Who Is Running A SM420 Behind A Dauntless ?

I would point out that the Tera Low gears are expensive (maybe you want to spend the money on something else?) and supposedly are noisy. Being noisy is saying something, because the Dana 18 is pretty noisy already without the extra-noisy gears.

 

The 465 case is larger top to bottom, front to back and generally bulkier than the 420 case. The u-joint interference with a Dana 18 mounted on the 420 is a result of the pronounced bulge on the passenger side of the case to house the reverse gear. Other than this bulge, the 420 is slightly smaller and lighter than the 465. Both are excellent transmissions. The 465 has advantages over the 420 that have already been discussed in this thread: parts availability and slightly more modern shifting mannerisms.

Here's a pic showing the SM420 bulge

 

I have a 420/18/OD behind a 4.1L even fire Buick V6 in my Flattie. LOVE IT. While the 7 to 1 first gear is great, the second gear is also of benefit in that it is a little slower than the other transmissions that are normally used behind the V6. T90's are either a 2.79 or a 3.34 first. The T14 is a 3.1 first. T18's are a 3.09. The 420 is, according to Novak, a 3.6 (other sources list it as a 3.54) second gear which is what you normally start out in on the street. I should also mention the 465 is essentially the same as the 420 at 3.58. People tend to swap truck 4 speeds in their Jeeps for the strength and the crawlability (is that a word?) afforded by the granny gear, but the 420 and 465's lower 2nd gears offer a greater benefit even on the street.
If you do the swap be prepared to modify and or relocate the crossmember, floorpan, driveshafts, and clutch linkage. Sounds like a lot but you only have to do it once. I've never heard of anyone taking a truck 4 speed out and going back to a 3 speed.
Keep us posted on your progress.

FWIW,
Mike

 

Correction-
The optional Jeep T18 was a 4 to 1 first gear. A Ford T18 swap had a 6.32 first and a 3.09 second gear.
Note to self- Improve late night proofreading skills...

Mike

 

You guys are giving a lot of great info. I appreciate it a lot. I'm just about done washing the gremlins out of the 2a and then this is getting started. I have two very nice 62 cj5's to work with and should need nothing. I also have a 66 with a dauntless motor mounts to remove. All in all, there is tub work to do, some axle preferences to review and we will be getting started. well, I will be starting on the tub work pretty soon. I also have the bug for a 66-71 Jeepster, iffin your knowing someone that wants to part with one.

 

I'm also looking at adding a few inches to the wheel base and or frame of an early cj5 to get me where I want to be with this. I added a few inches to my cj2a, for the same reasons.

 

I looked this morning and did not see where the u-joints has any problem at all with clearance. Was this only an issue with the later 420 with the webbing added. Mine is the first generation without any webs.

 

In most situations the old style 420 will not interfere.

 

I run a sm420 in both my 55 and 71 behind a 225 v6. Great transmission if you want to have a super low gear for crawling. Running an Atlas and kluneV in the 55 with no clearance issues. My 71 is the military sm420 with a solid case and need to do some grinding on the case to clear the front u-joint.

 

I'm thinking 488's with the 7/1 first with a Dana 18 will give me a pretty good crawl. Whats the math on that, I have to look up the 18 low gearing.

 

7x2.42x4.88=83

 

I was figuring around 85, but that sounds correct to me.

 

The stock gears right now are 538 with a trak-lok rear end. I think that puts me around 91.**** crawl ratio. I may start off with the 538's for now and wait until I get a flanged Dana 44 to go higher. The axle is already rebuilt. I'm heading into this project in a couple of weeks and just trying to firm up my selections. I did get the shifting tower problem straightened out. Just had to align the dogs.