740 Are M46 internal parts exchangeable?

I have the original aluminum case M46 from my '86 745T. It chewed up a syncronizer hub years ago at 144,000 miles and has been sitting in a box since. At the time, I swapped in a lower mileage junkyard cast iron case M46 from what was marked as a '88 240.

I also picked up 2 free complete (but with undiagnosed issues) cast iron M46 gearboxes for parts. I was told the 2 parts transmissions were from early 80ish cars. My intention was to rebuild my original gearbox. Fast forward 8 years, and it's time to start this rebuild.

My question is are the internal parts identical and interchangeable between aluminum and cast iron M46s?

I didn't see any type-tags (like a M4, M40 or M41 has) attached to any of the gearboxes but did see the following numbers embossed on the side of the gearbox cases:
Part # of the aluminum box appears to be 1023571;
Part # of the 2 cast boxes appears to be 1023584.

Maybe someone could point me to parts lists and exploded views of both style gearboxes.
I found some exploded views online, but didn't see part numbers specified.

Also, was the aluminum gearbox only used on turbo cars?

FWIW, I have a couple from diesel cars.

alschnertz said:

Also, was the aluminum gearbox only used on turbo cars?

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I think 240s got iron and 7/9s got aluminum. I'm not sure that's right though.

Hoggster said:

I think 240s got iron and 7/9s got aluminum. I'm not sure that's right though.

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Iron case till 86 on 240's and then the M47 in 87.

Not sure but I think the early 700's got iron cases early as well although I'm not sure when they went to alloy.

84-85 if I had to guess?

To answer the OP's question the late 'P' type OD M46's have a bigger main shaft, so no not all M46 internal parts are compatible.

Really early transmissions used a bronze bushing instead of a caged needle bearing on the main shaft gears.

On later transmissions there's a change in the 1st gear ratio from 3.71 to 4.03:1. With a few exceptions, most of the internal parts will interchange. M47 gears are even the same.

Greenbooks:

M45/46 '76-'78 (Swedish)

M45/46 '79-

M46/47

Redwood Chair said:

Iron case till 86 on 240's and then the M47 in 87.

Not sure but I think the early 700's got iron cases early as well although I'm not sure when they went to alloy.

84-85 if I had to guess?

To answer the OP's question the late 'P' type OD M46's have a bigger main shaft, so no not all M46 internal parts are compatible.

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My '85 764 Turbo came with an alloy case. It is a pretty early car with a steel gas tank.

All my gearboxes are J-types.

Shoutout to hiperfauto for the greenbooks. Those are awesome.
I've rebuilt a few M4s, M40s and M41 Ds & Js. I'm betting that the M46 should be similar.
Maybe I'll even be able to cobble together 2 good gearboxes out of all the parts. It will be nice to get the original box back together.

Many thanks to all for the information.