Driveline vibe sometimes 1984 300D - PeachParts Mercedes-Benz Forum

roundout · #1 02-13-2011, 09:35 AM

Hi all, I have a bit of a head scratcher here. MY 84 300D has a slight vibration at some times under certain conditions. This vibe seems to occur at highway speeds after a few minutes of driving when either coasting (down a hill, or if traffic is slowing up ahead) or when reducing the throttle. It sounds like it's coming from up front but I can't tell. The sound is worse than the vibration, kind of a rhythmic thumping. If you get back in to the throttle, the noise goes away. I am wondering if it's a wheel bearing, since being loaded or unloaded seems to make a difference.

I would suspect a driveshaft problem but in the past 24 months I've replaced the prop shaft itself (driveshafts.com), the flex disks, trans mount, both engine mounts, diff mount, and CV axles. I have newish tires and have had the wheels balanced and rotated several times. The noise and vibe are unchanged. I am wondering if maybe I installed a flex disk backwards or something? All the bolts and nuts are tight. So is the big nut on the prop shaft. With other cars I've had CV axles give me vibe and noise when loaded vs unloaded, so I was hoping that they would cure what ails my car but they did not.

I am beginning to get stumped. Whenever I get up under the car and inspect various components, the suspension is very tight. The PO had the entire front end rebuilt a couple years back. It drives fine. I am thinking of getting my grease gun back from my buddy and greasing the zerk on the new driveshaft - they said to service it at 25k miles and it's been about that many.

Any help would be appreciated.

vstech · #2 02-13-2011, 10:23 AM

passenger's side motor mount.
the driver's side can cause similar problems too.

roundout · #3 02-13-2011, 04:42 PM

Both motor mounts are a year old. I checked the bolts and they're all tight. I lubed the driveshaft but haven't driven yet. It did take a LOT of grease to get it to start seeping out. Maybe that will help.

roundout · #4 02-13-2011, 07:44 PM

I should add that this car has at least one dragging brake. I replaced the rubber lines and that didn't fix it. I haven't troubleshot the problem to find the culprit caliper(s). Back in the good ole Toyota-stuck-accelerator days I experimented with a rental Kia on a barren stretch of I-70 in Kansas seeing if I could overpower a floored accelerator with the brakes. After doing this twice, I noticed the brakes developing (among other things like fade, smell, and the like) a vibe, which I assume came from the rotors warping. Never buy a rent car. Anyway, I am wondering if maybe a dragging brake might cause a similar effect on this car. That would explain why it comes and goes and only comes at highway speeds. Doesn't explain why it changes with load or coast, though. Just thinking out loud.

vstech · #5 02-13-2011, 08:00 PM

my SD had a strong vibration when I got it going in 05, I traced the problem to a sticking caliper, changed it out, and the vibration went away. my theory is the heated rotor boiled the grease in the wheel bearings, and caused a vibration... no idea if this is what actually happened, but the vibration went away. I also changed the wheel bearings and races at the same time, so it could have just been a bad bearing that was close in tolerances ,but not perfect...

charmalu · #6 02-14-2011, 01:56 AM

Flex Plate the torque converter bolts to could be cracked.

Charlie

The Gears · #7 02-14-2011, 03:22 AM

Had the same problem, wasn't the flax plate but have a set of new bolts if required. I pulled the trani to check. The problem, two way to tight valves. Set the whole set and had a smooth running car. This simple fix after nearly replacing the whole dam car.

t walgamuth · #8 02-14-2011, 05:37 AM

Why did you replace the ds?

roundout · #9 02-14-2011, 09:50 AM

Quote:

Originally Posted by t walgamuth

Why did you replace the ds?

The U joint was dry and nearly seized and nobody here locally wanted to touch it. The drive when I picked it up was so bad you couldn't get above 50 without fear of the thing shaking itself to pieces. I knew it was the DS - I've had cars with bad U joints or bent/unbalanced DS before.

My car only had 1 owner its entire life before me and he was good on maintenance. Unfortunately, a few years before I bought it he got a E-CDI for himself and a G-CDI for his wife and retired the 300D. It sat for a few years doing nothing more than grocery store trips. I've had to replace nearly every piece of rubber on the car. Anything with grease in it, like the DS, is suspect, too. I knew this going in and my offer price reflected this fact.

Plus, back then, I had the money. Not so much anymore.

roundout · #10 02-14-2011, 09:52 AM

Quote:

Originally Posted by The Gears

Had the same problem, wasn't the flax plate but have a set of new bolts if required. I pulled the trani to check. The problem, two way to tight valves. Set the whole set and had a smooth running car. This simple fix after nearly replacing the whole dam car.

Valves set just before it got cold a few months back. The engine is super smooth, other than one injector nailing. It is something in the driveline.