Cadillac Repair: speedometer, cadillac brougham, digital speedometer

Question
analog. if you are driving down the road and put the car in neutral the speedometer works instantly and stops instantly when put back in gear.
-------------------------------------------
The text above is a follow-up to ...

-----Question-----
1988 cadillac brougham, 5.0
speedometer works only in neutral, not in when in drive, at any speed.
Thanks

-----Answer-----
Analog or digital speedometer ?.

Explain how it works in neutral vs in drive ?>

Answer
This is one I have not seen yet. Check the black speedometer cable where it comes thru the firewall under the brake booster and make sure that the transmission gear linkage is not interferring with the cable as it is possible that it may be stretching the cable.

Next would be to remove the 10 mm bolt from the transmission and pull the cable out of the transmission and check the gear on the end of the cable and check the gear in the transmission and see if you can move the one in the transmission.