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Damn kids
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SM420: Who has one and how do you like it? What's it in the middle of?
 

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Been running mine for 10 years now, love it. It's compact, has 7:1 first gear, makes lots of cool noises, every farm has one in the bushes or barn. What's not to love?

Oh and mines in a YJ .
 

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Damn kids
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Discussion Starter #3
Been running mine for 10 years now, love it. It's compact, has 7:1 first gear, makes lots of cool noises, every farm has one in the bushes or barn. What's not to love?

Oh and mines in a YJ .
What motor, transfer case and axles? How do you use the YJ?
 

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buddy has one between in his FJ40 between a SBC and some yota t case. The t case just gave out so we were going to swap in a 465/205 combo but holy shit is the 465/205about a foot longer then the 420 and yota case.
 

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The 420 is my favorite transmission for a 4x4. I have a three of them right now, one runner and two spares.

My drivetrain is: AMC 258, SM420, Dana300 (4:1), 1tons (5.38:1). Tires are 38.5" Maxxis Creepy Crawlers.

They make for very short drivetrain which is a plus when you run tight trails where a long wheel base is not optimal. My WB is 100".

I drive my CJ on the road every day. My brother has a rebuilt SM465 in his Jeep, my SM420 seems to shift better.

Also, I run all the local trails which are rocks in the summer and snow in the winter. On snow runs I usually end up being the tow truck because most of the local guys have smaller drivetrains (toy or jeep based).

The 420 in my Jeep now is one of the heavy duty cases with extra ribbing. I got this transmission for free from a junkyard. All I did to put the transmission in my jeep was install the tailshaft adaptor from Novak and replace the syncros (still running the old bearings).

Here's a picture of the ribbing:
 

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It is the bomb you could put a hole in it fill it with water and drive home.

Its for anything but high speed running like sand or mud drags.

Get one inspect it put it in and use it forever....
:smokin:
 

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Ran one for years

First gear sucks for anything other than Granny Low.

With a dana 300 4 to 1, 5:13s you will shift a lot when wheeling, First gear is to low for normal driving, Second gear is 80:1 and 3rd gear sucks for anything other than long flat roads :)

Had one behind AMC 258/204/360 and SBC 350, Dana 300- , Dana 44s/60/14/FJ 60 axles
 

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Wet Trail Wheeler
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95 YJ, 4.3 Chevy , 8.8 Ford rear, stock Dana 30 front, 4.10 gears, spring over.
231 TC with hack n tap slip yoke elim.
Excellent in the rocks, needs CV rear shaft and super short slip yoke elim. with yoke not flange for longest possible rear shaft.

Perfect ratio with 33s, ok with 35s, regear for taller tires.
 

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1969 Jeepster Commando 454, SM420,dana 20 low range 2 to 1,Axles 4.56 gears and , 37 inch tire's.

I consider the results of this combo off road and on road, perfect, very happy with it
 

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I also have one in my jeep.

4.2 I6 and a d300 behind it, 4.10 gears in the axles and stock gears in the t-case. It's a solid transmission but third gear is kind of a bitch sometimes when down shifting for a hill and trying to keep momentum (usually helps to double-clutch).

I have like four spare boxes for parts, not sure if the one I am running has the ribs or not but one of the spares does.

Most of these transmissions have a dripper hole on the front output bearing retainer that will leak gear oil. Look for a small hole (1/4" or so) at the 6 o'clock location.

If you don't mind questionable customer service these guys have a solution that is worth looking into,preferably before installationParts for the SM420 Transmission
 

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I have one of these trans with the ribs. Pm me if any of you mite want it. Has a 350 belhousing and fly wheel and starter.
 

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I have a 4.3/sm420/dana 300 combo to 3.73 gears and it works great for my wheeling. However, I do need to change my axle gears for highway driving pulling steep grades with my trailer. Driving around town, I treat it like a 3 speed.

here's a video of low with my son driving.
 

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had planned on a sm420 but with the cost of adapters and work (which isnt enough really...) required to mate to the jeep straight 6 was enough to make me decide to do the np435. If i was to the sm420 id probably plan and sbc in the plans somewhere.

Far as a trail rig go its tough to beat the overall cost/strength and benefits of the old granny gear 4 speeds. They're damn tough! I absolutley love my np435 and have a total of $500 complete swap including dana 300. having the bump in gearing with the 420 would be nice but im happy where im at
 

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SM420: Who has one and how do you like it? What's it in the middle of?
Good trans - short and lowest of the granny gears but harder to find than the newer truck 4 speeds. Notice the SM420 hoarders that have replied already? :) Depending on the specific details of your vehicle (ie wheelbase, engine, t-case etc), a SM465, NP435, or T18 might be easier/cheaper routes to a similar end - a deep 1st gear, great strength, short overall length compared to a NV4500.
I'm not partial to any one of them in particular, just the best for a specific application. I've got a 420 in an old M43, NP435s in my Dodge and CJ5, and a Ford T18 and T19 and another Dodge NP435 sitting in the garage as spares and future swap into my Scrambler (T18). Advice is to see what's available of all the transmissions that will work in your application, compare prices, and go from there.
 

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I love my 420. It was built from the best (least-worn) parts from 3; 2 sets of internals are still in a box. Mine is wedged between a 3.8 supercharged buick motor and an 18. In a tube chassis buggy. Same transmission since 2004 and it's been all over CA. It came off the trailer and up back door in 2004 for cherry-poppin. The transmission held up much better than my hydro steering. Thank you, WFO (Trevor and Phil) for welding the steering and drinking the Cores to get up Resolution. What a night. :grinpimp:

Bossbuilt said "makes cool noises." No shit. On the trail, I have pulled the top off to check inside to see wtf was going on and it's just 420 stuff going on. Perfectly normal. So, now those are "cool" noises. If I had to explain, you wouldn't understand.

Behind the 18 are a set of 60s and 40s. The 18 is mated to the 420 with an old-school single-output shaft AA adapter. Not a stub shaft. Have broken output yokes and u-joints. 420 is not stressed. It's kinda bored.

I have heard of 420s behind big block chebby and fords. In front of Rockwell and Atlas t-cases. Just about anything. It's a solid unit. Surround it with good friends and you're set up. I think my bell housing is from an early 80's S-10. Flywheel is from a 1999 Camaro and had it balanced for the motor. I fabricated my clutch fork.

Would I use it on the track or for racing? Oh, hell no. It shifts like a old loose whore. Not what you want on a track. But, it is what you want on a crawler or a dump truck.

For technical crawling, it's awesome. Use first. It makes cool sounds.
Use second on the trail or you'll piss your friends off. 1st gear is too deep to keep friends behind you; they tend to revolt and have plenty of time to plan. It's marginally faster than a speed bump.

3rd and 4th are a hoot behind the supercharger in low or high range. I run 5.86 r&p.

So, yeah. I like my 420. Get some.
 

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Damn kids
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Discussion Starter #19
I found a decent 420. '67 with the backup switch, but no ribbed case.

Is the 420 short enough that I can fit a divorced 205 and a workable rear driveshaft?
 
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