T.m.'s 4-speed Swap Thread.

I understand. I've spent quite alot of time debating between these 5 transmissions. Each has it's pros and cons.

If only the SM420s weren't all 57-77 years old, and they had better parts availability, it would be an easy choice for me.

 

Sm465 is a lot more work to fit behind a 225 due to the small index bellhousing.
A sm465 uses the same clutch as a t-90j so for me (chevy motor) it would be a very easy swap between those two. I'm not too familiar with the Buick paired transmissions but it is worlds easier when the clutch is the same or at least an option for some other application between a 225 and the 4 speed.

I've always thought of the t18 as the easiest fit for a 225. Another thing to consider is it might take months for the kit to show up if it is not in stock somewhere.

 

Looking at the Novak site there are only 4 parts that they can’t source for the rebuild of the SM420.
https://www.novak-adapt.com/catalog/transmission/transmission-parts/sm420-parts.html

Clutch Gear / Input Shaft
Third Speed Gear
Second Speed Constant Mesh Gear
First and Reverse Gear Assembly

 

I didn't think about that. I suppose I need to start looking into that, as I'm debating starting the whole thing over winter break.

 

When I did mine, I chose a T-18 because parts are available and it's the shortest over all length with adapter. Those were my primary criteria.

My T-18 is the later over-and-back reverse and it seems to shift as nice as the T-14 ever did. I have no complaints with it and love having the low gear for crawling.

 

I wish mine was that style. I hate the way mine shifts.

 

This. I stashed "spare" SM420's for years, for spare parts, have never used a single part, so I have started selling off some of them. I have 3 jeeps that have been Rubiconed for 30 years, and love the SM420. Novak has (almost) everything you need, great support, easy rebuild guide, etc. You will love it, and the crawl ratio also.

 

Someone bing to consider with the SM-420 is there are 3 different versions I’m aware of, although all share the same 7.02-1 first gear. The last one was used in light vehicles in 1967. This can make hard parts difficult to source. The last one I rebuilt it was damn hard to find some parts for, working for a shop that had more contacts than a teenager has pimples, and was well over 20 years ago when parts were more readily available.
I keep hearing “I am not likely to blow this up”. It’s not blowing it up but simply wear that happens over time with any mechanical device. Therein lies the problem. They tend to be noisier than other transmissions due to the shallower angle the gears are cut.
While I’m partial to the T-18 due to size, length when adapted, parts availability, etc., the SM-465 is a great transmission, just large. The NP-435 is a good transmission as well. Both the latter have good support.
But, it sounds like you are set on the 420 so hopefully you don’t have to source the hard to find parts.

 

The t18 will bolt up to the Buick with little mods, it’s shorter in overall length when adaptor is installed, and you can use a factory crossmember to mount it.

 

Are you referring to the 3 "generations" that Novak talks about ('47-'53, '54-'53, & '64-'67)?

 

Along those lines, should I avoid the early ('47-'53) SM420s since they do not have a front seal? Novak talks about them here, but I am a visual learner and can't translate these words into a useful understanding of what they are describing. https://www.novak-adapt.com/catalog/transmission/transmission-parts/sm420-parts.html

If the front seal is worth having, I will probably shoot to find a mid or late case rather than have Novak convert it to a front-seal, as I do not want to spend another $200 plus time waiting on parts (as Novak requires me to ship the mainshaft to them for them to work on it).

 

You want the seal.

 

I'm having a bit of trouble understanding the whole u-joint situation.

From what I'm reading, the stock front driveshaft comes with 1110 u-joints since I have the Dauntless, but a popular upgrade is a 1310 u-joint. The 1310 should fit without grinding if I find a non-webbed SM420 and I can find the proper yoke for the D27.

In a post (I think from Fireball in 2019-ish) I read that this is the proper yoke I would need to get a 1310 on my D27: https://www.northerndrivetrain.com/product/NDT-2-4-2291.html\

What size are the rear u-joints?

It seems I've found yet another subject that I know almost nothing about.

 

the rear joints are 1310s, they're just fine.

as far as transmission selection, i would heartily encourage you to use an sm420. i have on in an old grain truck with umpteen bajillion miles, and it's still working fine. the nicest part is that it will bolt to the 225 with factory buick parts - no monkeying around, just bolt it up. its a beefy transmission with an incredible first, and there are millions of them out there.

 

What is the best way to figure out weather or not a SM420 has the input oil seal? Pulling the front bearing retainer?
I've found a good-looking, non-ribbed SM420 nearby for pretty cheap, but I'm not sure what year it is just yet.
I'm working on figuring out how to decipher the year right now as well based on the casting numbers, but I don't have the casting numbers from the seller yet.

*EDIT*
After watching a handful more videos, I've realized that non-sealed SM420s have the weep hole on the bottom of the input retainer, so as long as that hole is not present, I should be golden.

 

This thread details my 4 speed swap. I used a T18 so it's different from what you're doing, but things like exhaust clearance, floor pan modifications, crossmember mount etc are all relevant.
http://www.earlycj5.com/xf_cj5/index.php?threads/152977/

 

Thanks. I've been looking through a few 4-speed swap threads. I'm a visual learner, so it's always nice to look through build threads and get a visual for stuff like floorboards, exhaust, and clutch linkage.

 

Yes.

 

Alright, I'm lost. I've done absolutely no work or research on clutches before now, and it shows.
How does it all work together? Can I just re-use stock '66 parts on the SM420? I'll probably want to throw a clutch in it, but I can't figure out for the life of me what actual parts I would need, and the specs of said parts.

 

Novak has a page. Suggest you read that and ask specific questions. https://www.novak-adapt.com/knowledge/clutches/clutches-etc.html

In brief, the clutch has a pressure plate aka cover, and a disk with friction material. The cover has to match the engine flywheel, and the disk has to match the splines on the transmission. Both parts must be the same diameter. There is a release bearing aka throwout bearing that must fit on the transmission bearing retainer and match (length) with the cover actuating arms. It ends up being a mix of parts that you choose from those or other sources to be compatible with the engine and the transmission, that will release and engage properly.

All part of the science of swapology. A little thinking, a little research, some experimenting.

Somebody who has done this exact swap may have a list of parts they used.