2010 GL450 with 140k. Went to dealer for a few things I wasn’t going to tackle at home. I’ve noticed a strange vibration that comes and goes and had them diag it. They claim motor mounts and trans mount are broken. Anyone have any experiences similar. The vibration occurs around 70-80MPH on the interstate. It fades in for a while and then fades out. Noticeable enough to make headrests shimmy. I only notice going down interstate and not consistently. It does not change with speed or engine rpm (same speed, different gear, same vibration). I have not noticed any vibration at idle in gear stopped. A friend mentioned he thought it could be torque converter issue. It’s due for a transmission service but not sure where to go from here. Don’t want to doubt dealer but not sure what’s causing a vibration to come/go

 

Drive shaft.

 

Check the drive shaft flex disk for wear/cracks. If its not that, its more than likely a tire balance/pressure issue or the wheel/tire indexing to the hub assembly. Some times the heavy part of the wheel/tire assembly is matched to the heavy part of the rotor and it causes similar issues later down the road when the tire starts to show wear and the balance isn't as spot-on as it used to be.

 

so I’m not arguing, however wouldn’t things like wheels/tires/driveshaft change vibration with speed? Also would you think they’d be vibrations all the time? I’m baffled how at a constant 75mph how a vibration comes and goes

 

Anything that rotates not only has balance issues, but also harmonic issues. Thats what causes a vibration to come and go at certain speeds. Its very hard to pinpoint and aggravating.

 

This in only happening at a stop guys. Goes away as soon as i love. Car in drive and i have brake applied. If I put it in reverse same thing. In neutral it goes away completely. So what's activating on drive and reverse that would cause extreme vibration is my question

 

For you, it’s the transmission mounts.
For OP, drive shaft flex disc or tires out of balance.

 

Failed transmission mounts could lead to excess angle of the driveshaft flex, causing it to weaken and then develop funny resonance at various speeds.

If true, this would be another example of cascading issues.

 

The trans and engine mounts both just changed. Both were in good condition before changing as well. Im checking vacuum leak tomorrow to see if there is a leak somewhere that we are missing