pre sm-420 tranny

Anyone ever hear of putting an old, 1936-1948, chevy 4 speed tranny into a cj with the buick v6 ? it has no synchro gears, but has 7:31 to 1 first gear. I have one of these and was wondering if any of the sm-420 adapter kits might fit, or if this is a totally different animal.

 

There is a few guys here running that transmission.

 

How are you at double clutching?

 

You don't have to double-clutch on the upshifts if you time them right.

Still, building with a crashbox when you don't have to seems kind of dumb (sorry), even if you have the transmission. SM420s and 465s are cheap and widely available. Spending those (comparatively few) extra dollars to get synchromesh is a no-brainer.

 

you don't have to use the clutch for downshifting, either. just takes practice.

 

1st gear is listed as 7.06:1 not 7.31:1. Is this the transmission you refer to?

If so I would think it not feasible just based on the pictures, it has similarities compared to the sm420 but also has alot of differences. I personally wouldn't want a crashbox in a jeep I intend to drive in the woods, The double clutching and timing the shifts work great on the street but would quickly destroy the transmission on the trails and parts for this thing would be almost impossbile to find and afford. An sm420 can be had for aroun $100 and its beter suited for the job.

 

From someone who has driven unsinchronized truck transmissions off road. Not like you might think, but but hauling hay, watermelons etc. in work trucks in the years past. I would think you widwest farm boys can relate to this. You generally do learn to double clutch these things as to reduce gear clash. I would add that these can be chalenge at best if you do any driving in mud where you want to "rock" the vehicle one if forward motion slows or stops. A major concern for me anyway would be a source for availability for parts. I have a 420 from the late fifties that I've saved back over the years because of this. The 465 so much more plentiful and cheap to buy.

 

thanks for the info, I guess I will look for an sm420 or sm465. BTW that gear ratio was 7.06 not 7.31, don't know where that # came from.