try to wiggle each wheel and check the suspension/subframe components.
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      Yesterday, 02:13 AM   #4
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Quote:
Originally Posted by Beemdog View Post
I'd be tempted to have a good weighted alignment done on it and while they're under there, check for any loose or worn suspension components. Especially with the aftermarket coilovers (a lot of guys lower the car and don't touch the alignment afterwards). Rear toe could be way out-of-spec. .
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      Yesterday, 06:00 AM   #5
MilehighM3
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Sounds like an alignment issue to me as well
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      Yesterday, 02:21 PM   #6
ADD_It_Up
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Thanks for the suggestions! I don't have access to a lift or the expertise and tools to do an alignment but will look into it. It seemed odd that the problem came on so quickly after picking up the car. My impression was that the guy I bought it from was more into the car looking good than driving it hard, and I've definitely been stretching it's legs a bit so maybe I've managed to shake something loose suspension-wise...
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      Yesterday, 03:57 PM   #7
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Keep in mind that the alignment for E9x cars is recommended to be done with specific amount of weight added to the front seats and a full tank of gas (or weight added to the trunk). Some cheapie tire shops will ignore that part. I had to probe around a bit to find out who was highly-regarded locally to do performance alignments and do them right.
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