SM420 tranny......
 

Looking for information..... and /or real experience...

Considering fitting a SM420 fully synchro to a CMP bell housing....at first glance one bolt of the four bolts seems out of place.....

Yet I know it was done...... Luc Jette in Montreal has a 4 speed synchro in his C15a....... he is South sunning himself...... who else has knowledge of how this is done......

Can you help!!!!!

Bob C.

Interested to learn more about this swap...

PS: here is another restoration by Louis Skebo: http://www.mapleleafup.net/forums/sh...ighlight=sm420

Sm420
 

Another thread

http://www.mapleleafup.net/forums/sh...ad.php?t=14363

First prize goes to Paul.......
 

Good show Paul you found what I couldn't find......

Posting was also noticed by Luc Jette from Montreal who contacted me tonite.

He did a similar conversion and still drives the old C15a..... Once the bell housing is modified as documented by Phil W. it is a simple bolt on back in place...... just remember that the short drive shaft linking to the T case has to be shortened by about an inch......

For safety it is best to use Blue Loctite tight on the u joint nuts/bolts near the rear of the tranny....if they work loose they will shear off most of the bolts and shatter the rear tranny cover like a buzz saw...... Blue Loctite can be softened with a propane torch if you need to remove them at a later date.

Now the hunt is on to find in .... the barn, somewhere, to locate the original 1959 Chev bell housing that came with my 261...... to try that trick as I have a complete SM 420 sitting on the floor of the shed doing nuttin'.

The Forum does work......... thanks everyone...... if this really works we no longer have to keep our 216 original RH drive bell housing under lock and key.

Hummmm..... I may have some spare old bell housing to practice on courtesy of Paul.......who also gets second prize for the spare parts...

Bellhousing
 

Hi Bob, I think that a 1948 to 1952 bellhousing is what you would need. The rear engine mounts changed in 1953 and won’t fit the crossmember in your truck. The bellhousing from 1948 up to 52 will fit the sm420 transmission and shouldn’t be too hard to find.

Paul

Found one.....
 

...pure luck as parts from Eastern Township.....thanks Paul

Apparently came from a deluxe Chev car or could have been a 1/2 ton truck

Said bell housing has the large hole for the input shaft, the off set screws on the sheet metal inspection late and the bolt pattern of the SM420.....but was bolted to a 3 speed....... long side shifter with long one pice casting ending in the flange to bolt on the enclosed drive shaft..... buyer is working on a 42 CMP trying to fita 235 and the SM420.

The bell housing has been received and close up photo shows the casting to be"bilingual'..... it has the factory left hand drive clutch window but on the right is the outline of a wooden plug with screwheads casted exactly where he will have to cut a RH clutch fork window.....inside there is a large bulge in the casting exactly where the fulcrum bolt will need to be installed on the RH side..... drilled to 7/16 fine thread.

....and the side of the bell housing is meant to take the 90 degree angle military bracket so it will bolt right up to the CMP cross member...

Key words.....1948 to 1952 Chev 6 cylinder bell housing......

Bellhousing
 

Hi Bob, the bellhousing that you are describing is from a pickup truck. The car bellhousing has a small bolt pattern for the transmission in those years. The car transmission is quite a bit smaller than the truck three speed. The cars didn’t get the same transmission bolt pattern until 1955 along with the open drive shaft.

Thanks Paul......
 

....so much to remember!!!!