Vibration noise - PeachParts Mercedes-Benz Forum

firstdiesel · #1 09-21-2012, 09:30 PM

Guys, I know this is like chasing a greased pig blindfolded, but I have a vibration noise which seems to be located at the transmission tunnel right behind the front seats. It does it in gear and in park equally and it gets louder with higher RPMs. It is somehow engine to frame related and it doesn't matter if you are moving or not.

Secondly it changes pitch, or disappears, when the ride changes. For instance, driving down the highway 65 mph and you go over a bridge the bump will cause it to be quieter for the 1 second while the weight lifts. Sounds strange I know, but any ideas?

firstdiesel · #2 09-22-2012, 12:37 PM

The transmission mount doesn't "appear" to be collapsed or broken, but that doesn't mean it isn't I guess. I was wondering about the diff mount as well, but would that translate engine vibration through two rubber flex discs? I would think, and possibly incorrectly, that the rubber flex discs would damper engine vibration.

SD Blue · #3 09-22-2012, 11:33 PM

If you are getting the noise whether moving or not, I would have trouble suspecting anything in the driveline. Maybe it is an exhaust problem, such as leaking flex pipe on the downpipe. This will show up as carbon tracks in the surrounding area.

Diesel911 · #4 09-23-2012, 01:01 AM

Inspection time.
Maybe the Transmission Cross Member that the Transmission Mount attaches to is loose.

Also the Motor and Transmission Mounts all work together. Maybe a Motor Mount is having an issue that the Transmission Mount is trying to take up the slack.

vstech · #5 09-23-2012, 09:04 AM

so many things it could be. start at the motor, since that's what's vibrating. inspect the motor mounts, and move back. don't forget the exhaust has a set of mounts that attach to the transmission bellhousing. if the diff mount is sagging, the entire subframe would be out of position, and it could easily cause noises...

Brian Carlton · #6 09-23-2012, 09:14 AM

Quote:

Originally Posted by firstdiesel

The transmission mount doesn't "appear" to be collapsed or broken, but that doesn't mean it isn't I guess. I was wondering about the diff mount as well, but would that translate engine vibration through two rubber flex discs? I would think, and possibly incorrectly, that the rubber flex discs would damper engine vibration.

When was the transmission mount last changed?

When were the flex discs last changed?

When was the center support for the driveshaft last changed?

When was the universal joint in the middle of the driveshaft last changed?

firstdiesel · #7 09-23-2012, 02:27 PM

Looks like a regular jack stand inspection is in my future. I don't have the answers for Brian but that was on my "to do" list within the next couple of weeks. Motor mounts, trans mount , flex discs, center support, diff mount, diff axle seals, pinion seal, axle boots. I'll start there and report back with a result.

Thanks everyone

rjz5400 · #8 10-17-2012, 12:28 AM

well?

firstdiesel · #9 10-17-2012, 11:19 AM

Starting the replacement of engine mount, transmission mount, both flex discs, center bearing, diff seals (axles and pinion), diff mount and switching the axles tomorrow afternoon. I have all the parts and some time to make it happen. The only thing that gets my blood pressure going is the center bearing. I don't have a press to put the bearing on. A three arm puller isn't tough to come by, but I don't have access to a press of any kind.

I will report back if it fixed the noise, and if it didn't then at least the rubber will be new. My only other thought is the rear sub-frame mounts and I don't even want do shell out the cash for those on a wagon.

Biodiesel300TD · #10 10-17-2012, 12:19 PM

Quote:

Originally Posted by firstdiesel

The only thing that gets my blood pressure going is the center bearing. I don't have a press to put the bearing on. A three arm puller isn't tough to come by, but I don't have access to a press of any kind.

When I pulled mine off, I just used a hammer and a oak dowel, and tapped one side then the other and slowly worked it off the shaft. Put the new one on the same way. Still going strong after 60k miles.

rjz5400 · #11 10-17-2012, 01:32 PM

sure, i pulled mine off by hand and used the old bearing to bump it down until it was fully seated. by hand of course no tools at all.

GLWR

86-300sdl · #12 10-17-2012, 01:34 PM

[QUOTE=Biodiesel300TD;3030688]When I pulled mine off, I just used a hammer and a oak dowel, and tapped one side then the other and slowly worked it off the shaft. Put the new one on the same way. Still going strong after 60k miles.[/QUOTE]

Same here.....No problems

firstdiesel · #13 10-22-2012, 08:39 PM

Okay, update time. I spent the weekend and replaced the differential axle seals, both flex discs, center bearing, rear diff mount,transmission mount and both motor mounts! I need to do this on separate weekends! Anyway, its my everyday driver and I can't afford to have it off the road long.

Both flex discs had cracking in them, so I am glad to have it changed. The center bearing rubber had pulled free from the bearing and the driver side motor mount had separated, but not like some of the pictures I've seen here. Either way needed to be changed.

Success? NO! The aforementioned vibration still exist!

Can rear sub-frame mounts on a wagon cause this kind of vibration? I really don't know where to look. The exhaust looks fine and not touching anything and the exhaust to transmission bracket is solid tight.

If I can hear it while its not moving and in Park, Neutral, Drive would you suggest putting a jack on the body + a piece of wood and lift up on the body near the mount to see if the sound changes?

Just scratching my head here. Advice needed.

Oh, and if you want to know how the center bearing removal went......http://www.peachparts.com/shopforum/diesel-discussion/327628-bearing-explosion.html