FYI -I have a 91 940T.


I just replaced the motor mount and the tranny mount yesterday. After getting them all on I started it up and drove it around, now it has a droning vibration when in drive that was not present before. I don't suspect the parts, they are legit ones from FCP Groton.

I'm guessing that it has to do with the tranny mount. The FAQ is pretty short on instructions, it basically says "take off the old one, put in the new one". When I put the new mount in, I tightened the securing nut pretty hard. My thought is that I may be compressing the rubber mount too much, and keeping it from deadening the vibrations.

I'm planning on loosening the nut when I get back to the car on Wed, and see if it helps. I'm hoping somebody has gone through this before so I can avoid the trial and error of trying to make the vibration go away. Worst case, I'll just put the old mount back in and see if that fixes it.

Thanks,
Mike

Hi,
It is possible to install the tranny mount upside down and get what you describe.
How do I know ? Don't ask me.
Regards,
John H from Downunder

Had to laugh when I read this, it was really late Sunday night when I put on the tranny mount. I'll check that, it'd be a relief if I just had to flip it over.

Thanks,
Mike

I don't think the rubber is compressed when you tighten, he rubber is bonded to the metal parts of the mount and the bolts/nuts only tighten down on metal.
With the new mount the transmnission is probably sitting a bit higher and therefore at a different angle to the drive shaft and thereby revealing a previously quiet worn rear transmission output shaft bushing. Check for play at the tranny output. When worn it will give the sound you describe.

Thanks for the reply,

If I just put the old transmission mount back in, should this solve the problem? I would eventually want to fix this, but I do not have a free weekend for a few weeks and I liked to get rid of the vibration for the time being.

Assuming I can't eliminate the droning by putting the old mount back in, How bad is this for the car? Do I need to be worried that I am causing permanent damage? Or will driving it just continue to wear on the output shaft bushing/seal - which I will be replacing anyway?

Thanks,
Mike

D Hunter, I owe you one. It turns out I did have it on upside down, maybe the orientation should be added to the FAQ for boneheads such as myself.

Got it on right and the droning is gone, there is still some vibration coming from the exhaust but this is a far smaller problem.

Thanks,
Mike

I also have something that might be described as a droning noise. Does the car have to be moving to make this noise? Mine makes a noise at about 3000rpm, if moving or not.

Thanks,
Steve

A droning noise on the output of the transmission will only be present when moving. If it happens when stationary then it almost certainly is engine related. Describe the noise. Can you hear the noise while observing under the hood? Where does it sound its is coming from?

Thank you.

The noise can definately be heard from under the hood. Almost exactly 3000rpm. The exhaust shields are tight, so I don't think that is the cause. It does sound like a very loud loose exhaust shield. I can't figure where the noise is comming from - seems like the whole engine. The dash vibrates and there is quite a buzz in the cabin at 3000rpm. (The center console buzzes with the vibration.) After replacing the transmission mount, the vibration changed. It used to be occur from 2000-3000rpm, but was somewhat less pronounced. Now it is pretty quiet below 2800rpm, very loud at 3000rpm, and goes away above 3200rpm. I also changed the distributor at the same time - so I don't scientifically know that it was the transmission mount that caused this change or if it could be the distributor.

I am wondering if it can be the motor mounts. The ones in there are not compressed, but they do have small cracks on the surface - perhaps the previous owner used an inferior brand. However, at idle, there is no vibration. Are there other possible causes?

Thanks so much,
Steve