Dont forget pilot brg.

I did the M410 conversion from BW35 on a '68 144 many years ago.
Most has been already said, but the two things that need to be paid attention to are, don't even try to remove the bellhousing from the M410, you will need to re-shim the input shaft bearings and replace seals that are not readily available, and the trans will leak profusely. It is not like an M41 at all.
You will regret putting the small rear flange on the M410 with old small driveshaft. Get the front 1/2 of an M46 or one from the 1800 where the M410 came from, along with the larger flange. That small u-joint will get eaten up in short time with the manual trans. If you can, go with the bigger driveshaft all the way to the diff.
As said the torque converter bolts need to be removed before you take the auto box out.

I'm probably picking up an M410 on Saturday for my '72 145 to do the same conversion you're doing, so I'm intensely interested in how everything is shaping up.

Mainly - Did you find a smaller output flange? Or a larger flanged driveshaft?

Was the BW35 frontshaft the right length?

As Goatman suggested--you need to remove the four torque converter to flex plate bolts. Take the dip stick tube out (drain the oil first, of course) before dropping the auto. The transmission will separate from the bellhousing with the six 5/16 bolts (these often loosen up and are worth checking for tightness for folks still running the BW35) but I'd pull the whole unit together. You can replace the rear seal housing with one from a B21-B230 made for the neoprene seal but remember to get the pan bolts for it too (metric--I paint those two so as to not mix them up). -- Dave

I usually loosen or remove the top bell housing bolts before I tilt the engine.
With a BW35, the bell housing will come off with the transmission. In a manual transmission equipped car, you would remove the transmission from the bell housing and then the bell housing from the engine.
Not sure how easy it will be for you to fit the M410 to the B18 with the engine remaining in the car considering you have to install it with the bell housing connected to the gearbox. Hmmm, never done that before. I'm sure it would be easy if the engine / transmission were out of the car and could go in as one piece.

You shouldn't have to remove the fan if you unbolt the radiator and have it tilt as the engine tilts.

You may be able to get an output flange from Don Thibult. He has had J-type to small flanges in the past. Not sure if a M410 to small was ever available though.

Yes, replace the rear main seal while you're in there. You may want to consider an update to a neoprene seal. Your existing rear main seal housing which accepts a felt seal can be machined to accept a neoprene seal. I have had good results with both felt or neoprene seals. Having said that, I have updated to the neoprene when possible.
--
'60 PV544, '68 220, '70 145, '86 745T

Drop the engine a bit,but not so much that it pinches the heater hoses on the firewall.
Take 2 or 3 feet of 1/2" extensions,and get the top bell housing bolts first.
Remove the rest of the bell housing bolts.
Wiggle the transmission and pull it off.
Remove the lower engine cover to get at the torque converter to ring gear bolts.
These bolts will be shorter than flywheel bolts.....
You have the smaller drive shaft in a pre 1970 140.
A complete later driveshaft,& larger center support retaining bracket would be best.
The BW 35 & M41 use the same short shaft length,IDK about the M 410.
--
71-145-S

Sounds like you're well on your way. I've done this same task two years ago. One tool which made the process easier was to use a motorcycle lift to lower and raise the transmission.

When I pulled mine, I removed all the bell housing bolts and took the tranny and bell housing off as one unit. Don't forget to disconnect the wires that are on the drivers side.

Jack

I'm no expert on this but:


You MUST remove the torque-converter to flex-plate fasteners before continuing!


Goatman