Driveshaft Vibration Cure
 

Well, after pulling the exhaust system a few times to get at the driveshaft and try different things, I have GREATLY reduced the drumming, thrumming vibration in my driveshaft. After going through all this, if I had it to do over again I think that I could have fixed it in fifteen minutes if I had known then, what I know now.

After pulling down the driveshaft, some time ago, to replace the front flex disk, I picked up the vibration. I had some tire problems at the time, so I didn't confirm the driveshaft vibration until I sorted out my tire problems which was a broken belt that was hard to find.

After the tire problems were taken care of, I thought that maybe I had not gotten the shaft splined up correctly, so I pulled the exhaust to check. I had indeed marked it and everything was cool. Since then I learned that there are permanent marks on the front and rear of the shaft from the factory, and they were indeed aligned properly.

I tried following some factory info, that said to unbolt and turn the shaft 120 degrees at the transmission and try it again. That did nothing. I then bought a transmission mount thinking that maybe it had come down some causing a bad angle. At the same time I got a carrier bearing and support and a rear flex disk. With all these parts on hand I was ready for the attack.

I got all these parts and pulled down the exhaust and shaft yesterday. The transmission mount was indeed much softer than the new one, and the rear flex disk was pretty cracked, so I put in the new parts. With the driveshaft out I was able to spin the carrier and evaluate it better than when in the car. It seemed in real good shape as did the support.

While the shaft was out, I rotated the u-joint on both axes. The joint had a "detent", or a notch in the center. It seems that it must be worn in that specific position in which this joint almost always stays. In these cars, the shaft probably never flexes over one degree, so the joint only wears in that specific spot. In fact, I really think that once you pull down the shaft, flexing the u-joint some 15 or 20 degrees, you might be causing something to happen inside those bearings because you are moving them out of their wear zone. Maybe this somehow causes the "detent" to occur.

I removed the harmonic weight while I had it apart, and before reassembling, I cleaned and greased the splines and the centering bushings and pins on both ends of the shaft.

I put everything back together and road tested. I could tell no difference.

With knowledge of the "detent" in the u-joint, I decided to move the carrier bearing position slightly to see if running the u-joint through a different arc might make it happy, and it did.

By taking loose the three 8mm screws on the converter heat shield and rotatiing it to remove, I had access to the carrier support. I loosened the vertical bolt on the drivers side and removed the one on the passengers side that is at an angle. I put a few washers between the carrier support and the chassis mounting hole, then put the bolt back in and tightened everything up.

After putting the heat shield back in, I was done. It took about fifteen minutes. I don't think the vibration is 100% corrected, but it is almost completely unnoticable.

There are two possible lessons here; the first, don't pull down the u-joint causing it to flex beyond it's normal angle unless absolutely necessary, secondly before going to all the trouble of removing the exhaust et al, try slightly changing the position of the carrier support to see if the vibration goes away. You can do it in fifteen minutes. It's worth a try.

I'm very relieved as I was beginning to think that I would have to buy the rear driveshaft portion for over $500. That's the only way to replace that u-joint. Given my recent career woes, that was not a very attractive alternative.

Sorry for the lengthy post, but I thought that it might help someone who is living with driveshaft "thrumming."

Have a great day,

Larry,

Persistent little sucker, aren't you. :D

Larry,

Thanks for posting this - that's pretty creative troubleshooting! I've had this problem with my 300E for awhile - eventually R&R'd the tranny mount, center support, and had the driveshaft bearings replaced, which has helped a lot, but the vibration isn't totally gone. Might try this at some point, depending on whether the vibration eventually gets worse again.

Incidentally, when the driveline shop was checking the driveshaft, they also found a "detent," or some resistance, in the bearings too.

larry which one of your cars were you working on?

Great Post Larry, I was going through the same procedure so many times that right now I can do the driveshaft with my eyes closed. I also started greasing the u-joint, even through everything flies preatty much right off it, some will always seek into cracks and help the shaft live longer.

I also did not hae any problems when bending the shaft further then it does while installed, if that creates a problem, I would say the bearings are worn out and should be replaced.

That driveshaft is one delicate piece of heavy duty metal :)

xp

Sorry, this was on my manual transmission 300E.

I guess my "detent" terminology did not adequately describe what the joint was doing. At the point where the shaft is virtually straight, it takes a little pressure on either axis to move the joint. Once past this pressure point, the joint is smooth as silk.

Have a great day,

what speed was the vibration?
 

Larry,

I also have a vibration I'm about to go after. What speeds / rpms were your vibrations most noticable?

Chuck

thanks for the clarification larry.ive got a vibration problem with my 90m 300 te 4matic and i suspect driveshaft alignment.im gonna give your method a try

Chuck,

MY vibration was at about 70 to 90 MPH. It was a droning or warbling, high frequency vibration. Tire vibration is MUCH more common and is at about a third the speed of driveshaft vibration.

If you're not sure if it is driveshaft or tire related, rotate tires and see if it feels different, if so it is tires, if not the next most likely possibility would be driveshaft.

That said, you need to think through a vibration before acting. If you kick it in neutral, does the vibration remain, if not it might be engine related. Does the vibration follow engine speed or vehicle speed?

Don't start doing things like I did without first determining that it is indeed driveshaft related.

Tires MUST be dynamically balanced on these cars. That means weights inboard and outboard on the wheels.

Good luck,

more vibration info....yuck - edit
 

Folks,

I moved my response to a new topic.

Chuck

1997 E320 vibration
 

Larry, I just read your post about vibration and how to determine where it might be coming from. My car has been vibrating at about 55 mph and just today I realized that it was engine rather than road speed that determined when I would have the vibration. I had my tires balanced to eliminate that possiblility. And, while they were out of balance, this did not solve the problem. Today I noticed by shifting into different gears that the vibration was occurring at about 1800 rpm regardless of which gear I was in. When cruising on the highway, I pushed the gearshift lever into neutral several times and the vibration seemed to stop. I feel that this indicates that the vibration must be coming through the engine. The last trip I took in this car I recorded 30 miles per gallon; so, I wouldn't think that the engine is out of tune. Is it possible that a spark plug, a wire, or some sensor may have gone bad since my good gas mileage? Any help would be appreciated. Thanks for any assistance, Big Ron

Big Ron,

You might want to get with an MB dealer and check the part number of your harmonic balancer. Some were recalled.

Good luck,

1997 E320's still had the M104 engine, so he wouldn't be affected by the harmonic balancer issue.

I would suggest having your motor mounts / transmission mounts looked at.

Do you get any sort of vibration at idle?

Vibration
 

I don't think it vibrates at idle but it seems a little rough when I give it the gas while sitting. This is our third car so I don't drive it much but I want to figure out what's wrong with it now, so I can fix it as soon as the weather warms up a little (really a lot). Thanks a lot, Big Ron

If you rev the engine to 1800 in neutral, do you get the (same) vibration as when the car is in gear at 1800 rpm?