I decided to replace the center bearing on my 85' 300D turbo after procrastinating the job for some time. The support bushing was totally shot allowing the shaft to be easily displaced with very little hand force. Using the advice from a couple of forum threads , I carefully marked the drive shaft halves as well as the mating yokes on both the transmission and differential. I was very careful in the disassembly and assembly of the new center bearing to the shaft. I replaced both flex disks as well since I had the car part. It all went together very well and I assumed it was fixed. Later in that afternoon, I needed to run a errand so I decided to take it for a test run on the freeway. It seemed just fine until I got my speed up to around 55-60 mph. From that speed up, there is a very annoying vibration coming from the draft shaft. It's seems obvious that something I did has caused the shaft assembly to be out of balance. Intuitively, the flex disks are very large in diameter and seem like they would contribute significantly to the overall balance, but that's just a hunch. I'm driving a non-highway cruiser until I can get this fixed. Any suggestions on how I can get to the bottom of this would be greatly appreciated.

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1985 300D Turbo California Model (134K)

Three things come to mind:
1.The "Centering Bushings" in the Flange Ends
(Facing Outwards,away from the Propeller Shaft itself,Inserted into the Ends.)
Are Buggered (Either by Wear,or in the R+R process).
It's implied that wear on them allows you to tighten the Propeller Shaft
Flanges on either end,along with the Flex Disc to Tranny and Flex Disc to
"Pumpkin" BOLTS in an Unaligned state upon Re-Installation of the Driveline.

2.Suggestion in the FSM that BEFORE the Center Support Bearing Holder's Bolts
are tightened to Torque the chassis is rolled back and forth 15-20 Ft. to allow
"Settling" of the Driveline.
AND the HUGE nut on the Sliding part of Propeller Shaft
(Where the Two Parts of the Propeller Shaft are Joined)
Should NOT be Torqued until the Roll/Roll procedure is completed.
All of the Torquing is to be done with the Chassis in "Road Ready" position
[On It's Wheels] (Jacking up the Front or Rear,separately throws all that
"Settling" Out of Whack)

Of Course the Deutschlanders don't tell us how to do all that without a Drive
on Four Post Lift!

Me? I put all four wheels on ramps (After the R/R procedure) and "Bounce"
the Chassis Up and Down by hand 2-3 times at each corner to make up for
any Mis-Alignment when I raised the Chassis onto the Ramps.Then Torque.

3.Hunter's Cautions about Flex Discs:
In which direction the Flex Discs should face
(Some of them Have a German word for Front/Forward on them "VORNE")
AND the Metal Tubes Bonded inside the Discs have Offsets.
Three of them are to connect with the Flange,Three of them to the Tranny/
Pumpkin.

Flex Disc Orientation, safety and durability issue.



Hopefully, You'll have gotten a good night's rest before you see All This
"Good News".

The "Copper" looking Tube inside the Flex Disc and the Flange in the Picture
is the "Centering Bushing"

Attached Thumbnails

 

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'84 300SD sold
124.128

Another way is to roll the car or set the car down onto a set of slip plates (lino / steel / something thin but smooth with grease in between). You only need to do this on one wheel.

And if we're talking 1985 W123 300D don't forget the adjustment of the gearbox mount as well...

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1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

I did this same job on my buddies 85 SD a few months back with the same result. I even replaced the transmission mount. Had everything apart 3 or 4 times trying to figure it out and never did. My guess is a bad part. Lucky for me he says it doesn't bother him much since he rarely drives on the highway.

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Compress Ignite and Army,

Thanks for the input for "settingling" the chassis before tightening the nut. I did not do that on this job. I was very careful to install the flex disks with the raised pilot shafts into the flange as Hunter illustrated. I did not see any German Markings suggesting "front" but I will do a thorough inspection and try your suggestions and retighten the nut. I'm willing to do quite a bit before I resign myself to take the drive shaft out again !

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1985 300D Turbo California Model (134K)