The Stovebolt Site Forums The Shop Area Engine Shop one for the gear ratio guys

I have a 51 Chevy 6400 W/2speed rear and am wondering if I swap the SM420 for a Muncie M20 will it hold up (stong enough) and will the gearing work, plan on insalling a S/B in as an engine, was planning on going with a gear venders unit to solve the low top speed problem. Do plan on using the truck for hauling dirt

I guess you have accessed gear vendors site where they list the available gear ratios? I don't think they under drive the first gear, do they? The 420 has a 7.08 first gear and I think the M20 is about 2.94(?). That would be the problem I see; not a low-enough low for heavy pulling or hauling.

The close ratio gears would not be practical in a bigbolt like that. You may want to use the latter model 4 speed sm465 1968 up. It,s a tougher trans.

thank you both I will look into the sm465 and see what i can find availble the m20 is free to me thats why i was checking

The M20 is free! Grab it and trade it for a pile of SM465s!

Concur with OldSub, snap up the M20 first. You don't want to give up the granny for hauling.

I am going to a SM465 with a gear splitter (got it cheaper than a gear vendors unit) to replace the crash box in my 39.

The SM465 doesn't buy you anything over the SM420 for all practical purposes. A backup light switch and a sychro first ain't worth the work.

I really like gear vendors stuff but, it is super expensive. The US Gear overdrive unit I am using will work and will work great for the price I paid used.

Since you have a vacuum rear end, you could add another lever to your floorboard in the form of an Advance Adapters Ranger Unit for less than $1500 giving you an overdrive (sort of) at a reasonable price. I like these units behind a 235 or a mild small block. I would leave it in overdrive for regular driving around town and drop it to direct for any necessary hauling. It moves your shifter back 7 inches and you will have to shorten your driveshaft. I mostly like these for price.

Or a Richmond Truck 6 speed with a 4:1 first (not short enough IMO) and an overdrive for about $3500.

Or a Dodge NV4500 using a Dodge to SM420 adapter plate would be great.

well I had not been to the gear vendors site but had read alot about them and thought I would take a look Very good stuff but Iam sure you guys know alot cheaper ways to do it $3000 to do it thier way was not what I had in mind. as Ive said before Iam still early in the planning stage thats why Iam asking the off the wall ???? just kicking around some ideas.