SM420 (1 Viewer)

[Jakes40]

Can anyone tell me if this is a good price for this.
--GM truck Muncie 4 speed with granny gear, SM420, $125
It is a local person "MD".
And I am being told the Muncie 4 speed is not the SM420 not sure.
I've never been a Chevy man.

This may be the direction I go for gearing.

Thanks
Chris

 

[John Smith]

Ask them what vehicle they pulled the tranny from and ask for a picture if it. I would jump on it for that price if it is complete and in working condition. My guess is that it is probably a SM465 which does not have as low of a granny first but is almost identical otherwise.

 

[kulangot]

The 420 is easier to swap into a Cruiser with a stock F/2F but the 465 is a better trans overall. Yes, the 420 has a lower first gear but many of them don't have a front oil seal and most all of them are pretty well worn.

The gear spacing on either is not ideal of a stock cruiser six with big tires but works well with a V8. IIRC mine had a big lag between 2nd and 3rd gear. They are also VERY loud and whine a lot.

You'll also find that with such a difference between granny low and 2nd that it's hard to keep momentum if your trying to climb out of something with tire speed and or wheel spin. I ran a similar trans with 35's and found that I had some trouble going up hills where you had to drop down a gear. I had to really slow down as the RPM drop was huge but the motor lugged in 4th. Again, a strong V8 would not have trouble though.

If you don't plan to drive on the street, none of this will be a factor but unless you trailer, you have to drive it to the trails...

I'd say get a Orion or an Orion HD. But, a lot of people have swapped in 420's and like them.

Keep the stock driveshaft length and be able to run junkyard spares. No adapter to mess with. Send your core to Mark Algazy or to Mudrack and it comes back ready to rock.

 

[Jakes40]

the only driving I will be doing is acationaly around town. I'm building it to wheel. I plan on trailering it.

 

[kulangot]

For that kind of use, you'll probably like it.

Here is some reading for you:

The GM Muncie SM420 Transmission - Novak Conversions

-Stumbaugh

 

[Jakes40]

thanks Stumbaugh thats a good site

Chris

 

[Cruiserdrew]

I've had an SM420 in my FJ40 for 7 years or so. There is no better source of cheap off-road gearing for a Land Cruiser. You still need a bunch of parts to run it, but the one pictured is an SM420-you can tell by that big reverse gear bulge in the side.

Pull the top cover off and look at the gears. If they are not rusty or worn too bad, the price is right. I'm not certain, but that one does not appear to have the cast webbing of the later SM420s so it's probably an older one. If it were me, I'd make sure it's the one with a real seal for input shaft before I bought it.

Pinhead has a great write up for how to determine the year from the numbers cast on the other side of the transmission.

They do whine a bit, but in a 40 it really isn't that bad.

Read this: sm420

 

[Jakes40]

Thats what I'm looking at fairly cheep gearing.
I've read all the write ups in tech section on this bourd and others.
the seller is sending me pics of the casting no. can't check email right now.

thanks for the info