sm420

Well, I got a SM420 at the junkyard some time back. Pulled it out of a 60 something chevy p/u. Anyways, I also got the bellhousing and flywheel too. Now, I just wanted to verify something. The Buick bellhousing patern and Chevy bellhousing pattern are different, right? Also, can I use the flywheel I pulled with a 231 or do I need something different?

 

Bellhousing on a Chevy motor is different than the Buick and so is the flywheel, both unusable on the Buick motor.

 

Darn, Darn, and DARN again. Hmmm.. more stuff to buy. Thus why I call my jeep the damoneypit. Oh well. Having fun doing it anyways.

 

If you are using an odd fire 225 you'll have to use an odd fire flywheel. I thought Chevy and Buick bellhousings had the same bolt pattern. Could be wrong. It's happpened before. The 420 is a great tranny. My business partner runs one in his '70 CJ. He used an adapter from Novak Ent. to mount it to the transfer case but I believe it bolted right up to the Buick bellhousing. http://www.novak-adapt.com/

 

I have not actually done this, but the tranny will bolt up to the buick bell, the bottom bolt holes have to be drilled out and trans has to be bolted to the bell. Other than that I am told the stock clutch will work. Hooking it to your TC could be interesting.... I think you end up with a spud shaft in a adapter.
it is worth the effort and expense to get that wicked low first!!!

-Hill

 

Not to mention, its the most over engineered transmissions ever made. Think 1947, thats when they were first put into production. Think 2 ton dump trucks with a full load. Not a single piece of aluminum, no plastic trust washers, or peanut gears on a 3/4" main shaft.
I am a big fan of 420s. After 150k miles, you can clean them up, put in new bearings and gaskets and they are more than up to the task of an old, lightweight jeep.
One of the biggest advantages of putting one in is that if you stall on a hill, in 4 wheel low, you just put it in first and hit the starter. It will walk up the hill untill the engine fires with no stress on the starter, clutch or anything.
With a stock model 18 T-case it equals something like 70:1 with mild 3:73 gears.

 

I have done it and the SM 420 bolts right up to the Buick bellhousing...you just have to drill the threads out of the lower two holes in the bellhousing (cause the SM is threaded too) and run two new grade 8 bolts back into the tranny from inside the housing. You do need an adapter kit from either Advance or Novak and there are more parts involved in the kit and you also need a new sealed rear bearing for the tranny and a bearing locator with a hollowed out center hole to tie the tranny to the D18. You'll also have to fab a new crossmember and clutch control(hydralic w/ hanging pedals works great). The whole tranny/transfer case assembly moves to the rear 4"..need shorter rear and longer front driveshafts. The rewards are great. ..granny low gear and syncrowed(sp?) second gear.

 

Re the Chevy-BOP adapter plates (can be purchased from Summit for ca $50), the consensus is that they are junk. Don't use one.

No personal experience - just what I've been told.

 

Just a few quick thoughts. I did the sm465 conversion last year. The Chevy and Buick bolt patterns are indeed different. You will need a Buick/Olds/Pontiac bell housing. They can be found pretty inexpensivley on EBay or at junkyards. One thing I had to do on the BH was have the opening for the transmission machined and opened up a little. There is a great article on it here somewhere. I'll see if I can find the link. I used the Novak kit and was very impressed with the qulaity and customer service. This is the second best project I have ever done on my 71', first being the Detroit locker in the rear.

 

The 420 is awesome. I used the Rube adapter on mine. Kit comes with everything you need for $400. Also went with the hanging pedals/ hyd. clutch set-up.

 

do you have a url on the rube adapter?