I am changing out my Muncie 4 speed (car tranny). No more sand dune and drag activitys!!! I have a SM420 and will buy an adapter. I am curious .....Novak advertises that there adapter will allow use of the standard output yoke to front axle out of the T-20 transfercase also no grinding of tranny webs is required. Novak also claims to be a heat treated shaft and apparently Advanced isnot........I can agree with this claim since my current Muncie Advanced Mainshaft had worn on the nose ( where needles run inside of input shaft) and I had to turn it down( Machinist by trade) and shrink on a hardened sleeve that has held up well.... Does anyone have a history of preference with the Sm420 swap?????
I fully understand the procedure for swapping in this tranny
IE: mounting lower 2 bolts to tranny from INSIDE of bellhousing and it seems that the adapters available for this tranny are all very close to my current tran- adapter length combo so if I luck out drivelines may stay there present length.....

Any input will be greatly appreciated. Also does anyone know of rebuild text available on-line for the SM420??????

Thank you.

Did a search and found this, http://www.kinzers.com/don/landcrui...20/doc/300x300/
Do a search on this BB there is a lot of good info on the 420.
This result may have some good info in it. http://www.pirate4x4.com/forum/showthread.php?s=&threadid=25829&highlight=sm+420+manual
Downloaded the 420 manual with a the zip file, worked good for me. Easier to see than opening the pics.
Hope this helps, I like these tranys also. Just bought a 67 with the reverse light switch today. A good find for me. Andy

Thanks for the reply and info!!!!! The Sm420 that I recently purchased is brand new in the box made for military contract olive drab paint and military lubrication tag attatched...A brand spanking new SM 420!!!!! :rolleyes: :cool: :eek: :emb: :emb:

WOW :eek: ...sweet a brand new sm420....your a lucky man.
:cool:

Well I did the very same swap and used the Novak adapter....

I had a car muncie/advanced adapter to a spicer 18 t- case and swapped a sm420 with a Novac adapter to the same spicer 18 t-case. I ran a buick 225.

Novacs adapter is nice with the hardened stub shaft but I ran into three problems.

1. one of the bolt holes didn't line up exactly...no biggy I just oversized that hole.
2. one hole was threaded that didn't need to be threaded...no biggy I just removed the threads.
3. I installed it and ran it only to find out that my gears would grind in fourth gear...I thought that maybe my sincro's were worn since I used an old set that seemed to be in good condition.
I ripped it all a part and found that the adapter (that is also the rear main shaft bearing retainer) was machined a few thousands too deep and the Gear stack would move creating excess end play at the fourth gear sincro(fourth gear is on the input shaft).

I called Eric at Novac and told him about the problem so he checked into it and sent me another housing.
In the mean time I put the old one back in and filled the gap with JB weld(didn't want to wait) and it ran just fine. This way I could put the new one on the shelf and get a better resale value.

I've since sold the adapter for $350 and kept the old housing for some reason ...now I run an atlas II with an advanced D300 adapter and I am not impressed with the stub shaft...for the money you would think they could harden that thing.
I did learn however, that advanced has a locking collar for retaining the rear bearing onto the shaft and is included in their kits.
This comes in handy because with out it you'll have to remove the man shaft and machine a c clip groove to keep the main shaft from moving inward screwing up your sincro tolerance(main shaft end play).
With the Novac kit I didn't get this collar (they may have one by now)and I couldn't machine the hardened shaft on my little lathe (Just made a shiny spot) so I used a retaining compound that locite makes (part#609) this still holds today though it will be interesting to remove some day.

-Kerry

I BTW had to lengthen the front drive shaft , shorten the rear and modify the cross member for the tourque mount on the t-case to make this swap work.
On a spicer 18 (offset Rear yoke)this mount is important.
-Kerry