The motor mounts were changed on the 300SE around six months ago, but there was not time to do the Transmission mount. It was obvious it would need doing from the condition of the motor mounts. In addition, I was feeling some vibration from the drivetrain at various times.
changing the W126 transmission mount is generally a simple affair. The transmission is jacked up a little, with care taken not to dent the pan. The mount is freed via three bolts – two on the crossmember with a 13mm socket and one to the tail of the transmission with a 19mm nut.
The old transmission mount was in poor shape. The mount had entirely collapsed and the rubber was doing very little. This was obvious when comparing to the new one.
The installation of the new mount was not straightforward. For some reason, I could not get the bolts into the mount through the crossmember. Sure enough, when I removed the mount, there were no threads in the holes! The new mount is an aftermarket one from Meyle. This was quite perplexing, but at 11pm I didn’t have the means to do anything about it. I don’t know if this is because there is a manufacturing defect; I have the wrong mount; or my car has been modified at some time. The old mount was so bad I did not want to re-install it. When I examined it to check the threads, it was clear that only some old grease was holding it together.
In the end I installed the new one using only the top mounting. This was enough to gently move the car out of the way so I could drive home in the 450SLC.
A couple of days later I purchased an M8 thread tap. This allowed me to re-use the bolts from before to install the mount. It would have been easier if I had access to a vice and the right tool to hold the tap instead of a pair of cheap vice grips. Once the thread was tapped the installation of the mount was as straightforward as it should be. The vibration is gone and you can feel the difference in driving the car. I’m not really sure if tapping some new threads into the Meyle W126 transmission mount was the right thing to do, but it did seem to be the best option at my disposal.
Next time I will try a different brand W126 transmission mount.
While I was there, I did an oil change on the car and installed a new breather hose. The old one was rock hard and they are not expensive. I had cracked one of the vacuum hoses installing a new air filter a few weeks ago, so I also installed a replacement vacuum hose. The vacuum hoses get brittle with age.
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