I just replaced the center bearing rubber mount. Then old had 1" of circumference remaining. The bearing is OK. The rubber flex disks do not show any cracks or rust around the inserts.
The rubber is still flexible but firm. Although original they appear to be in good shape. Before removal the drive shaft was punch marked to guarantee correct reassembly.
Now the vibration is worse but different than with the worn out center bearing support. What have I done wrong?

I find it strange that I have to use a pry-bar to remove the drive shaft. If the drive shaft was only 1/4" shorter that would solve the problem.

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1984 300SD turbo 126
"My true love"

God made me an atheist and who am I to question His wisdom

if you loosen the big nut on the drive shaft spline so it can be compressed, then remove the rear flex joint from the diff, drop it down and remove the drive shaft from the flex on the front it will come right out. if you were prying on it then it may be thrown out of kilter by that. make sure when you reassembled that you put the flex joints on in the right direction, they are set up to take the load in one direction and can be assembled wrong. other than that you can try the old hose clamp balance trick by putting a clamp on the end and moving it 90 degrees until you get the vibe out

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1982 300CD Turbo (Otis, "ups & downs") parts for sale
2003 TJ with Hemi (to go anywhere, quickly) sold
2001 Excursion Powerstroke (to go dependably)
1970 Mustang 428SCJ (to go fast)
1962 Corvette LS1 (to go in style)
2001 Schwinn Grape Krate 10spd (if all else fails)

Thanks for the info lutzTD. I found that getting the rear flex disk over the diff alignment hub was the part where there was not enough clearance and needed a little persuasion with a flat bar, about 1/8" to clear. This is the second time I have done this job on this car since new and once on a 74 340D. Never had any trouble before and always had to use a bar to drop the shaft. I have read of others with the same clearance problem. Hate to replace the flex disks when they look good.
Doing the job is easy. Getting the car in the air is a pain. Is the a cheep floor lift on the market that can just lay on the garage floor and park on top of it between jobs?

__________________
1984 300SD turbo 126
"My true love"

God made me an atheist and who am I to question His wisdom

Is the U-joint intact? My 240D had one go bad causing vibration.

John

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Certified Registered Nurse Anesthetist (CRNA)
2002 F250 powerstroke with Plantdrive WVO conversion
1983 300SD 190K miles ,sold
2006 E320 CDI

hangit: the U joint did not feel loose or have play in any direction.
I will raise the car to day for a better look at the front disk. May have been damaged in the prying process.
let you know what I find.

__________________
1984 300SD turbo 126
"My true love"

God made me an atheist and who am I to question His wisdom

Went to Driveline Services. they removed the drive shaft, inspected the flex disks and declared them OK. Also the center bearing and universal in good shape.
Set it up in their balancing machine. I ran smooth at all speeds. the balance machine did not ask for adjustment. Back in the car, guess what. Just the same as before. The Drive line guys have no answers and say they have never seen a shaft run perfect in the balancer and shake in the car. Unless the frame is really bent, but not the case here. Stymied.

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1984 300SD turbo 126
"My true love"

God made me an atheist and who am I to question His wisdom

A wheel weight flew off? Check all suspension components too, good luck.

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83 SD

84 CD

Check to make sure the three-bolt "yoke" is still bolted tight to the transmission. That's the part in front of the front flex disk that normally stays with the transmission. Sometimes the nut that holds it on can get loose and then the yoke gets shifted a bit during the driveshaft installation process. Easy to check if you have the driveshaft out. Just grab the yoke and see if there's any looseness or side play.

Not likely to happen, but another idea for you to check.

Also, the driveshaft assembly process in the manual specifies that everything should be assembled with the big locking nut loose - then the car rolled forward and backwards some distance (30 feet) and then the nut tightened up.

These driveshafts are extremely touchy to deal with in terms of vibration. A one U-joint design is pretty sensitive to alignment and balance, particularly if it has worn 250,000 miles one way and then it gets re-aligned slightly differently.

Ken300D

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1982 300D at 351K miles
1984 300SD at 217K miles
1987 300D at 370K miles