sm420 thoughts...

[FINOCJ]

A connection through the ecj5 forum has an a 1966 sm420 for sale....its a truck 4speed with 7:1 granny 1st. It a fairly common swap for jeep 3 speeds (most with about a 3.1:1 1st) - in my case replacing a T14. The T18 and sm465 are also common 4speed swaps - each has it benefits and drawbacks - but sm420 and t18 are preferable to me. The cost of the transmission is pretty small - but Novak adapter for the D18 transfer case is not cheap - but will work seamlessly with my D18 tera lows. Plus I would need to rework the removable access floorpans as well as pay for driveshaft modification. Some people say they can do the swap for $1k but most realistically say $1500+ when all is said and done (like rebuild kit for the transmission). I am thinking I can possibly do it for $1200 as I have already done some other drivetrain work - and the sm420 has the least fiddling with clutch, pilot bearing and so forth stuff. I really want to install a locker next on my jeep....I think its most useful. Thinking of buying this sm420 and storing it away for a couple years while doing some other stuff. But then again, do I really want to start modifying floorpans and driveshafts....do I really need a granny 1st? hmmm....

[Jim]

You say it's a low cost item. It shouldn't take too much room to store. Buy it. Store it.

Do the locker and wheel for a year.

Then decide if the 420 is something to install - or not and sell it off - likely being a wash in the buy/sell funds.

<edited>

[Spieg]

Not an expert on the SM420, but will say that a granny gear/truck transmission is really nice to have (with Terra-low, you'll almost be able to get out and check your tire pressure on the move). Going from a 3 speed, you won't notice much difference on the road.

I've recently been attracted to the idea of an AX15 over my T18 (overdrive would sure make life easier for the engine on those 500 mile cannon-ball trips).

[FINOCJ]

Fortunately, with my Warn overdrive, my 3 speed really is a 6 speed with OD. I would be able to keep the same overdrive functionality with the 4 speed (it would have 8 forward gears). With a granny 1st, the Tera-lows aren't really needed - or at least you are in the range of diminishing returns. When I installed Tera-lows, a number of people said just to skip them and put in a 4speed - but I kind of like the more original aspect. The Tera-lows give me just enough crawl ratio as is, but it would be nice to have more.
My current gear ratios in low range:
1st:47.7
1stOD: 38.1
2nd: 24.7
2ndOD: 19.8
3rd: 15.3
3rdOD: 12.3

Theoretical ratios with sm420 - probably a bit overkill but:
1st: 107.6
1stOD: 86.1
2nd: 55.3
2ndOD: 44.3
3rd: 26.1
3rdOD: 20.9
4th: 15.3
4thOD: 12.3


Here are some pics of the 1966 sm420 - its a 3rd gen which is the final and strongest case and best civilian design (there was a 4th gen for the military I believe). It could only be better if it was a 1967 model with a back-up light switch, but thinking I could figure something out:

[FINOCJ]

Jim previously posted:

[Jim]

Where - anywhere someone here travels for a shuffle? I drive to Illinois 4x per year...

Put out a feeler and see if anyone else has travels and open trunk space to save transport?

[Java]

At that price I'd buy it regardless. they're not making any more of them, and it looks like a pressure washer could double the value right away, you won't lose on it. I'd lock the rear first; I put a T18a into my last jeep, a YJ crawler, to replace the BA10/5. I put it in before I swapped out the D35 and with an open rear it was not too useful, couldn't rev up enough to combat wheel slip without going to 2nd. I swapped the rear for a Detroit Locked Scout 44 and it all came together. I did MSV/CF in 4hi / 1st gear without realizing it. Also made changing tire size easy, no further regearing required.

[ColoJeeper]

Out of curiosity, have you looked at or considered the NP435 transmission? Also has a 6.69 granny first gear. Put one of these into my CJ-7 and have been totally happy with it. I think the total cost was about $1500 using the Novak adapter and a custom machined thow-out bearing. This coupled with a Dana 300 TC and 4.27 gears in the axles gave me a 75.1 crawl ratio in low range first gear.

[FINOCJ]

Np435 can be done but for some reason that I don't know, it hasn't been very common on early cjs. Maybe it wasn't as common back in the day as the transmission was developed more recently? Looks like a good 4speed - not sure of its differences with the T18. I think its pretty similar a swap as the T18 as both are common ford applications. The advantage of the gm transmissions (sm420/465) is they are direct bolt on to the BOP bellhousing and use the same clutch set-up as came with the jeep v6 (all buick stuff). Modifying a BOP bellhousing for a T18 or np435 isn't too hard - it doesn't require an adapter (which is good to save overall length) - but does add some extra hassle with some modified custom clutch parts and transmission input retainer. The amc cj t18 from 76-79 or so is often considered the best swap option as it is the shortest option mating directly to a D18/20 without adapter. Everything else is a bit longer with adapters to D18 and they all come out about the same (the sm420 is shorter but has longer adapter, t18 is longer but with shorter adapter etc). I haven't looked for an np435 so don't really know if they are common and can be found at a good price....

[ColoJeeper]

I always forget the differences with the earlier CJ's and that you are running a GM motor. The T5 bellhousing in the later CJ's bolted up to the NP435 so made that easy. I do think on the CJ that if I were to do it again, I would have gone with an automatic transmission instead. Unfortunately for me, the CJ now just sits as garage art and takes up space. Not sure what I want to do with it since the JKU Rubicon has all the same capabilities of the CJ and offers a much more comfortable ride at the same time. Know anybody that wants a project CJ-7 with some nice old school parts on it?

[FINOCJ]

I am always interested in old cjs! 86 would have a D44 rear? 4speed is nice. locked? 258?

[ColoJeeper]

Dana 30 front axle with lockrite locker
Dana 44 rear axle with Detroit locker
Sun Performance rocker guards
Ramsey Pro 9000 winch
258-6 engine with around 260,000 miles on it
4" BDS springs w/front shackle reverse
rancho 9000 adjustable shocks
frame cracked and repaired several times
body fairly solid but rust around wheel wells and a little in the floorpans
Off Yor Rocker diamond plate steel rear corners

Like I say...lots of old school parts.

[FINOCJ]

If that is running and driving i bet it would sell quite nicely...I am always interested in old cj for the right price. I think the wide-track cj7s hit upon a pretty sweet combination of wheelbase and track width - sometime really wish I would have kept my 84cj7 as it was quite luxurious compared to an ecj5. The aftermarket support for cj7s is also still quite abundant. If you do think you want to move it along i am always interested to take a look as you have the good stuff in terms of driveline with D30/44 and NP435/D300.

[FINOCJ]

As you can see in the pics posted above, there is a bit of rust on some of the teeth...how would you all go about cleaning that up....use a polishing pad by hand and clean each tooth up a bit?