If the P.O. changed the engine, but not the transmission, that is why your original speedo was working.

The ONLY transmission that works in an 81 TD is the original 81 trans... the tach pickup would be on the engine intermediate plate, not the transmission... it picked up off the flywheel.

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!