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

In reply to adam525i (Forum Supporter) :

I agree. Its going to be a pain as there is probably a heatshield covering the driveshaft. I would give the center support bearing a good check. 

Those symptoms sure seem like driveline.  I'd pull the drive shaft so you can actually feel the center support bearing and whatever that has for a joint in the rear.  U-joints, bearings and CV joints can get notchy and noisy without being loose so you really can't test them in place.

Took it to my indy and we put it on the lift and ran it. The vibration is still present, but not as strong without the interaction with the road. He seems inclined to think it may be internal to the transmission, or possibly the clutch or flywheel, though he didn't hear anything definitive with a stethoscope. Nothing is visibly shaking, nor are there any signs of anything rubbing. I fear this means I'm going to have to start throwing parts at it, or wait for it to blow up.

Updating this in frustration. The vibration was bad enough that I didn't want to drive the car any more than I needed to - not exactly an ideal characteristic in a daily driver - and since we couldn't pin it down beyond it being in the driveline, I loaded the parts cannon and had my indy replace basically every consumable from the clutch back to the diff: clutch, flywheel, all the accessible seals, center support bearing, guibo, exhaust mounts, and probably a few things I'm forgetting. While he was in there he saw that the reluctors on the halfshafts were rusted, so we got a set of clean used OE replacements. Aside from the halfshafts, the only thing he found was that one of the U-joints was binding. He lubed it and got it moving freely again. Other than that, nothing was even close to needing to be replaced or showed any problems.

The result of all this was that the worst of the vibration, which as getting rather violent, was gone - great. Unfortunately, what was left was a higher frequency vibration, only from 45mph+, and again throttle position dependent; at highway speeds and constant throttle it's barely evident, but on or off throttle at 45-60mph it's more pronounced. There's a booming resonance associated with it. If I had to guess I'd say it sounds like a bearing grinding itself up. I can feel it through the chassis and the gear lever, but not the steering wheel. Having replaced so much, all that's left that fits the profile is the output shaft bearing, the U-joints, and the bearings in the diff. It's not affected by turning, so I don't think it's a wheel bearing (plus it sounds like it's coming from under the car).

So, a couple follow-up questions. I strongly suspect the current issue is the result of the same failing component - naturally, the binding U-joint seems the most likely culprit. First off, does anyone have experience with a U-joint acting like this? I certainly don't. Second, any best guesses as to which of the sources mentioned above might be the most likely culprit? Third, have I missed any possible suspects?

Pinion bearing in the diff if it's making a roaring sound is my initial guess.

But that opinion is worth what you paid for it.

It seems to me that the binding U joint would impart a lot of unusual loads (and wear) primarily directed into the bearing immediately adjacent to it.  That's where I'd start.

I hadn't considered that the U-joint might have stressed the adjacent bearing. Right now my thinking is to drop the rear end of the driveshaft to check that 1) the U-joints are still moving freely, and 2) to see if I can detect any issues with the diff (when my indy initially investigated this he didn't detect anything wrong with it). I might need to drop the halfshafts off the diff to get a better feel for what it's doing, but my concern is that I even if I don't feel anything in the diff while it's static, there may well be a problem at speed. Somehow I fear I may have to throw a used diff in this thing just to rule it in or out. 

OK, more frustrating updates. Just got home from the shop. Long story short, we decided that the driveshaft was the likely culprit after finding the rear U-joint bound up in one axis. New aftermarket driveshaft was sourced and ordered (BMW doesn't have replaceable U-joints on the factory part, naturally). It was installed this morning. The test drive and drive home revealed that there is still a vibration, but it has changed. It seems - pending further driving for more data points - that now the vibration simply increases with speed, whereas before it came in at around 45mph and faded away around 70mph. It is a similar vibration, felt through the unibody, but now seems more regular; with the old driveshaft there seemed to be a little variability and oscillation to it.

I'm thinking the replacement driveshaft may be out of balance, but I've lost all objectivity and good sense about this problem at this point, so I figured getting a few more thoughts on the problem would be a good idea.

I'm with Driven5 on this. That binding u-joint may have berkeleyed the pinion bearing.

In reply to AngryCorvair (Forum Supporter) :

My understanding (and it's only academic, not experiential) is that pinion bearings make noise when decelerating. I can't find anything that suggests they will make noise at 45+ all the time, nor do I find anything that talks about them causing a vibration. Not saying it's impossible, but what I'm experiencing doesn't seem to fit the textbook definition.

After lying awake most of last night trying to figure this out, I wonder if the replacement driveshaft was not set for precise length when shipped. We didn't check it before it went into the car, and I'm wondering if it's too long and pushing it out of line in the center. Shouldn't be too hard to spot running up on the lift.

How are the engine mounts?

Can you put it in gear while the rear end is in the air and see if you can locate now that the vibration is from lower speeds as well? Where did you source this new driveshaft? Diff swap is so easy I would locate a used diff and then resell it if that is not the cause. 

Guessing rear wheel bearing or rear wheel balance? Have you tried swapping the rear wheels to the front to see if it pushes the vibration to the steering wheel? Does the vibration go away when you hit the brakes?

Engine mounts are solid.

I'd like to get in on a lift to run it and inspect, but it's a week from Friday (Friday the 13th, naturally) before my indy can get me in. The current vibration is up through the chassis, and is completely unaffected by throttle position, brakes, turning, etc. It's just there, 100% correlated to vehicle speed. I'm thinking if I can get the car up in on stands in the driveway this weekend I'll do my inspection.

Edit: Staggered wheels setup, so no swapping F<->R, but way back when I put on a completely different set of wheels and tires, and nothing changed.

(didn't read far enough, deleted my comment...)

In reply to OldGray320i :

It's new. Every consumable is new, from pilot bearing to rear hubs. The only things I haven't replaced are the transmission and the diff.

In reply to 02Pilot :

 Yep, read further and realized I'm an idiot, deleted my comment, and hope nobody else saw it. 

Not that everybody doesn't know I'm an idiot, but, please, allow me to fool myself.  It keeps me happy.  

Solid in the sense that they are good, or solid in the sense that they are solid mounts?

Engine or diff torquing up under load usually results in weird transient vibrations like this.

It's super, super rare on a rear wheel drive for a CV joint to cause a shudder/vibration, but it's in the realm of possibility.  Did you have an alignment done right before the vibration occurred?  Changing the axle plunge by changing rear toe or camber can cause weird things as you ask the plunging joint to plunge in and out of its worn areas.

In reply to Pete. (l33t FS) :

Sorry for the ambiguity - solid in the sense that they are good. OE mounts, checked with a big prybar. Trans mounts are new (replaced when the trans was out for the clutch, not because they were bad).

I would not describe this as a transient vibration at this point; it's directly related to road speed and nothing else, consistent and repeatable. Alignment was done maybe two years ago, long before the problem appeared. All control arms (including bushings and ball joints) were replaced, along with struts/shocks, immediately prior to that alignment. All OE suspension parts except for Koni dampers.

Has the wheel balance been checked recently?  And could one of them have a bend in it. I saw this thread bumped and was hoping to see the "new driveshaft fixed it" update.

In reply to dj06482 (Forum Supporter) :

No one was hoping for "new driveshaft fixed it" more than me. I seriously doubt it's wheel balance. This feels quite different.

02Pilot said:

In reply to dj06482 (Forum Supporter) :

No one was hoping for "new driveshaft fixed it" more than me. I seriously doubt it's wheel balance. This feels quite different.

The only reason I offer that is that on my E36 I had a vibration that went away after I changed wheels. I know you had ruled that out in your earlier troubleshooting, but wondered if a wheel had become bent or had thrown a wheel weight in the interim.

Quick follow-on question for the BMW people. I couldn't leave well enough alone until next Friday, so I ripped the car apart in the driveway. The only suspect thing I found was that the center support bearing did not appear to have been preloaded. I could see the witness marks from the original clearly a few millimeters forward of the new bearing mount. I can't find anything in Bentley or the TIS regarding preloading, but every CSB I've dealt with on a BMW requires it. Anyone have a quick yea or nay on preloading on the E8x/E9x chassis?

I sure would. I think it was 4 or 5mm preload towards the front of the car. 

In reply to Olemiss540 :

That was my instinct too, so I did just that. Test drive shows it's better, but there's still some vibration as speeds climb past 70. I think the next thing is going to be to undo the bolts on the guibo and rotate the flange one hole (there's only three, so that's still 120deg) and see what happens.