how much play in the drivetrain?

[cookbw]

I've pulled out my driveshaft to replace the center support bearing... hoping to fix a coarse vibration that only occurs under hard acceleration in 1st or 2nd gears. The vibration feels like it's coming from about the location where the center bearing is mounted. There is no vibration at high speeds, just hard acceleration. While under the car, I noticed a couple other things that concern me.

1) Vertical/lateral play in the driveshaft (tranny-to-differential). By grabbing the driveshaft near the center support and tugging on it, I was able to move it side to side about 1/2". That seems like too much to me, but I'm not sure. Looking at the driveshaft/center bearing before I removed them, the rubber in the center bearing is compressed more on the bottom than on top, like it's bearing some weight (see pic below).

2) Rotational play at the differential. With the car sitting on ramps (rear wheels fixed) I can rotate input flange of the differential with my hand about 5mm back and forth and I hear clanking from one side to the other. Does anyone know much play is normal for the diff?

3) The final driveshaft (differential-to-rear wheel) on the driver side is easily moved laterally along its axis of rotation about 1/2 to 3/4" by hand. Passenger side doesn't move much at all. The rubber bellow on driver side is ripped, so I probably need to pull this off and replace anyhow.

As always, helpful tips/feedback are truly appreciated. Thanks!

 

[hans3]

I'm unable to view your pics because of my firewall but based upon your descriptions...

The play and clanking you reference in points 1-3 are observable in other cars and not necessarily the source of your coarse vibration. Specs exist for the amount of differential free play, but such free play will not cause your vibration.

The torn CV boot will have greatly shortened the life of the CV joint; a shot CV joint will cause vibration under acceleration, but it can usually be traced to that corner of the car. In contrast, a driveshaft vibration will be perceptible as emanating from underneath the vehicle.

Is this vibration a new symptom or something the car has always had? If it's the latter then there are a number of other things that may be causing it. First off, you were prudent to carefully inspect the center bearing support. If the rubber carrier is torn in any way, then this would be the causal factor. If not then one should check the driveshaft's rotational runout.

The easiest way to do this is to reinstall the driveshaft and tighten the guibo nuts until there's a very small gap between the trans output flange and guibo. Rotate the driveshaft with a light shinning through the guibo gap (preferably from above). If changes in the gap are observed then the driveshaft rotation may not be "in plane"; it will waver. Causes of this can be very old / worn engine mounts, trans mount, or diff mount. You may have to throw some money at this thing in order to eliminate these as potential problem items.

 

[Bill Riblett]

Driveshaft vibration

Another likely problem is the u-joint on the rear of the driveshaft. On BMWs these are 'sealed-for-life' and are not easily replaceable. Eventually the grease in the bearings in the u-joints dries up and the bearings gall. Then the joint no longer moves smoothly and the bearings bind.

The practical solution is to send your driveshaft to someone familiar with BMW driveshafts, like Driveline Service of Portland
http://www.driveshafts.com/bmw
who will cut out the old u-joint and weld in a new one which comes with a grease fitting.

You can test your driveshaft if you remove it and move the joint through it's 2 planes of movement. If it does not move smoothly, it is bad.

 

[cookbw]

don't buy the Febi/Bilstein center mount for driveshaft

FWIW...I bought two replacement driveshaft center mounts for my car. first, a bilstein unit... then when i saw how soft and wobbly the rubber cushion was and was already flaking off, i bought the OEM unit. the OEM is seriously MUCH higher quality. it also costs 4X more, but it is so much stronger & better.

BTW...Thanks for your tips on the vibration issue! I've checked the driveshaft and its ujoints and splines are in great shape. It was recently rebuilt from Atlanta Driveline Service before I bought it. The trans and motor mounts look new, but the rear diff mount is really crusty. I've yet to check the driveshaft "rotational runout", but will definitely do that once I get back to reassembling things.