i replaced my shot transmission mount on Saturday, it was completely disintegrated with the rubber detached from all points. Got a new factory mount installed, torqued to specs easy-peasy. However, now i notice a hum/whine in the cabin that sounds like it's coming from the drivetrain. The sound increases with speed/RPM and is most noticeable when coasting or coming to a stop.

When supporting the transmission for the mount swap i only lifted the trans 1 inch, and the trans pan was well supported with 2 stacked 8x11 plywood planks.

could i have damaged another component of the drivetrain in the process that might be causing this new noise? center support bearing? flex disc? im traveling out of town later this week so i can drop it off at my local indy but i wanted to know if anyone has some suggestions first.

anyone?

Have Engine Mounts and Pulsation Dampers been done already? Those noises all mask each other very well, especially if you feel it in the floor pan. If you feel it in the floor pan around 1800-2100 RPM, then I'd suspect Pulsation Damper first. Known issue at this age. Shouldn't be flex disc, which you can see with visual inspection. Search "Pulsation Damper".

maw

thanks for taking the time to respond Maw. I haven't dont the engine mounts yet, but they are sitting on my bench, i just didnt have time on saturday. I havent checked the pulsation damper, that s a good suggestion. i rebuilt the valve blocks and replaced the f/r accumulators and did CHF11 flush a few months ago.

i will say the the humming only occurs when traveling and subsides at rest which is what led me to drivetrain.

My dollar in a bet says that saggy engine mounts are every bit as poopy as the transmission mount was.

They don't live long. Year or two is the best I have got out of them before they spew the gooey goodness.

Pulsation damper is common. I did one in my car to quiet the pump down.

thanks JohnLane, the engine mounts are definitely shot, i have them just not the time to replace. Could the engine mounts cause the hum/buzz? it literally sounds like a honda revving while driving. it seems to be related to vehicle speed and not RPM, persists when coasting and shifting to neutral, so i'm perplexed. i'll drop it off at the shop later today, but any other thoughts/suggestions are appreciated!

If you're wearing some 6 year old Dunlops, it could be the tires... but I think we're just starting with the basics of what yields driveline hum and vibration in these cars, specifically. I would say wheel bearings, except they're not known to be issues on these, at least I've never heard of it. If the car was wearing 22's for 6 years before you got a hold of it, then maybe. You don't seem like the sh*tty tire on 22s guy, but I guess I'd have them check wheel bearings while they're in there. The thing is, wheel bearings and drive shaft flex disks are MUCH easier to diagnose once you've ruled out engine and trans mounts and dampers, is the basic advice you're seeing.

If a slow rev in neutral or park DOES NOT produce the issue you're after, then I'd move to flex discs and wheel bearings (rolling issues as opposed to stationary). Engine mounts and dampers will produce the hum and vibration in Park, dampers generally around 2k RPM, engine mounts anywhere under 3k, which is why they mask each other, leading mechanics to hunt and peck, throwing parts at it one step at a time when it's usually mounts AND dampers.

maw

^^^This.

On mine, the hum and floorpan vibration got me all mounts changed. That cut things in half, and I noticed the difference for sure. "Wow, mounts made a huge difference! But still there's that annoying noise at 2k rpm even when I'm not moving, that goes away once RPMs rise... what is that?" Pulsation Damper.

maw

thanks for all your inputs again. i took the car to my indy while i went to the mountains last week and they said that some sound insulation got knocked loose when changing the tranny mount. $178 later it's fixed and right as rain. Now to get to those engine mounts....

They are easy to do. *Cracks whip... Get to it!

You should loosen the transmission mount bolts on the bottom of the support bracket before you lift the engine to do the engine mounts. Otherwise you could tear the new tranny mount. I know, it’s undoing what you thought you already did, but you tear that tranny mount and you will be upset at yourself for having to replace it yet again.

...and by “loosen” I mean to say “remove”.

thanks GrepAwk, will do! not anxious to duplicate this work until needed from use!

Adjustable rear suspension can stop the un-even tire wear and help traction, handling and alignment. http://ultimatepd.com/amg-w211-e55-t...nsion-set.html