Hi everyone,
I am sure someone here has tried or knows.
How difficult is it to add an OD unit to an existing M40?
I am going to try to spend some time today looking through my manuals and schematics (spelling?) and get a feel for how the go together.
Thank you,
CU

It is MUCH easier to replace the existing M40 with a different M41 and
probably cheaper too.

Be sure and get the front driveshaft, crossmember, and whatever else looks
different from the donor car. With that it is a bolt-in.
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George Downs Bartlesville, Heart of the USA!

To "add" od to an existing M40 would require a new top cover, main (output) shaft, rear housing, speedo drive, etc. It would be easier and cheaperto get a complete car and transfer parts. Or pick up used components. You would need the trans, at least the front half of the drive shaft, the cross member, and a switch and wiring.

Not worth the effort. The output shafts are different - that means you need a complete 'donor' M41 anyhow - and you'd have to pretty much *completely* disassemble both boxes to swap that. And the cases are different - although only in that the M41's fill hole is slightly higher. Based on the fact that you need an M41 anyhow, you might as well use IT instead of any M40 you have. As far as swapping various parts between an M40 and an M41 - beware the various brealy perceptible changes over the years. Other than the much longer output shaft they are the same, but from my experience the odds of parts swapping between any two M40's or M41's is not that great. Check part numbers before trying any interchanges. Syncro cones don't seem to have changed much, but gear sizes, layshaft sizes, and roller bearing sizes all made various changes over the years.

A couple of winters ago I tried fixig my junkyard M41 (nice gears and OD, but syncro's #1 and 3 were totally non-op) using my original M40 for parts. After some carefull study I found that the ONLY parts that would interchange were the syncro cones. Luckily, that was all I really needed.
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I'm JohnMc, and I approved this message.

Thank you for the responses. This will save me a lot of headaches and doing a lot of fruitless work.
CU