Rear end parts interchangeability?

XJ-S
21

If you have the earlier electric speedo with the transmission mounted transducer there is no signal processing. The signal from the transducer goes right to the speedo, trip computer, and cruise control.

If you have the later type with the differential mounted sensor then, yes, there is a ‘speedometer interface module’ to process the signal.

On my car, with the earlier system, I used a right angle ratio adapter to correct the speedometer error, GM #1565208. It slows the transducer rotation to give the needed 17% correction. The adapter attaches to the transmission where the transducer normally fits. The transducer then attaches to the ratio adapter. Tight fit, physically, but it worked.

The link below shows a right angle ratio adapter just so you get an idea of what it looks like. It isn’t the one I used.

Cheers
DD

22

have not touched a th400 in over 10 years. I have had th350’s, 200 4r and 700r4’s apart and all are similar at speedo drive. the speedo gears are at the rear of the trans, one can be removed from outside, the other slips over the shaft and requires removal of tail housing. the gears are available in different sizes so correcting speedo usually isn’t a problem and often can be corrected with just the external gear. worse case scenario, you would need the tail housing from another trans. and the gears. https://www.youtube.com/watch?v=WTngjBKes00