M40 Transmission?

Hi All,

I recently purchased a '64 122s. It came with a separate overdrive transmission. The stamping on the trans is:

380100
M350
K9

Does anyone know what type of transmission this is? M40? M41?

Will it bolt up to a B18 easily?

Thanks.
Dave (Toronto, Canada)

Is that the part number stamped on the plate that is riveted to the bottom of the 4 speed section near the transmission mount holes?

If it is an M41, then yes it will fit, but you will need a shorter driveshaft and some other ancillary parts to make it work.

It's stamped on the side of the transmission, not on the plate.

I'm pretty sure that is the part number for the transmission case.

The part number for the transmission assembly is stamped into the plate I mentioned.

Post a picture. It's worth a thousand words.

If you ever drive at highway speed for long periods of time, an OD gear is REALLY nice to have.

How do I add photos to the thread?

I use https://postimages.org/

They might work better as a link:
https://photos.app.goo.gl/ZLAzJvIbdO6MXDOs2
https://photos.app.goo.gl/PX5QKXau9y1uZxwg2
https://photos.app.goo.gl/Vf2JhQnxvbCxYD3X2
https://photos.app.goo.gl/X3RPAtLZFYhZbCti1

It's definitely an M41. M40 is the 4 speed version, no overdrive, all 4 speeds are contained inside the cast iron case. The M41 has the same (well, slight changes) transmission with 4 speeds and an electrically engaged OD hanging off the back end. A J-type is good - it's stronger than the very early M41 D type overdrives.

That has a remote 'short' shifter so it was either on a late 140 or any 1800. I don't have the details on how that transmission top/shifter extension changed over the years.

To put it in your 122 you would either need to modify the sheetmetal (use an 1800 tunnel or fabricate new) to accommodate the new shifter position, or swap on a 'long' shift lever trans cover. Drill and tap the 4th gear switch in the long shifter cover - running the OD in lower gears can be hard on it, and I understand that they are especially fragile in reverse, if you don't have that 4th gear switch you might eventually leave it engaged when you shouldn't.

You'll need a shorter front section of the driveshaft (when I put an M41 in my PV I had a driveline shop modify my existing one as M41 PV driveshafts are non-existant) and beware of the different flang sizes - Volvo used (at least) 3 different sizes, with only modest rhyme or pattern, over the M40/M41 production (across 3 models of cars).

And possibly some modest modification to the crossmember. And a longer speedometer cable (unless it has a fiddly and failure prone right angle drive).

Thank you very much JohnMC. This is some great information about the trans and how to install it. I've never installed a trans before but willing to give it a try. Any suggestions about clutch etc?

Clutch will be the same whether a M40 or M41.

A long shifter (like what it came with from the factory) would make things easier - assuming a stock 122.

What transmission is in the car now? If it had a manual transmission, it will be an easy install.

No reason for anything other than a stock clutch unless you've done *LOTS* of mods to the engine. My PV has about 170 hp (+/- some butt dyno calibration) and doesn't slip at all with a stock B20E clutch.

While you have it apart I'd ponder deep thoughts about:
- the ream main seal - you may have the original felt seal, which doesn't really stop oil from coming out as much as subtly attempt to discourage it from coming out. The seal housing can be machined to fit a later style (B21) neoprene seal - you could find one for sale or have a machine shop do it for you.
- The flywheel - if you want to take a little bit of the 'tractor' out of the engine, lightening the flywheel is a good start. I had a machine shop knock a few of the easiest pounds off mine for a very small amount of money (outside the clutch surface, didn't touch from there on in to the center) and it makes the engine feel a bit more zippy and responsive.

The wiring is fairly simple for the OD, it just needs switched 12V+ to one side of the 4th gear switch, out the other to one side of the OD solenoid, and a ground wire on the other side. The 122 had OD as a factory option, so you can (if you wanted) find a replacement turn signal switch housing with a spot for the OD switch. Or just rig up some other type of switch (I have a matching spare fan switch in the spot where the cig lighter used to be). Or rig up a cycling relay (like the headlight dimmer relay on a 240) hooked to the pull-back switch in the turn signal switch. Etc. It doesn't need a lot of current.

alschnertz said:

What transmission is in the car now? If it had a manual transmission, it will be an easy install.

Click to expand...

Good question. I don't believe any 122's had multiple threaded locations for trans support crossmembers. Also, the crossmember itself may have to be changed, even if there is an M40 in there now.

M40 and M41 will have the same mounting points.
I was wondering if the car had an automatic which would be a more difficult swap.

Edit due to moot questions

Automatics weren't offered in 122's until '65.

M40 and M41 use the same trans cross member, but the trans mount and bracket are different. The mount is stiffer and the bracket has the hole for the mount in a different location.

That looks like a late top cover 74? only with circlip shift stalk retention.

75 had a rubber isolator section built into the long top cover but was the same otherwise.

We have done dozens of M40 to M41 conversions on 122s and there are several ways to install the entire system.

So if you are interested, I can help you figure out which way to install it.

JohnMc said:

and I understand that they are especially fragile in reverse, if you don't have that 4th gear switch you might eventually leave it engaged when you shouldn't.

Click to expand...

Just to be clear, "fragile" means "will be destroyed if it is engaged and you let the clutch out in reverse". There's a one-way clutch in the OD that is used when it is engaged. The OD input cannot turn backwards and it just breaks everything up if you try. So yeah, the 4th gear lockout is a good idea.

http://volvoamazonpictures.se/guides/Overdrive in Volvo Amazon.pdf

The whole story is always better than drips and drabs...