Trying to figure out a noise/vibration - E82 128i

So are the vibrations fairly well gone under 70mph? Does it annoy at street speeds or really only present at highway speeds? 

I would seriously consider having the wheels road force balanced at a facility with a hunter machine if its now a small amount of vibration present at highway speeds. Doesnt hurt, is cheap/fast, doesnt involve having to bolt/unbolt any other drivetrain parts, and may be a small contributor.

In reply to Olemiss540 :

It's fine at speeds below 50, and really minimal below 60 at this point. It's just on the highway that it's significant.

It's not impossible, but I seriously doubt this is a wheel balance issue. Something about the way the vibration emanates evenly through the whole chassis doesn't feel like any wheel balance issue I've had. It's also linear based on speed, rather than the "worst at Xmph, less above and below" feeling that wheel balance always seems to impart. I can always throw on the snow tires for testing if I run out of other options, but the last time I tried that there was zero difference (that's pre-new driveshaft, but the car has had very few miles since).

I would throw snow tires on it. Then if that doesnt help you can source a cheap diff on ebay for under 200 bucks and resell it if it doesn't help? Just some thoughts.

Put it up on the lift at my indy's shop this morning and ran it up. The remaining vibration seems to be coming from the diff, so it could well be the pinion bearing that several have suggested here. I've located a new diff locally and hope to have it by early next week (they have to pull it). Fingers crossed this finally brings this ridiculous odyssey to an end.

Changed the diff with a good used one with 50k fewer miles. It took all day and it nearly killed me, but I did it, on my back in the driveway. The test drive revealed no change in the vibration. I'm at a loss. I don't know what to do next, and I've thrown so much money at this already that I can't really throw any more.

Aahhhgggg.  What a disappointment!  I mean it's bad enough for me - I desperately wanted to hear that the car was finally restored to its former glory!

I know my dad fruitlessly chased a vibration on his old chevy van.  He systematically disconnected different things to try and isolate the issue.  
 

I don't recall - does it vibrate on the lift/jackstands?  If so, start taking things off/disconnecting them.  Wheels, axles driveshaft, even the tranny. 
 

Does the diff mount to a subframe?  Could be bad subframe bushings.  The can look great and be completely boogered..  And can be a bear to replace unfortunately.

This is driving me nuts from the sidelines, I get all excited when I see this thread bumped up, hoping you've found the culprit.

if I were in your shoes I'd take it to Rogue Engineering in NJ to see if they can figure it out. They seem pretty engineering heavy and good at troubleshooting, and do a lot on BMWs.

Diff is mounted to a subframe. I've got poly inserts in the subframe bushings, but the bushings looked absolutely solid when I put the inserts in a couple years ago. Also, there's no change when you go power on or off, which I would think would be an obvious sign of those bushings going bad.

We checked it on the lift at my indy's shop last week. The vibration we felt was clearly centered on the diff, and less apparent the further you got from it. If it's not the diff, then all I can think is that the new driveshaft may be out of balance at the diff end. That's where the only weights are, but that doesn't really mean anything.

At this point I'd love to throw it at a shop - any shop - and tell them to fix it until it's fixed, but the money to do that was spent on previous attempts to solve the problem. It's going to be a one-man show for a while now.

The replacement for the replacement driveshaft has arrived. Planning to swap this weekend. Cross whatever digits you have available.

In reply to 02Pilot :

I'd remove the poly inserts and try it again.  The driveshaft might be within tolerance, but the tolerance was allowed for NVH-wise by compliant bushings.

In reply to Pete. (l33t FS) :

I guarantee those inserts are not the issue. They're only in the subframe-to-body bushings; the diff mounts are still rubber. The only thing they really do is control the lateral movement of the subframe. The car was fine for years with those inserts in place before this problem appeared.

In reply to 02Pilot :

Fair enough, but I've long noted that difficult diagnoses always end up being something that one knew was not a problem, so it was ignored while chasing other things.

Also, poly anything where the OE had rubber, especially rubber with voids, is amazing at transmitting vibrations and resonances that one wouldn't think would be possible.

i had a car with a cyclic rumble at Interstate speeds that you could feel through the floor.  It was rear control arm bushings.  The OE bushings were tuned to not transmit that noise.  It was only apparent after replacing the driveshaft, was fine before that.  He must have had a good initial driveshaft while the replacement was closer to the edge of production tolerance.

I'm in the pull the poly subframe bushings camp and see what happens, are they really adding that much to the enjoyment of the car at this point? 

I'd still try to find another set of wheels as well just to cross that off the list even if it doesn't seem logical with the rest of your troubleshooting, it's just so easy to do (does your indy mechanic have a set kicking around to do a quick test with? Snow tires although they might just cover up the sound?). 

In reply to Pete. (l33t FS) :

It's a fair point, though I'm still skeptical that the inserts are the issue. My 2002 has full poly diff bushings, and in that car I wouldn't be at all surprised if they contributed to a vibration, but the subframe bushings in the 128i are still primarily rubber.

That said, if the new new driveshaft doesn't solve it, there's a good chance I'll either pull the inserts or light the car on fire and walk away.

In reply to adam525i :

I did run it with my snows a while back - no change. They're quieter than my summer tires, so I don't think they're masking anything. As for the inserts, yes, they are worth it. Without them the rear end feels like it's on a six second delay when you turn in. I can't imagine pulling them out permanently.

I still think you could swap the Diff in 3.4 minutes while the driveshaft is out. For the cost of a used diff for these things being so cheap, I dont see why its not worth a final salvo.

In reply to Olemiss540 :

I did - I got a unit with 50k fewer miles from a local yard. It made no difference.

Dumb idea.  Take off every piece of belly plastic.

I had been chasing a 50 mph-and-up hum for weeks on an A2 Jetta.  One day my buddy was passing me on the highway when he was going with me to drop the car off and give me a ride.  He didn't know why I was taking it to the shop.

When we got to the shop he said "how can you stand that noise?"  He noticed that a plastic belly pan was buzzing in the wind.  Ripped it off, noise gone.

I know it's a long shot and probably not the issue, but like Spock says...  If you eliminate the impossible, whatever remains, however improbable, must be the truth

In the unlikely even that pulling the inserts from those POS subframe bushings BMW so disappointingly used actually improves the noise, I think that would just be a pointer that the true culprit is something loose on the chassis side being excited by some frequency making its way into the subframe, and not that the inserts themselves are the problem.

Some of the undertray pieces will be off when I swap the driveshafts, and the others are easy enough to pull. That said, since I've had them all off quite recently, I can state categorically that they are all intact, with all fasteners present. It's possible one of them is vibrating, but nothing is even close to loose enough to flap around. Further, since the vibration is present with the car stationary, it would have to be a vibration caused by something else, rather than the undertray moving in the airstream.

The subframe bushings inserts may be slightly amplifying the way the vibration is transmitted to the unibody, but I tend to agree that they are a secondary factor at most.

At this point, I'd be tempted to swap the drivetrain into a different chassis, say a 2002.  If the vibration goes away, roll the E82 off a cliff and be done with it.  Frustrating to say the least.

JoeTR6 said:

At this point, I'd be tempted to swap the drivetrain into a different chassis, say a TR6. 

FTFY.

Driven5 said:

JoeTR6 said:

At this point, I'd be tempted to swap the drivetrain into a different chassis, say a TR6. 

FTFY.

Then he'd just be trading vibration for rattles.  But that would be fun.