Fitting an Overdrive to a 240 all-synchro Manual Gearbox


A potentially tricky one?

A good friend has a non-overdrive all-synchro gearbox from a 240 fitted to his 1960 3.8L MKII. He has been given an overdrive unit from a 3.8 MK2 in good working order and would like to fit it to the all-synchro gearbox. Is there anything stopping this from being a straightforward fitting?



Yes, plenty!
He will need to swap the output shaft from the non overdrive box with the longer one from an overdrive box.

As well as the two switches / relays on the top of the gearbox now that I think about it. Looking in the MK2 Spare Parts Catalogue, the Part No. of the overdrive is different for the 3.4 & the 3.8. What are the differences I wonder?


The actuating pistons in the 3.8 are slightly larger than in the 3.4. I don’t think this would make any difference unless you were racing or rallying. Makes a difference when ordering spares though!

The ratios probably vary with a lower first gear. The ratio drop may also be handled at the diff.

Assuming both boxes are all synchro just swap as intact units. If the 3.8 is Moss, I’m not sure the Type A OD will fit the 2.4 box as it is a very different type from the Compact Type A fitted to all-synchro cars.