Hello Gary,
At the tech session last summer we correctly diagnosed and identified the same problem with another members pagoda. When Graham got back home he had his mechanic repair his transmission. I sent the following documentation to his mechanic so they he correctly repair the problem. Here is a copy;
If your speedometer has become irratic, and your transmission is not shifting smoothy, the slotted spanner nut on the output flange of the tranmission may have come loose. This slotted nut holds the entire third fourth gear cluster tight. In addition the drive gear for the speedometer is NOT keyed to the shaft but depends on the tightness of the cluster and slotted nut before it can operate correctly.
Consider inspecting and replacing the rear tranmission mount, the drive shaft rubber flex disc, and the rear transmission seal if needed during the transmission work.
Start by removing the multi-bolt tunnel plate and transmission mounting plate. Remove the rear transmission mount and bracket. Remove the 19mm driveshaft bolts. Pay close attention to the configuration. There are three long bolts and three shorter bolts. Refer to the information and diagrams for re-assembly. This must be installed exactly or the rubber disc will not last or will come apart.
The drive shaft has a slip joint half way back. Loosen the 44mm and 46mm slip joint and slide the drive shaft rearward. This will allow you to split the drive shaft at the drive shaft flange/centering bushing connection and enable you to remove the flex disc, and move the drive shaft out of the way.
Download Attachment: 
assembly.JPG66.29 KB
Check the slotted spanner nut for tightness. If it is loose it must be re-tightened. A special four prong socket is still available from Mercedes for these nuts. Some mechanics make their own with a die grinder and a 1/2" drive 1 1/8" deep well socket. In a pinch the nut can be driven tight using a drift and hammer (not recomended). The sheet metal lock ring must be "staked" outward and inward to prevent the slotted nut from comming loose again.
This is a picture of the speedometer drive gear. Notice it has no keys or teeth on the inside to keep it from spinning on the shaft. The pressure from the tight spanner nut keeps it from spinning. If the spanner nut comes loose the gear can no longer function correctly.
Download Attachment: gear.JPG73.17 KB
Download Attachment: parts.JPG69.89 KB
Here is a picture of the gear on the shaft;
Download Attachment: shaft2.JPG67.95 KB
Before re-instlling the flex disc, check it for conditon also note that the three tabs on the flex disc MUST be postitioned on the three flanges of the transmission out-put shaft (see diagram).
Download Attachment: late11.JPG52.81 KB
Notice locations of the long and short diveshaft bolts and the washers. Review the diagrams, this is critical. Notice that three of the washers are positioned under the bolt heads and the other three under the nuts of the other three bolts. In every case the washers are positioned next to the rubber flex disc. The nylock nuts can be reused if the condition is ok and everything is re-assembled correctly. The driveshaft bolts should be quite tight and you may feel the nuts bottom out against the bolt shoulder as you tighten them down.
Download Attachment: eflex 20.JPG84.64 KB
Here is an excellent photo with text by Bob Possel;
Download Attachment: Bob Pflex disc.jpg41.1 KB
Pump a bit of grease into the driveshaft end at the Zerk to lubricate the centering bushing assembly.
Install the transmission mount paying attention to the spacer washer between the mount and the mounting plate. Tighten the drive shaft slip joint last after the tranmission is secured.
Good luck!
Joe Alexander
Blacklick, Ohio
