M41 Conversion in a 1967 122 Wagon w/ Short Shifter: Anyone Been Down this Road?

[polaris]

Currently assisting a friend of mine on retrofitting a P1800 short-shift M-41 w/ d-type OD (or would that be M-41D?) into his 1967 122S wagon. Looking to get any experienced-related advice or input from someone who has done this retrofit before.


Backstory:
Two and a half years ago I was tipped off about this wagon and finally landed it in Feb 2022. Started a project thread on the car (Latest Round Fender Acquisition: 1967 122s Wagon) Lost steam/motivation on posting about it due to several posts about it vaporizing during the great TB blackout of April-May 2022. By the time TB finally came back on-line, my friend had made me an offer on the project and it was transitioning to him.

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Since the B18 engine in the wagon was belching smoke like a teenager with a new vape pen, was able to find someone selling a B18, M41, driveshaft, and hub-to-hub rear axle here in SF. He had harvested these from a crashed P1800 as spares for his 1965 P1800. He acquired the donor car 15+ years ago and finally decided they were done storing these parts and wanted their garage space back. While progress has been slow on this project, progress is being made. Removed the old engine and M40 out of the wagon. Test fit the M-41 with the short shifter to confirm our suspicions it would not fit into the tunnel. Installed the new engine with the M40 and got it to run for a couple minutes. The water pump leaked from the top seals (most likely from sitting so long,) stopped everything to replace that out. While the transmission tunnel from an 1800 would be the perfect transplant for the short shifter set up, that would be quite the effort to source/find. In the middle of April, a 142E (BW35) dropped at the Oakland Pick-n-Pull. Went over with a sawzall and were able to bring that transmission tunnel back to SF. The M40 was removed out of the 122 wagon as well as the front seats and carpets to prep for retrofitting the new tunnel.

Looking for Feedback, Voice(s) of Experience:
Arriving at the point to start cutting out the old transmission tunnel. The plan of attack is to first cut the tunnel around the top of the tunnel (see Sharpie marks in the 3rd & 4th picture) going from the forward, long-shifter opened, along the side and just into where the driveshaft tunnel begins. The blue painters tape marks the perimeter of the 142 donor tunnel cap. After the top piece is cut out of the 122, install the M41 and trim/adjust where needed on the existing tunnel and 142 cover piece.

Any thoughts, words of advice/wisdom or related experiences worth sharing to know before cutting into the 122 tunnel?

 

[James M]

Jack has been through this exact swap, might be covered on his 66 Amazon coupe build thread

 

[JohnMc]

Lol, I did a similar but more primitive version of this, I put a 122 tunnel in my PV to make room for an M41. Basically the part you'll be cutting out of yours.

 

[planetman]

We've done several of theses.

FYI, it's best to use a tunnel section from a 1962-1969 P1800S if you want to use the P1800S transmission shift cover that came on your M41 and those can be hard to find.

I suggest you use a shift cover from a 1972-1974 140 or 1969-1975 164 or a 1975 240 along with a new tunnel section that we happen to have in stock. You can use a shift cover from a 1970-1973 1800E/ES, but you will probably want the shifter handle from 1 of the above as the 1800E/ES shifter has a sharper bend and it's a little uncomfortable to use.

BTW, any reason you can't just use the original M40 shift cover and shifter?

 

[polaris]

Jack has been through this exact swap, might be covered on his 66 Amazon coupe build thread

Thank you for pointing to Jack's thread. I had gone through the first 5 or so pages of posts but hadn't made it to his post where he shared a picture of a modified tunnel. Utilized the TB search functionality using terms like "122" "tunnel" "short shift" "M41" but was coming up empty.

We've done several of theses.

FYI, it's best to use a tunnel section from a 1962-1969 P1800S if you want to use the P1800S transmission shift cover that came on your M41 and those can be hard to find.

I suggest you use a shift cover from a 1972-1974 140 or 1969-1975 164 or a 1975 240 along with a new tunnel section that we happen to have in stock. You can use a shift cover from a 1970-1973 1800E/ES, but you will probably want the shifter handle from 1 of the above as the 1800E/ES shifter has a sharper bend and it's a little uncomfortable to use.

BTW, any reason you can't just use the original M40 shift cover and shifter?

Appreciate the expert advice and I will pass on your recommendations for the optimal shifter. The tunnel will be modified regardless, once other suitable/better donor parts are found, swap those out accordingly.

I have suggested using the M40's long-throw shifter several times. My friend really wants to have a similar shifter set up to what is in his 1972 1800ES. When the 142 showed up at the boneyard, it pretty much sealed the decision to modify the tunnel.

 

[hiperfauto]

The early 1800 shift cover (top) is longer than the later 140/1800E covers. You won't be able to swap a late cover on without relocating the tunnel so the shifter hole lines up.


This has the late shift cover with a 240 tunnel.

 

[Jack]

oh Im being referenced!

it only took me 4 years to replace my clunky m41

what surprised me was how little of the donor tunnel you actually need. Worth the swap as the original covers get messed up ....
skandix was doing an exchange for a little bit but it looks to be NLA https://www.skandix.de/en/spare-par...repair/cover-gearbox-housing-m30-m40/1045094/

I think it was like $500 to get that done!

and before someone says "use a larger pin" thats cool dude but only a temp solution and not the best IMO


ps is that a 914 i spy?

 

[polaris]

The early 1800 shift cover (top) is longer than the later 140/1800E covers. You won't be able to swap a late cover on without relocating the tunnel so the shifter hole lines up.
View attachment 22178

Thank you for that picture comparing the shifter covers. I was under the false assumption they were all the same length, or more like I did not think about them being different at all.

it only took me 4 years to replace my clunky m41

what surprised me was how little of the donor tunnel you actually need. Worth the swap as the original covers get messed up ....
skandix was doing an exchange for a little bit but it looks to be NLA https://www.skandix.de/en/spare-par...repair/cover-gearbox-housing-m30-m40/1045094/

When I saw the picture in your post with the tunnel cut, that was my thinking as well of how little was needed to be removed from the 122 tunnel. Estimated more needed to be removed than what you had done.

ps is that a 914 i spy?

Yes, a 914 with a Subaru 2.5L transplant in the back, currently a work in progress. That is owned by another person sharing the warehouse space.

Right now there are three 1967 122s residing there; a sedan, the wagon and a 123GT. The sedan has been a frequent reference while working on the wagon.

 

[polaris]

Update and Driveshaft Question

With Jack's image as a reference, the transmission tunnel cut lines were redrawn. Temporarily installed the front drivers seat to check the placement and fitment between the shifter and the seat cusions. The clearances did not seem to be an issue giving the green light to cut the the top of the 122's tunnel out. After the surgery, the next couple hours were spent attempting to get the M41 attached to the back of the engine with no success. The angle firewall kept on interfering the ears on the bellhousing. After several tries to get the transmission mated it was time to think of a new approach.

The next day decoupled all connections to the engine. Using a cherry picker, raised the engine upwards from the front to change the access angle for the M41. Two hydraulic jacks were utilized to raise transmission and guide the input shaft in through the clutch plate. After some wiggling and persuasion, we were able finally able to get the transmission's splines matched and bolts threaded into the engine block. Dropped the engine down back onto the engine mounts. Once the transmission was secured by the cross member, removed the jack out from under the M41 and started to hook everything back up to the engine.

Everything is sitting perfect with the overdrive, short-shifter set up and then came upon an issue with the driveshaft. As part of the B18/M41 deal, there was a driveshaft included. When bringing it under the car to install this part, it is readily apparent it is not long enough for this 122 wagon. The distance from the output flange on the M41 to the pinion flange is 52.5". The driveshaft (presumably from an 1800S) provided by the PO is 46" long (the original M40 driveshaft from the 122 wagon is 63.5" long.)

Question:
Does the M40 driveshaft need to be taken to shop to be shortened or is there another specific part/driveshaft which needs to be used for this application?

.

 

[OttoB]

I'd visit a driveshaft shop and ask for shortening, new joints and balancing.

In your picture there is two different style of support bearings. Attachment points at floor are completely different.

Or...

Shorten Your Driveshaft:

Here is a pictorial on how to shorten your driveshaft. You may need to shorten your driveshaft because of a tranny change, rear end change or in my...

www.jalopyjournal.com

 

[James M]

Is the longer shaft the existing M40 one? If so it's got a type 3 driveshaft & center support bearing

 

[Harry Tuttle]

I suppose if you ran across a driveshaft half from an auto trans car there may be a chance it would be the right length. No doubt Hiperfauto could answer that question directly.

Looks like you put the tranny in with the bell housing attached. Do yourself a favor next time and put the bell on the engine first, then put the tranny in.

 

[hiperfauto]

I suppose if you ran across a driveshaft half from an auto trans car there may be a chance it would be the right length. No doubt Hiperfauto could answer that question directly.

Give the man a cigar! BW35 and M41 driveshafts are the same for the 120 series cars.

Looks like you put the tranny in with the bell housing attached. Do yourself a favor next time and put the bell on the engine first, then put the tranny in.

Ding ding ding. This is the way to do it.

 

[Harry Tuttle]

Give the man a cigar!

I am basking in the light of the master's approval, but it is not a stretch to predict that you would know the answer.

 

[JohnMc]

Give the man a cigar! BW35 and M41 driveshafts are the same for the 120 series cars.

IIRC they used a 'long tailed' version of the BW35.

Of course, other than having the same length as the M41, it was just as horrible as any other BW35.

 

[polaris]

Give the man a cigar! BW35 and M41 driveshafts are the same for the 120 series cars.

I had forgotten about the automatics in relation to appropriate length driveshaft. Looks like front section from a 140 automatic is another contender as well according to another TB posting from 2019.

Ding ding ding. This is the way to do it.

After reading Harry Tuttle and Hiperfauto's response on the proper installation method, I realized this is the first time I have removed/installed a transmission into a 122. Performed several clutch jobs/transmission removals on my 1800e, 140s, 240s and have had no issues with fitment or clearance.

During the initial attempt on the first day, my friend Alex and I discussed whether it was better to remove the body of the M41 off of the bell housing or unhook & tilt the engine. As you can see in the previous post the decision was to tilt the engine. This whole process has been educational to say the least. One of the reasons I have been helping my friend with this project is to learn how to do a retrofit like this on a 122.

Greatly appreciate all of the input/information with this upgrade project. It is one thing to read about it and another to actually do it and make it happen.