Vintage Cars: Over Drive 1979 MGB LE, od units, moss motors

Question
Did all the 1979/80 LE's come equipped with Over Drive? If not can you tell me who would know how to determine what cars were equipped.  I have a 1979 LE but the trans. shift knob is for OD but the trans is 4 speed standard? Help

Answer
This is actually much later than my expertise, and this source explains it much better than I can.

http://www.mgcars.org.uk/news/news363.html

The switch on the shift knob is apparently there on all late B's, but only some actually have OD. I think the best thing is to look underneath and see if the OD unit is there. It sticks out about another 4-5 inches, bolted onto the rear of the standard gearbox. And it (obviously) has electrical connections for switching it. (A Moss Motors exploded diagram from their web site should tell you roughly what the thing looks like.)

If nothing happens when you switch it, either in or out, it's quite possible that the car has no OD. But if it does have one, but it doesn't work, fixing an OD unit can be quite difficult. The most common failure with OD units is the oil (the gear shifting in the unit is hydraulic ). So checking/changing the oil is the first move (20/50, not gear oil); then the filter in the OD body; then check the circuit, i.e is the solenoid actually switching...etc...

JJ