Help Confirming Source of Rear-End Vibration
 

Hi all.

My '97 ti (replacement for the 98 I drove for 10 years and totalled a couple of months ago) has developed a powerful rear-end vibration.

Details: 207,000 miles, Currently running 15" snow tires on steel rims, M-tech springs & sway bars, Bilstein shocks.
Brakes good. Replaced McPherson bearings last month. PO replaced R outer tie rod end.
In looking for this problem, I discovered that both of my inner tie rod ends are shot, but only barely (I'd checked them when I first got the car and there was no play, now there's barely perceptible play - lesson: always replace inner and outer together, like the PO did not do).
I have rotated both rear wheels with the pads pried back to reduce drag, and rear wheel bearings feel smooth and have no play that I can feel, fronts seem good, too.
I have had both rear wheels rebalanced, and have also swapped them with the fronts, all with no effect.
I've crawled all around under the car and the universals and CV joints look and feel good, and the axles and driveshaft do not appear bent.

The problem: A harsh vibration that feels like it's coming from the rear of the car (occasionally left, occasionally right, usually middle), that I can feel mostly in my butt, like a back massager gone haywire.
No vibration in the steering wheel.
No vibration in the gearshift (MT).
The vibration is affected by throttle position and road speed - it's worse at steady throttle, better with acceleration or deceleration, worst at about 40mph and again at about 70mph (can be bone-jarring when it's just right), and smooths out pretty well at about 80-85.
It is not affected by engine RPM.
There is no sound associated with it - no howling, growling, or grinding.
Taking sweeping turns in either direction does not change it.

These two threads, and a few other things I've read, lead me to suspect the U-joints / driveshaft:
http://www.318ti.org/forum/showthrea...ight=vibration
http://www.318ti.org/forum/showthrea...ight=vibration

I know that the U-joints are not worth trying to change, and that the driveshaft ain't cheap, so I'd like to have a pretty good idea of the problem before I throw parts at it.

Can anyone say anything definitive about this?

Thanks,

- Eric

This sounds like a classic flex disc/driveshaft issue. 207k is a lot of miles if neither of those have ever been replaced.

+1

Well, I feel better about my own diagnosis, then.

On my next day off, I'll have to get under there, disconnect the rear end of the driveshaft, and give it all a feel.
Then I can spend some money...

- Eric

Check out driveshaft specialists in texas if it is indeed the flex disc or u joint, theres at least a few of us on here who have gone with them and are plenty happy with the results.

Yeah, I've heard they're good. Looks like $378 with free shipping.
http://www.driveshaftspecialist.com/...0html/BMW.html

I've also heard that Wholesale Import Parts is good, at $367 with free shipping.
Has anyone heard anything about them?

With an $11 difference, I'll probably go with Driveshaft Specialist if nobody chimes in to rave about WIP.

Thanks,

- Eric

I got a replacement from Driveshaft Specialists about five years back- over 50K/mi on it with no issues so far. It even had pre-paid core return, IIRC.

Regarding the flex disc, I'll tell you from experience to use a BMW part only (not Febi, URO, MTC, etc.). There's a reason those other brands only cost a fraction of the BMW part. :cool:

Really? :eek:

There's a BIG price difference between the BMW and the "everyone else" parts.

Usually I get the part made by a reputable OEM, like Lemforder, and it's fine.

If I may ask, what brand did you initially buy, and what happened that made you shell out for the BMW part?

Has anyone else had the same experience?

I have not heard this for guibos for other German cars over the years, but I will take your advice seriously, as I put a lot of miles on the car, and I hate having annoying driveline malfunctions.

- Eric

Actually, Lemforder is one of the few aftermarket suppliers that I've used and have never had any issues with. Infact, they are an OEM supplier to BMW and MBZ (probably others as well). I'm not sure if Lemforder makes flex discs but if they do, I'd be comfortable using that.

When it comes to other brands, however, I won't skimp on critical or safety-related parts.

One time, in a pinch, I used an Üro flex disc because the BMW part was going to be special order and I needed to cinch the drive train up that weekend. The disc started developing small cracks after about 15-20K and after about 50-60K had completely disintegrated- like nothing except a few nylon cords remaining. If it weren't for the fact that I used OEM BMW hardware, that could have been catastrophic. (and I'm not especially hard on my vehicles).

Just ordered a driveshaft from Driveshaft Specialists and a Lemforder guibo (and some other stuff) from Pelican.

I plan to do the deed this weekend.

I'll post up how it goes, and will try to take a few pictures if anything goes differently from the way I think it should.

Hope it's not too $*#^ cold...

- Eric

i did this very same thing in december. when i pulled out the drive shaft you could see the bearing coming out of the u-joint.

only had 112k on it.

I successfully changed the driveshaft this weekend.

The car rides like a new car.

I have written up my experiences and advice here.

Thanks to all,

- Eric