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?