m47 to m90 gearbox (UK PEOPLE)

[barkster1971]

Hi my 1984 760 has the M47 gearbox (OD in green on the dash ) and I wish to put in a 940 td M90 gearbox.
Does the prop from the petrol M90 cars fit? Anything I should look out for? The 940 M90 clutch is going in too. I presume the flywheels are the same?
Thanks, Carl.

[v8volvo]

You might want to see if you can get a copy of VADIS or VIDA (Volvo electronic parts catalogs) as those would answer all questions about what parts work where. I would assume everything from the 940 M90 setup would bolt right into the 760. But, you will probably need to bolt in quite a large number of parts from the 940 if you are putting the M90 in place of an M46/47 because to my understanding there are many differences, not just the transmission and propshaft and clutch/flywheel. E.g.:

- M90 uses a hydraulically actuated clutch rather than the cable found on the M46, so you will need the complete clutch hydraulic system from the 940 (clutch master cylinder, fluid hose to brake master cylinder reservoir, fluid line from master to slave, slave cylinder, hydraulic clutch pedal and pushrod, and firewall plug to seal up the hole where the cable currently passes through)

- Late style engine and transmission mounting system as found on M90 equipped cars is different from the shear-style solid mount system found on the early cars and parts from the two systems are highly incompatible. The late style uses vertical mounts for both engine and trans while the early style uses angled mounts for both. Trying to mix and match parts from both mounting systems won't work as it will cause the engine and transmission (and driveshaft) to shift to the incorrect position causing lots of problems, and will also cause all three mounts to fail after a very short time. You would be able to bolt the late type vertical trans mount (with its original 940 trans crossmember also) from the M90 into the 760, but to make it work out, you would also need to get the late style vertical ENGINE mounts, upper and lower left and right engine mount brackets, and front engine crossmember from the D24T 940 and swap those all in up front to make it all work correctly. Or, you can fabricate a way to install the old style angled rear transmission mount and crossmember from the M46 onto the M90; that would allow you to keep your existing solid front mounts and crossmember and your trans crossmember but wouldn't be bolt-in setup as you would have to do custom fabrication to adapt the trans mount to a transmission that was never originally built with it.

- Shift linkage for the M90 is different so you would need the boots, pivot box, shift lever, rods, etc.

- The driveshaft for a M90 gas car might or might not be the same for the M90 behind a diesel, this would be an area where VADIS/VIDA catalogs would give the answer. As for the flywheel and clutch, don't know if the flywheel is the same for M46 and M90 but I would not be surprised if they are different. I would just use the complete M90 flywheel and clutch and throwout bearing set if you can get them. Watch for any potential differences in the pilot bearing and transmission input shaft diameter/depth also.

I'm not in the UK or Europe to know these firsthand so can't speak to any other differences I am not thinking of, others with experience may be able to describe more, but just based on the general early/late chassis and mounting differences plus the hydraulic clutch, these are factors to think about that I can point out.

Hope this does not discourage you from doing this since I think it would be a great improvement and worth the effort, and wouldn't be difficult once you had everything since all of the parts should go right into the car with no modifications. But it might require a lot of parts chasing if you don't have a complete donor car, so perhaps will help to know about and try to track down all those pieces ahead of time, instead of after you already have your car taken apart.

[barkster1971]

It's a m46 gearbox not m47. It's not cable operated as it has a remote master cylinder just a bit lower than the brake one that definitely feeds into a slave cylinder. The transmission mounts are there as I know plenty of people who have put an m90 in their 740.
I have a complete m90 box with gearlever.
VADIS is useful and the rear end of the prop has the same part number between the diesel and petrol versions.
I have a m90 228mm diesel SACHS clutch kit.
I am using my brother's garage to do this with a lift and his help!
The M46 overdrive is intermittent- I have just resoldered the relay as I will be going on the motorway to get there.
I'll let you know how I get on.
Cheers, Carl.

[v8volvo]

Good to know, well that sounds like it will all work out nicely then. Having a lift will sure make it nicer, pulling RWD transmissions on the ground is always a chore.

Would be great to see some pictures of how it goes together if you have time while you're doing it. Others have talked about doing this and there is info out there from folks putting the M90 into gas cars but firsthand info on swapping behind a diesel is hard to come by, so it would be fun to look at how yours turns out. Keep us posted.

[barkster1971]

It has been done. However it was a faff. I used a petrol m90 prop. you have to use the 3 bolt flange on the end of box. I'll do a write up shortly.
Carl.

[v8volvo]

Originally Posted by barkster1971

It has been done. However it was a faff. I used a petrol m90 prop. you have to use the 3 bolt flange on the end of box. I'll do a write up shortly.
Carl.

Great to hear it all went together. What are your impressions so far after driving it a bit? How are the ratios, shift feel, noise, etc compared to the old M46?

Look forward to hearing what was involved in the install, definitely let us know. Any special tricks to it? What trans mount setup, flywheel, etc were needed in the end?

[barkster1971]

It was of course a m46 not m47 but the dimensions are the same.
It drives so much better now.
still the same flywheel with a sachs diesel clutch for later 940's (1994-1998).
I didn't have a diesel prop m90 one so used one off a petrol car with the 4 bolt flange changed to a 3 bolt petrol one off the back of my dad's petrol m90.
You need a m90 diesel box with the gearstick assembly as that's particular to the diesel box being a bit longer than the petrol one.
All bolts together nicelt and the car is a lot nicer to drive.
First gear with the m46 was too short.
Plus if I wan to increase the power the box and clutch will be fine.
The m46 overdrive was working only when warmed up so it was no good.
you need the diesel gearbox support as that is slightly different. and a good m90 prop bearing as it's a lot thicker than the m46 one .

[v8volvo]

Carl,

Wanted to see if you would be willing to add some more details on how this setup has been working for you now that you have had it in there for a while, thoughts on whether it's a worthwhile upgrade and anything you would recommend doing differently.

I have been casually looking for an M90 swap kit for my 1983 760 and have now found one, complete with shift linkage, driveline, etc. Getting tired of the M46 and the need to do something to it at least every year or two. I also found parts to swap to an M47 but those have the same extra short 1st gear ratio as the M46 and are known for being more fragile, although I doubt I would break one the way I use the car. The T5 swaps are appealing and they have better ratio spacing but everyone seems to have problems getting the shifter area to seal up well and positioning the shift lever without cutting up the floor, plus they are pretty noisy. And for the cost of the adapter and machining and driveline work, plus a decent used T5 trans, the price difference in the end is minimal. So, going with the M90 that bolts right in and has better ratio spacing is a route I am considering.

Here are the specific questions I have:

- Did everything work out OK with the rear transmission mount and its crossmember? Would you be able to post some pictures of how the late style mount bolted up to the early car you have, and what the canted front motor mounts look like now with everything installed? You didn't have to swap to the late style vertical motor mounts and brackets, right?

- Did you need to change to a hydraulic clutch pedal, or were you able to continue with a cable operated clutch somehow?

- It sounds like you kept the original dog dish type solid flywheel that had been used with the old M46 and that worked fine with the M90? Is the clutch disk different, different input shaft splines etc? Or could an M46/47 type friction disk work also with an M90? M90 specific parts might be tough to source here.

- Are you happy with the shift quality, gear ratio spacing, and noise level of the gearbox? How would you compare it to the M46 you took out?

Thanks in advance for any more you can share.

[barkster1971]

There's no cabled operated clutch on a 760. Maybe on an old 240. As the floor pan and dimensions are the same as a 940 (which had the M90) everything bolts on. Don't have to mess about with engine mounts. M46 is old tech and a lot more agricultural than the M90. The gear ratios are a lot better too, I did put new gearbox oil in it. No more noise than the old one, but I miss the UP arrow in green on the dash.

[v8volvo]

Thanks for the reply and info.

Interesting your point about the cable clutch. It took me a minute to realize that that difference there is probably due to RHD/LHD variation. The LHD diesel models here, all of them (240/260 and 740/760), did have cable operated clutches. Non turbo 700 series gas cars had cable clutches too. Only the turbo gas and 16 valve gas 700 series models got hydraulic clutches here. By contrast it sounds like RHD UK cars never had cable clutches in the 700 series at all and used hydraulic action across the board.

Makes sense since running a cable from the right hand side of the firewall all the way around to the left hand side of the bellhousing probably would have been difficult, easier to use hydraulic tubing and cylinders on an RHD car.

So in short, converting from cable to hydraulic clutch is an extra step I would need to do with my 760, whereas you fortunately didn't have to worry about it.

Glad to hear you are liking it. I'm thinking about it. I guess I would need to round up a 740 Turbo clutch master cylinder and pressure line and pedal. That would be annoying, since I threw a whole set of those exact parts away a few years ago, that I removed from a turbo gas 745 I converted to turbo diesel (now owned by member RedArrow here) and had to swap the original hydraulic system to the diesel cable setup. Guess I should have kept them.