Rumble Under Hard Acceleration (e46 M3)

[DSC-off]

I have been experiencing a strange vibration/rumbling in my '02 SMG M3 under hard acceleration. When I'm hard on the throttle (mostly in gears 1-3) there is a rough vibration from the rear of the car, I want to say it's from the rightish side but that could potentially be my imagination (definitely rear though). The rumble typically only lasts 300-500 RPM under hard acceleration (which goes by very quickly), it occurs somewhere in the 3500-4500 RPM range. If I am accelerating slowly through this RPM range it does not seem to occur. It is like a hard stutter, almost like a series of ABS pulses or some sort of slip/grab. This rumble/stutter seems to have gotten more severe recently.

The Diff oil was changed (with the friction modifier) maybe 15,000 miles ago (when I bought the car). After doing some reading on various forums I was pretty convinced that the rumbling issue was caused by the central support bearing or the guibo, so I had both replaced last week. Sadly this did not resolve the issue.

Other random information (not sure if any of it's relevant): The car has had a noticeable whine from the diff whenever your off the throttle (its been doing it since I bought it more than a year ago), but various people have told me that it's normal for these diffs to make some noise. I had the sub-frame reinforced with the Turner kit about 6ish months ago. I had the RTABs replaced (stock bushings with limiters) about 3 months ago. The car throws a flat tire warning maybe once every ~3 weeks, I clear it and it goes away. Transmission is SMG and I'm betting the clutch has never been replaced, the car has about 103k miles on it (but it does pass the 6th gear-40mph and floor it test).


I am pretty stumped as to what might be causing this rumble/vibration, but it is really worrying me. Can anyone point me in the right direction for what might be causing this? I really hate taking anything to the stealership, but this problem seems to beyond the knowledge level of my local indys.

[LivesNearCostco]

I would say it's definitely guibo and/or CSB, because that's what caused these same symptoms in my E46 (non-M). Except you just replaced those. Given that, other possibilities are unbalanced wheel, bent wheel, broken transmission mounts, broken motor mounts, bad wheel bearing, bad U-joint on driveshaft and unbalanced driveshaft. If the shop replacing the CSB took apart the driveshaft and put it together differently, that could have unbalanced it.

I've heard a whine is normal in some LSDs, not sure if it's normal in yours.

[DSC-off]

Would an unbalanced/bent wheel manifest in such specific circumstances? I thought it would cause more general vibrations all the time. I was assuming that any sort of wheel imbalance would be a steady and very noticeable shudder at higher speeds. The car is reasonably smooth well above a hundred. Wouldn't a wheel bearing also be very wheel speed dependant, not engine speed dependant?

I had read that drive shaft unbalancing or bad U-joints could maybe cause something like this. This may be a dumb question but I've never taken the drive shaft apart on this car, is it a finite amount of configurations (like two) that the drive shaft can be re-assembled in or is it infinite configurations? Namely, would there be any chance of re-assembling it right, or if there were no marks made to track the "balanced" configuration am i just shooting in the dark?

I doubt the shop that did the CSB/Guibo did anything wrong regarding the driveshaft balance as the rumble problem was there before they touched it, but the shop that did the subframe reinforcement might have forgot to mark them.

[M3TA5IN]

I would like to take a ride with you and pin point where the vibration is coming from.

E46 M3 SMGs are known to have a "shudder" or vibration and a clutch replacement normally fixes this, BUT I don't think this is your problem because you are getting it at high RPMs under hard acceleration. So this makes me think that possible you need to replace some more bushings. Specifically the center support bushings. Your driveshaft can flex and these cars are so tight together the vibration could be your driveshaft slightly rubbing when it flexes.

Chances are it could be doing it in a larger range too you just can't notice it because of the plethora of useless sound deading material that is on these cars.

When I ripped out all the interior on the M3 and went for a drive I discovered all kind of problems/sounds I had no idea about before because I couldn't hear them.

I don't think it is a wheel, that is very noticeable the faster you go and I think you're a pretty smart dude and would know this.

Edit: don't mind me, still asleep. Didnt put CSB and center support bushing together lol


Sent from my fancy city machine.

[UdubBadger]

might not be wheel but possibly rotor warping? the diff in these cars is super weird, I get a clicking sometimes when I hit it hard going into 2nd or 3rd in my 6MT. It could be normal but maybe not.

[LivesNearCostco]

The driveshaft has splines that line up. Mine has somewhere between 16 and 24 splines, giving 16-24 assembly options. The M3 driveshaft is different but is probably also splined. If you are lucky, the driveshaft was already marked or the first shop to take it apart marked it to show how it goes back together. There are shops that can test and rebalance your driveshaft, but you have to take it off and send it to them. If the U-joint is bad, it can be replaced but not sure how to tell if a U-joint is bad.

I don't know if an unbalanced driveshaft could cause as much thumping as you're talking about. I wonder if there is chance the shop made an installation mistake and the new CSB has failed already? But only way to tell is to drop the heat shield. On my car that requires dropping the exhaust--not sure if exhaust has to come off on the M3.

I had read that drive shaft unbalancing or bad U-joints could maybe cause something like this. This may be a dumb question but I've never taken the drive shaft apart on this car, is it a finite amount of configurations (like two) that the drive shaft can be re-assembled in or is it infinite configurations? Namely, would there be any chance of re-assembling it right, or if there were no marks made to track the "balanced" configuration am i just shooting in the dark?

I doubt the shop that did the CSB/Guibo did anything wrong regarding the driveshaft balance as the rumble problem was there before they touched it, but the shop that did the subframe reinforcement might have forgot to mark them.

[kakashi169]

I had this happen to me before too and it turned out to be a bad ignition coil and spark plugs. Check those.

[M3TA5IN]

The driveshaft has splines that line up. Mine has somewhere between 16 and 24 splines, giving 16-24 assembly options. The M3 driveshaft is different but is probably also splined. If you are lucky, the driveshaft was already marked or the first shop to take it apart marked it to show how it goes back together. There are shops that can test and rebalance your driveshaft, but you have to take it off and send it to them. If the U-joint is bad, it can be replaced but not sure how to tell if a U-joint is bad.

I don't know if an unbalanced driveshaft could cause as much thumping as you're talking about. I wonder if there is chance the shop made an installation mistake and the new CSB has failed already? But only way to tell is to drop the heat shield. On my car that requires dropping the exhaust--not sure if exhaust has to come off on the M3.

There are actually multiple assembly options. I just looked at the e46 M3 driveshaft and it has a CV joint which I didn't know that.

However, these assembly options would only be the case if the DS was completely taken apart. In reality as a whole drive shaft there should only be 1 or 2 options. BMWs use a flange set up and looks like the bolt pattern will only go one way.

It is rare that u joints do go bad but it is possible. I don't know if BMWs have grease points on them either.

An out of balance driveshaft is extremely noticeable though. I would actually expect him to have more vibration than he is if this was the case.

The CV joint could be wore out as well and binding causing the vibration.

Disclaimer: this is all coming from my driveline knowledge in jeeps. I've never actually worked on a BMW driveline.


Sent from my fancy city machine.

[DSC-off]

A shop I took it to last week noticed that the transmission was somewhat loose, they said that they could move it about an inch. They are going to put some new transmission mounts in tomorrow (hopefully without taking the whole car apart).

I also found some NGK oem plugs on amazon for what appeared to be a reasonable price so I'm going to throw those in for good measure as well (at least 30,000 miles on the current plugs, probably more). If a coil pack was bad (or going bad) the car would be throwing a cylinder misfire code wouldn't it?

[Torxuvin]

When did you have your last valve adjustment? I had a buddy whose M3 was way off. I think he had to use 19 shims or something absurd to fix it. It had a shutter around 3-4k under acceleration. Completely gone now. Gained a lot of power back.

I suppose it could be an smg thing. I'm much more familiar with the 6spds.