REPOST W/CORRECTIONS: Transmission Mounting Bracket Removal Question

[EricSilver]

I did some bad cutting and pasting in the previous iteration of this and parts of it made no sense. So here is the correct version.

Regarding this photo from a PelicanParts W211 Transmission mount DIY:



1.) Is removing the two nuts (green arrows) necessary to drop the mounting bracket? They don't seem to be attached to the bracket.

2.) What does the bolt at the red arrow do -- or what is it attached to? Mine is rusted to its backing nut and both spin freely, in unison. I can wiggle the bracket side to side a bit but it will not come off. I could feel the top of it when I maneuvered my fingers up the and turned from below; but it seems the same length as those other 6 that were successfully removed.

This was a show stopper for me and what should have been a simple repair was screwed up by... a screw.

I am doing this replacement due to some some strong vibrations in Drive and Reverse, with foot on brake. Car is dead quiet in Neutral but curiously vibrates a little in Park. In park, if I put my hand on the engine cover, I can can also really feel strong vibrations.

These vibrations were present for some time but became stronger after having my axles replaced last Friday so I am guessing transmission movement during the repair impacted the trans mount.

**I replaced the engine mounts today with new Lemfoerders, so they are not the cause.***
(Engine mounts are shockingly easy to do on this car; took me longer to remove/reattach the belly pans than it did to swap out the mounts, so why are shops quoting 6+ hours and $1200+ for this job? Hmm.....)

[EricSilver]

OK, I see my error:

Those nuts have to come out since the black-ish backing they are attached to is indeed part of the bracket, as shown below, and which I overlooked when I skimmed through the DIY. The spinning bolt is not attached to anything (at least not anymore) and therefore is not the cause of my removal problem.

[URO Parts Support]

Pelican Technical Article: Transmission Mount Replacing
https://www.pelicanparts.com/techarticles/Mercedes-W211/109-TRANS-Transmission_Mount_Replacing/109-TRANS-Transmission_Mount_Replacing.htm

Looks like the captured nut for the red bolt is inside a small formed steel hanger (top center of below photo), and the bolt needs to come out so you can remove the crossmember from the body and trans mount bracket. If the nut spins, maybe you can jam something between the nut and the side of the hanger to hold it in place well enough to loosen the bolt.

[EricSilver]

That was pretty much the issue -- though I did not see it myself.

Common sense prevailed and rather than spend any more time under the car in hundred-degree heat, I took it to the mechanic's to have them free the bolt, and then just insert the new mount while they were at it. Had that bolt not been a show-stopper, I would have completed the trans mount and engine mounts in about an hour. It's incredible that shops estimate 8 or more hours to do the same.

I am surprised at how important engine/transmission geometry is to the car's proper performance. The old mount had collapsed; the new one raised the transmission by an inch or two, and the change in vehicle performance was remarkable.

Throttle response is significantly improved: Depress the accelerator and the car takes off, with none of the slight lag I noticed in the past year or so. Passing on the highway is effortless. In Sport Mode, 1st to 2nd gear upshifts on hard acceleration from standing starts happen by 4500rpm vs the previous 6000rpm. Average fuel economy in mixed city/highway driving is back to 22-23mpg, after falling to 18-19mpg. Ride feels smoother. And transmission-related vibration is gone.

Another vibration reduction came after an oil change yesterday. I typically use LiquiMoly 2332 5W40 but forgot to order it, so picked up some Mobil One 0W40. There is a noticeable difference in the car's sound and feel -- not profound but noticeably smoother and quieter, due to the lighter oil.

Another source of vibration will hang around for a while: New axles. Apparently there is a breaking-in period during which vibrations will be felt in Park; Drive (when stopped at a light); Reverse; and on acceleration from stop. Mechanic says to give it 2000 to 3000 miles to work itself out.

A week and a half ago, when I had the axles installed, the vibrations were very strong, especially on acceleration from stop; Reverse (with brakes on); and Drive (with brakes on). They were nonexistent in Neutral or when the car is moving. Since then, I have noticed a significant reduction in vibration so I believe the mechanic is correct, and all vibrations should be gone soon enough.

I have read posts by people who installed new axles, felt the vibrations, then went back to their old ones (with reboots) because of that. What they should have done, however, is patiently ride out the break-in period -- after all, putting new axles into an old(er) car with different material tolerances will not yield perfect results until the new parts start to wear a bit. (And my experience with the trans mounts demonstrates how critical small tolerances are in this car.)

Finally, the last vibration source (when the car is moving) is my front tires -- Yokohamas get "thumpy" as they age and I won't have optimal smoothness until they are replaced.

Originally Posted by URO Parts Support

Looks like the captured nut for the red bolt is inside a small formed steel hanger (top center of below photo), and the bolt needs to come out so you can remove the crossmember from the body and trans mount bracket. If the nut spins, maybe you can jam something between the nut and the side of the hanger to hold it in place well enough to loosen the bolt.