View Full Version : Spinning up a transmission on the bench

03-11-2009, 09:56 PM
Anyone have any ideas on how to do this? I just swapped out my transmission for a used one because I was getting a horrible driveline whining noise, but I now suspect it might have been the driveshaft center bearing. I suspected it was the transmission because I accidentally ran it low on oil after installing the output shaft seal wrong, but when I pulled the fill plug the fluid looked alright and there wasn't much on the magnet (some metal dust, but not much).

I'm wondering if there's a way to spin up the transmission without making so much noise that I wouldn't be able to hear the transmission. I tried using an air drill w/ a paper buffer on the input shaft (the only drill I have that will fit on the pilot diameter) but it was too loud. Tried throwing an old clutch plate on there and spinning it using a rod through one of the holes but I couldn't get it going fast enough.

I'm trying to decide whether I should pull it apart and check all the bearings, but I'd rather not if I don't need to.

Anyone have any ideas?


03-12-2009, 06:45 AM
I dont want to sound like a wiseass, but....Unless its REALLY hard to get to, wouldnt it be easier to have a look at the driveshaft bearing first?

In my years of fixing (non bmw) driveline noise, Ive only ever seen 1 or 2 noisey trannys, as opposed to thousands of hanger bearings and rear ends.

You can usually feel a bad bearing by just turning it, with your hand on it.

03-12-2009, 08:19 AM
Totally agree - I am 95% sure the center bearing is shot and I have already ordered a replacement. I'm just trying to figure out if there's an easy way to tell whether the trans was going as well (worried because I ran it a bit low on oil by accident).

03-12-2009, 01:56 PM
Manual transmission? Most common source of noise is input shaft bearing.

03-12-2009, 10:25 PM
Yeah... the input shaft bearing looks okay as far as I can tell, but it's hard to know.