m47 swap ?
 

I've managed to finally find an m47 to throw on my 82. I know that they came stock with the m46 because of the stronger casing, but I really wanted the actual fifth gear. I've opened it up and everything seems to be in very good condition. I'm not planning on throwing any crazy power at this car because it is my daily (maybe a turbo at some point the lack of power is a bit annoying). But I was wondering if anyone with more knowledge on d24s would see any issue with putting the m47 on there.
I'm already planning on having the front driveshaft shortened by a driveline shop, I don't know if theres any differences between the gas m47 driveshaft and the diesel one but I can't get my hands on either.

Nice! A few others of us on here have considered this swap as well. The electric OD on the M46 can be fussy for sure so the simplicity of a conventional overdrive 5th gear on the M47 is appealing. Plus the M47 is far lighter and smaller than the M46 due to the big OD unit hung off the back, saves a little weight and easier to handle during clutch replacements, etc.

I highly doubt the difference in strength could matter much even behind a D24T unless it were in the hands of an abusive operator. And behind a NA D24 it should be completely fine since the later year 240 diesels without turbo did come with M47s (late 80s when they went into the NA gassers also). To my knowledge the M47 never went behind a TD from the factory but that would likely not stop some of us with 7 series cars from trying it someday if the parts materialized.

As for swapping it for an M46, believe there would only be a few keys to success:
- Need to swap the diesel M46 bellhousing, possibly the clutch release fork, and definitely the sleeve on the end of the input shaft over to the gas M47. That sleeve is important since the gas engines use a pilot bearing with a smaller ID than the diesels. So if you forget to swap the sleeve you will have no support on the trans input shaft and it'll beat the trans bearings up quick. If this doesn't make sense the way I'm describing it don't worry, you will see what I mean as soon as you get the diesel trans out of the car and compare the input shaft to your M47. It should pull right off of there with a standard puller, maybe a little mild heat to help.
- Shift linkage might require some careful comparisons but if your M47 came from a 240 I would imagine it would drop right in.
- Driveline: all you need is the front half of the driveshaft from an M47 car and it should all go together with no fuss and no custom driveshaft work except maybe balancing it if you're using a front half from a different car and the rear half you already have. Note that you will actually be lengthening not shortening the driveline overall. The front shaft is longer on M47 since the M47 trans itself is considerably shorter than the M46. The connection at the trans might also be different since the diesels all always used flat flanges but the gas cars often used rubber guibos so that may be what your trans is set up for.

Finding a M47 front driveline section from a 240 should not be that hard? Any manual trans gas engine 240 from 1987 to 1993 would have what you need. Try asking on Turbobricks, those are pretty common cars and someone might have a parts donor sitting around.

Let us know how it goes, after having M46 OD relays and 4th gear switches fail more than once on long trips in the middle of nowhere and having to hotwire to get home, I would consider the M47 an upgrade. :) Just fewer things to screw you up.

Does your M47 have a mechanical speedometer drive? M47II gearboxes do not have one.

Good point on that. I always forget the early 200 series cars used mechanical speedometers. Too accustomed to the 700 series which were electronic speedo reading off the diff for all years of their production. :o

Did M47I have a mechanical speedo cable drive? So if he could find an early year M47 it would work but M47II would not?

Thanks for the help! That's all very useful, I'll try looking around for an m46 bellhousing, but I was also considering doing something like this https://forums.tdiclub.com/index.php...inside.476340/

I was looking around for the sleeve last night, can't seem to find that either. Maybe I'll talk to some vw shops, there are so many in my area. But in the end I'll probably need to fab that myself too. This car has forced me to do so much custom work due to the lack of parts, love this thing but it's really making me consider doing a redblock swap if it ever truly shits itself lmao.

I'm so glad I found this m47 though, mechanical parts are just so much easier to fix than electrical issues. the m46 design is definitely strange, but I guess volvo was just trying to be more advanced.

Many directions you can go if you get overwhelmed. LS swaps seem to be popular. A lot of fab work and chasing parts involved there also. What are your goals and desires?

Depends on your skills and tools.

I don’t know if the M47I gearboxes (84-86) had a mechanical speedometer drive, the two M47II gearboxes I’ve had were in 87 and 88 240s, the speedometer gets a signal from the differential like 740s. It’s not as completely crummy a gearbox as claimed, but my opinion is based on the later version with an improved fifth gear.