2009 BMW M3: Learning to Ignore Driveline Lash

i'm with lsd...maybe driveline lash isn't quite the right descriptor for the situation.

perhaps take the car to a friendly shop with a lift and make sure all the relevant bits are properly tightened under the car? might as well look into it in case something actually is wrong.

pretty sure there are a few m3 owners here who could provide some insight into this.

I seem to remember something about the E46 M3 having some sort of trick differential that was notorious for having a "clunking" noise when shifting in lower gears, perhaps the E90 is similar? (I can't remember where I heard that or even if it was a reliable source, so take that with a grain of salt)

I think all cars have some driveline lash. It's more noticeable in manual transmission cars, because there is no torque converter to absorb the lash.

I'd imagine that a car like this - track-oriented, snappy, precise - probably has a pretty heavy duty clutchplate, which would magnify some of the things you describe. I've heard it described as chatter - the small clunks and jerks of the transmission and clutch. I've only ever felt it in manual transmission cars with aftermarket clutch kits though, and I've never driven an M. So take this all with a grain of salt or two.

"It's more noticeable in manual transmission cars, because there is no torque converter to absorb the lash. "

Doesn't the transmission, manual or not, qualify as a torque converter?

My '03 M3 makes that sound (it's a manual), but i personally love it! It gives the car a very mechanical and organic feel that I think is missing from a lot of newer cars.

As an owner of one of the earlier E92 M3 Coupes built (Spring 08 production) I agree completely that there is a lot of mechanical noise at low speeds although not sure that drive line lash is the correct term. I remember my 2005 M3 Coupe and my 2001 before that having similiar characterstics but the 08 seems a little worse. I recently drove a DCT equipped 2010 M3 for a couple of days and although I never thought I would say this or feel this way, I actually preferred it to the manual because it elimimated that "clunking" through the driveline. I noticed that Porsche's in particular don't have this characteristic so I am a bit surprised that BMW couldn't have done better.

A tip from E9x M3 owners- don't shift before 3k rpms in the first gear. Apparently that smooths out a lot of the roughness in the 1-2 shift.

My DCT sedan has the same noise. M3Post forum members seem to all agree that this is normal. I believe the manual says so too but don't quote me on that.
Personally I love it. If I want it nice and quiet I'd have kept my 06 325i--great car, but not nearly as much fun.

It's normal. I own almost the same exact car. If you really want to hear something, roll down the window in a parking garage and listen to the differential while turning tightly. LSD groans. The instructors at the M school in SC told me they all do it. I first noticed it in the m5.

banhugh, the torque converter is actually a coupling/ transfer device between the transmission and engine in an automatic transmission vehicle. As you know, the clutch is in place of this in a manual transmission vehicle.

torque converters allow the transmission to slip at all times below certain speeds and slip at idle so that the engine doesn't stall

This post was very useful. One person learned what a torque converter is and one person learned what driveline lash isn't.

Few things....

my experience with driveline lash is multitudinous, and I'll list out the ways:

1. Recent drive-by-wire setups with a sharp transition point. In my 2006 Civic SI, this is particularly pronounced in low-speeds in low-gears and moreso when cold. The car bucks between no throttle and partial throttle, and feels like the drivetrain is transmitting power in a surging fashion. Just a byproduct of poor drive by wire programming, not true driveline lash. (Also occurs in my 2008 Legacy GT, to a far lesser extent).

2. True driveline lash as the gears in the drivetrain rattle slightly under the power pulses of the engine's delivery through the flywheel. This becomes more prevalent in many hard-sprung clutches with single-mass flywheels.

A flywheel acts as a damping force on the engine (it's a heavy mass at the end of the crankshaft). A dual-mass flywheel is actually two masses that are "sprung" together and allow for pulses to be absorbed while still delivering power smoothly through the spinning flywheel (i.e. the flywheel absorbs the surges of pistons delivering their power, rather than transmitting it to the clutch/trans).

A single-mass flywheel does not absorb these surges, so the next step is the clutch. Clutches have "sprung" hubs, where the middle of the clutch usually has ~4 springs that can absorb some of the twisting and then halting motion of the engine's power pulses. If the clutches spring rates are very hard (takes alot of force to compress them), then the power still "pulses" through the transmission.

In order for gears to mesh, they can't be impenetrably tight to each other. As long as power is being delivered, the gears press against each other and the power is seamless. But when "pulses" go through the system, the gears press against each other, relax, press, relax.

And sometimes you get noise. Especially in low gears, when the power pulses come much slower.

The advantage of setups with more noise is, typically, a much crisper power delivery or in some cases (i.e. straight-cut gears) a much stronger way of building the gears.

But sometimes it's also just greater build tolerances between gears and one car will have more noise than another. Kinda like oil consumption on some cars....not a sign anything is wrong, could even be a manufacturer build specification making it happen, but kinda annoys you nonetheless.

Joe

Off topic: what would the insurance be per year for this M3, for a 30-something? I've heard insanely expensive quotes for sports coupes such as the base Corvette topping $4k in LA. I wonder how much the premium would be for this hot number...

My G35 (I know, apples to oranges) costs under $1k in the Seattle area, but that's bundled with house insurance.

^ I'd call a lot of different insurance companies for quotes.
I've had quotes ranging from $1750 to $8500, with an average of $4500. This is for a married 30-something couple, NYC residents, homeowners, no tickets, but with one single-car mishap with insurance payout of $900. Liability coverage is high but so is deductible on damages.
Some insurance companies won't even want to insure the M3 unless it's a weekend car.
Good luck.

Some insurance companies won't even want to insure the M3

WOW.

Thanks for the info, E90! I am just learning how wildly illogical insurance rates seem to be. Do M3 drivers REALLY crash that much more than other drivers? I just don't get it. Seriously, I just put it together. That's why tuners get started. Insurance. They cannot insure factory hot rods.

^ @jederino:
"I am just learning how wildly illogical insurance rates seem to be. Do M3 drivers REALLY crash that much more than other drivers?"

Judging from the crash stories on M3Post, I have to say... YES!
It seems, on average, one member gets his car totaled every other week.

We are with Allhate insurance. We are in Louisiana which has high rates. The m3 is a third car for us, insured as a weekend car, under 12k per year. We have max liability. We are also insuring a 2007 Tahoe LTZ and 2008 Nissan Crew cab Frontier as our dailys. All three are pretty close at 1200 yr. per car.