Transmission Slotted Nut

[Leester]

Hello all, I recently installed instruments in my project car, 1970 280SL, standard transmission and took it for a quick drive. Speedo started bouncing. Uh oh. Read up numerous old posts with warnings about the slotted nut at the rear of transmission. Getting ready to send speedo out (it needs recalibration due to 3.27 rear new to this car) but I'm still concerned about the slotted nut.

Getting at the slotted nut will require a fair amount of disassembly underneath. It seems like if the slotted nut is loose, there will be play, forward and aft, at the centering cross. If that is true, it also seems like loosening the driveshaft sections would enable me to push and pull on the forward drive shaft section to feel the play.

Obviously I'm looking for a short cut and hoping someone can let me know if loosening the forward driveshaft from the rear, and pushing and pulling the forward section of the driveshaft against the rear of the transmission will identify play and therefore a loose slotted nut.

Many thanks in advance.   

[Benz Dr.]

Remove your speedometer cable from your transmission. Insert a flat bladed screw driver into the speedometer drive area and turn your driveshaft by hand. If you can turn your driveshaft without the screwdriver moving, it's loose.

 

[Leester]

Many thanks Dan. Will give that a try.

[rwmastel]

If you can turn your driveshaft without the screwdriver moving, it's loose.

Moving fore/after or rotating?

[Benz Dr.]

Rotating. It's the only way the speedometer drive will also rotate or move.

[Leester]

Thanks Rodd and Dan for that clarification. My thinking in the original post was that if the slotted nut was loose, there would (should?) be fore and aft play in the front driveshaft.

But that's unrelated to Dan's approach. I followed Dan's instructions and the screwdriver turns when I rotate the driveshaft, with no play, so I think I'm good to go. Speedo is off for rebuild.

Many thanks guys!