Advice on changing Automatic Car to Manual and are the manual gearboxes different between engine sizes?


Looking for advice my car is a 3.8 with a borg warner dg250 auto box possibly looking at converting to manual gearbox, my question is are all the mk2 manual gearboxes the same (ie will a box from a 2.4 fit a 3.8 or is gearing different for rear axle etc) or do I need a specific gearbox for the 3.8 model to match with existing set up, Any advice or tips about the type of box or any pointers on converting to manual would be greatly appreciated as always! Regards Paul.

I am not sure about internal ratios but what you should be looking for is a 1965 model year or later full syncro gearbox as they are more advanced and easier to use than the older Moss box used from 1964 and earlier. I believe the gearing differences between engine sizes were done with the final drive ratio. Automatic 3.8 cars used a 3.54 ratio, non overdrive manual cars also a 3.54 ratio but overdrive cars a 3.77 ratio. Many prefer the 3.54 even if the car has overdrive as it give lower engine speeds on the highway. The full synchro box had the reverse position to the left and back, Moss boxes to the left and forward.

I have a 240 , it was a Auto , have used a 240 manual gearbox bolted on the back of a 3.4 XJ6 engine , Axle is still the 240 Auto , I drive mostly on country lanes , so the gearing is not a problem !

Many years ago I replaced the DG box with one from a S1 XJ6
As stated this was many years ago so memory has faded somewhat but I do remember having to machine the bell housing to move the starter motor so that it meshed with the flywheel.
This was the all synchro O/d box, very happy with the difference in driving experience although I also had a change of diff ratio, instead of the correct (Jaguar) ratio of 3.77 I blew my diff and the only C/W and Piñon I could find here in NZ was 3.07
Allowed great low RPM cruising but takeoff was a little compromised.
This was with the 3.8 I am currently changing this box into another ‘S’ but with a 3.4 sowill leave the diff as is at 3.54

Thanks for the info John plenty to think about, regards Paul

Thanks robin for the info and Mentioning some of the pitfalls if not done right, regards Paul

Thanks Ian for the info, regards Paul

I’m about to embark on converting my 3.8 mk2 from a chevy 700r4 to a T5. Will post a detailed thread but there are loads of small bits to collect and then putting together the right combination of bellhousing / flywheel / starter that all match. Then install the clutch system, cut a hole for the shifter, and (I think) shorten the driveshaft.

Here’s a simple spreadsheet with original ratios info, with my T-5 comparison calculations.
Does not handle 3.8 info, wheel sizes variations.
Can’t link xls, so just a screen grab, want xls - shoot an e-mail address.

Thanks it sounds quite a job, regards Paul

Many thanks for the guide with different ratios, regards Paul

Hi Paul…if you go for a 4 speed all syncro box you will have to change or machine your bell housing…you will also need a flywheel from a manual car…with teeth to match your starter motor (just count the teeth on your existing flex plate)…or fit a different starter motor…Steve

Thanks steve for the info lots of people saying go for all synchro box and at least I now know about what’s needed many thanks Paul.

I’ve got everything you need if you want to go that route. But since the vast majority of Mk2s had the Moss box it isn’t exactly a disaster!

Hello peter I will get some prices for shipping and will let you know, regards Paul

The overdrive on the 2.4 box has less springs and less pressure.Could be a problem when switching to a 3.8 engine.

I recall a similar question on this forum many years ago, one issue not touched on here was that the transmission tunnel needs to be larger for either the manual or auto trans, I am sorry I forget which. I recall the solution involved beating the smaller one out with a hammer?
P. Smith

The auto required the larger tunnel so retro fitting the manual is a breeze, I recently removed the 4sp o/d from my ‘66 ‘S’ with the car on axle stands. The car was originally an auto. Its going into my ‘65 ‘S’ (also changing from auto)

Thanks Robin, regards Paul.

Hello CarsonSmith yes Robin has mentioned about the gearbox tunnel, he said as my car is auto and been larger might get away with that, regards Paul.