The 1947 - Present Chevrolet & GMC Truck Message Board Network - View Single Post - Post pics. Lets see how many 60-66 4x4 are out there.

justcuz · 05-19-2010, 01:27 PM

Your welcome. The SM420 transmission has one of the lowest first gears of a light truck 4 speed, close to 7.0 to 1. So if you double that plus multiply it by your axle ratio ye get your crawl ratio. 7x2x3.73=52.22 to 1. That is rounded up except the axle ratio which should be 3.73 for a half ton unless it was ordered with something else.

Anything over 40 to 1 is considered pretty good.

Keep in mind the new NP 241 aluminum t-cases have a 2.72 to 1 reduction ratio. So a NP 241 behind your SM420 would net you a 71 to 1 crawl ratio!

05-19-2010, 01:27 PM	#305
justcuz Registered User Join Date: May 2008 Location: Alta Loma, Ca. Posts: 930	Re: Post pics. Lets see how many 60-66 4x4 are out there. Your welcome. The SM420 transmission has one of the lowest first gears of a light truck 4 speed, close to 7.0 to 1. So if you double that plus multiply it by your axle ratio ye get your crawl ratio. 7x2x3.73=52.22 to 1. That is rounded up except the axle ratio which should be 3.73 for a half ton unless it was ordered with something else. Anything over 40 to 1 is considered pretty good. Keep in mind the new NP 241 aluminum t-cases have a 2.72 to 1 reduction ratio. So a NP 241 behind your SM420 would net you a 71 to 1 crawl ratio!