There's a lever that moves the 1st/reverse gear that pivots down one side of the tranny. The top end of that lever also has to line up on the top cover when installing it. You need to be sure that the two forks AND the lever are lined up when installing the cover. Somebody posted a link here to a video of the SM420 a while back. I'll see if I can find that.

[on edit] the link is in this post. The lever and cover info appears at about 16 minutes in.

Last edited by klhansen; 11/30/2021 2:35 AM. Reason: added video link
Kevin
1951 Chevy 3100 work truck
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1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car)
Busting rust since the mid-60's
If you're smart enough to take it apart, you darn well better be smart enough to put it back together.