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Unbalanced drivetrain?
1 Attachment(s)
1984 MB 300d, 131k miles
To start with, here is what I have done in the past several months. Replaced the main motor mounts and shocks. (only one shock was still good). I then found that the transmission mount was very, very bad, and replaced it. I then started noticing that there was a medium frequency vibration in the 10-20 mph range. The vibration was there regardless of acceleration or deceleration, or throttle position. Further inspection showed that the drive shaft bearing support was detached (rubber ring blown). Due to time constraints, I let a local garage replace the bearing and support. The dynamics of the vib changed, but still present. So I loosened the transmission mount and bearing support bolts, drove around the block and tightened the bolts while the car remained on all four. A change in the vibration characteristics, but still there. I was not sure what I was seeing on the flex discs, so I just changed them out. The old ones were most likely ok. So now I still have a vibration. It is at its worse around 40mph, and goes into a thrumming around 60 and above. This is not a huge shake, more of a deep sound, but should not be there. There are still weights on the shaft, and no apparent clean spots where a weight might have fallen off. The included picture shows the indexing marks. Are they close enough ? What else? |
What kind of shape is that u-joint in?
Also what happens when you coast and have the car in neutral? Do you feel anything in the steering? Also, check for bent linkages rubbing on the body or firewall. |
You probably have a worn u-joint.
These vehicles don't see much angular deflection in the u-joint so it wears mostly in the center of it's throw. By removing the shaft and deflecting it at the u-joint, it will usually feel firm (no play) the further it's deflected away from center. I haven't found a rebuilder nearby and have had to rely on Thrash Driveline in San Antonio, TX to supply me with rebuilt units from somewhere in California. |
After a drive...
The vib is there at 45, with the transmission in neutral. Steering is smooth. I have had some front end work done, and they were good about looking around at the mechanicals up there.
Driveshaft removal does not sound like fun. Thanks. |
Put your front wheels on the back, backs on front. See if that changes the sound. I'm living with a similar problem, and I'm convinced its merely an out of round tire.
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answers
I will give the tire rotation a shot. Discount tire loves doing stuff like that, and a much cheaper possible solution then a new driveshaft.
Both flex discs are new Lemforder. The old ones, after close inspection, did not show the obvious signs of wear commonly mentioned in this forum. I will take a look at the included threads a little later, thanks for including them. |
Mercury,
I went through the same thing on my 84 500SEL. Same vibration. I read somewhere on this site (can't seem to find it now) that the BIG nut on the driveshaft has to be TIGHT. It's the one just to the right of the centersuport bearing in your picture. I tightened mine as tight as I could get it and the vibration went away. I have been seeing these things for years on other cars and trucks and always only tightened them hand tight. Give it a try. |
I've got a similar "thrumming" problem on my 300E at medium/high speeds. New engine & tranny mounts (which were shot) improved the vibration 80%, but there's still a lingering problem. I replaced the driveshaft with a used one (not a fun job)... NO change! The U-joint, etc all appeared to be fine. Flex discs are old but in good shape. The center nut is medium tight (see next post). I'm at a loss to explain it... I'm tempted to install new flex discs, but I'm selling the car and don't want to dump money into something that isn't going to cure the problem. I'm tempted to try the vibration damper from the TSB's below, but it is very expensive ($200!). I'd sure like to fix the problem though. One thing I haven't tried is the balancing weights. That seems very time consuming but I may have to try it anyway.
:( TSB - Booming (thrumming) in speed range from 110-150 km/h (70-100mph) : http://www.w124performance.com/docs/mb/W124/driveline_vibes_early124.pdf http://www.w124performance.com/docs/mb/W124/driveline_vibes_late124.pdf |
Quote:
:fork_off: |
Oh yeah - here's the PDF file on driveline balancing:
http://www.w124performance.com/docs/mb/W124/driveline_balancing.pdf Note As a remedy against humming noises with rough spots in speed range between 100 to 150km/h, balancing nuts or balancing washers can be attached to joint flange of rear propeller shaft. But find out first during a test drive whether a complaint is justified. Here, unavoidable dispersions must be allowed for in individual cases during series production, which may be located at upper tolerance limit, so that minor noises should be taken into account. :wacko: |
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