2008 M3 e92 Knocking/banging noise from rear under heavy acceleration/wheelspin!

[Pietu]

Hey guys.

I have noticed that my M3 makes this noise when accelerated heavily and the lsd takes on. It almost sounds like the lsd is "catching and releasing" in a fast pace, almost similar cutting sound than when doing full abs braking.

Initially I thought it was the DSC limiting the spin but tested this with DSC off and I still got the noise! I also tested by dumping the clutch from stand still at about 4000-5000 rpm but that way got normal wheelspin with no banging noise. So the noise only happens when accelerating hard from low speeds and also on low friction (wet) surfaces.

I do not normally mistreat my car or try to deliberately wheel spin it but have gotten this noise a few times recently when accelerating on wet roads. On normal driving conditions I don't get it unless accelerating extremely hard on first or second gear. The car is manual and has 44k miles.

Any idea what might be causing this noise? Is my diff broken or could it be the bushings or quido? I'm taking the car in this week for brake fluid change and software problem so will mention this but any insight on the matter might help locate the problem!

[RudyP]

Sounds like axle tramp to me.

[Pietu]

Originally Posted by RudyP

Sounds like axle tramp to me.

If you are right, any idea what could be the main cause?

[Reznick]

Yeah it sounds like axle tramp. Have someone watch you do it . Thats a pretty quick way to confirm the wheels are fighting so hard for traction they're trying to rip themselves out from under the car.Hopefully thats all it is.Good luck

[Reznick]

Originally Posted by Pietu

If you are right, any idea what could be the main cause?

Axle tramp is the just the cars tires and rear suspension trying to cope with the power you're throwing at it and get traction at the same time. The tires initially spin, then get traction then spin then traction ...it causes a small chain reaction and you get the rear tires basically bouncing up and down fighting for traction. There are ways to overcome this but short of turning your M3 into a drag car , I'd leave it alone and stop spinning the tires

[RudyP]

Originally Posted by Reznick

Axle tramp is the just the cars tires and rear suspension trying to cope with the power you're throwing at it and get traction at the same time. The tires initially spin, then get traction then spin then traction ...it causes a small chain reaction and you get the rear tires basically bouncing up and down fighting for traction. There are ways to overcome this but short of turning your M3 into a drag car , I'd leave it alone and stop spinning the tires

This. This car isn't really set up for burnouts and such. A solid axle rear suspension pony car (e.g., Mustang) would be a lot better for this type of stuff but an M3 is much better around corners and on uneven surfaces. If you really care, there are ways of modifying your suspension that could get rid of the axle tramp (often different damping rates, addition of stabilizer links in the suspension, etc...) but then you're building a drag car.

[M3PO]

Yep, sounds like wheel hop. It's very bad for the car. You could break the diff bolts which would result in a bent subframe and a serious repair bill.

[Pietu]

Thanks for your replies guys. Wheel hop does sound like the right diagnosis, it was just weird as none of my earlier cars have had wheel hop in similar conditions. (z3m, 330ci) I suppose it's the M3's suspension combined with the lsd.

Will mention it at the dealership tomorrow and ask them to verify everything is tight and good to go in the diff and rear suspension. As I mentioned its not normal for me to do burnouts, the wheel hop only happened during rainy slippery conditions.

[Khrishna]

Originally Posted by RudyP

This. This car isn't really set up for burnouts and such. A solid axle rear suspension pony car (e.g., Mustang) would be a lot better for this type of stuff but an M3 is much better around corners and on uneven surfaces. If you really care, there are ways of modifying your suspension that could get rid of the axle tramp (often different damping rates, addition of stabilizer links in the suspension, etc...) but then you're building a drag car.

+10000 ...solid diff mounts as welll

OP this a great way to destroy your diff and diff mounts..You cant consistently burnout in this car, stock, without doing damage, despite what anyone tells you.

[CarbonFoot]

Just out of curiosity - what kind of tires are you running and what's the outside temperature when you get this wheel hopping/traction issue?

I've seen a number of M3s effortlessly roast their tires without experiencing any hop - mine included. I think something else is at play here.

[Pietu]

Originally Posted by CarbonFoot

Just out of curiosity - what kind of tires are you running and what's the outside temperature when you get this wheel hopping/traction issue?

I've seen a number of M3s effortlessly roast their tires without experiencing any hop - mine included. I think something else is at play here.

Running stock 265/40/18 and temperatures around 10-15 celsius with wet roads. As I said, if I intend to wheelspin my car on a dry road by dumping the clutch my car will also spin its wheels easily without wheelhop. This wheelhop only happened in slippery conditions. Makes me wonder if the possible uneven traction combined with lsd causes it?

[atermechi]

That wheel hope no doubt, my car is the same way, it only happens when it is slippery outside.

[X2Board]

Cold tires and low traction will do that. The PS2's don't like anything below 45 degrees.

[M3PO]

Originally Posted by CarbonFoot

Just out of curiosity - what kind of tires are you running and what's the outside temperature when you get this wheel hopping/traction issue?

I've seen a number of M3s effortlessly roast their tires without experiencing any hop - mine included. I think something else is at play here.

I think it has a lot to do with how aggressively the car is launched. You have to hit a "resonant frequency" so to speak to create the hop. Launch below or above that (like in a burnout) and you don't create the hop.