SM420 to NP203

cpmarcani · 10-05-07, 05:38 PM

Does anyone know if there is an adapter made to mate a SM420 to a NP203 range box? I have been looking around and don't see anything. I know that it bolts right up to a SM465, but I already have a SM420.

I'm looking to eventually go to a Atlas or Lovell T case.

Thanx

cpmarcani · 10-06-07, 08:56 AM

Other than some obscure Posts on Pirate4x4 it doesen't look like the SM420 is compatible with the NP203. Novak Conversions outright says that on their websight.

If I was going to use a 4sp Atlas I could use the 420 but I am leaning toward the Lovell 357. Which means I will need a doubler, and from what I have found the NP203 is the most durable choice.

Chevy actually used a SM465/NP203 combo in 71-79 Trucks and Blazers, It would be stupid for me not to use the 465 in my application.

The main reason for using a 420 is the 7.05:1 1st gear, realistically there is not that much difference in the 465's 6.55:1 1st. Another argument that could be made it the fact that the 420 uses spur cut gears for 1st and reverse, the 465 uses all helically cut gears, which are inherently stronger.

I guess I answered my own question, thanks for the help anyway.

mrqtipp · 10-06-07, 11:28 AM

Why would you want to? I have ran a sm420 for years and they are very clunky. use a sm465

10-05-07, 05:38 PM	#1
cpmarcani REDBEARD Join Date: Aug 2007 Location: Eagle Rock VA TLCA# 17467 Posts: 116	SM420 to NP203 Does anyone know if there is an adapter made to mate a SM420 to a NP203 range box? I have been looking around and don't see anything. I know that it bolts right up to a SM465, but I already have a SM420. I'm looking to eventually go to a Atlas or Lovell T case. Thanx __________________ 65 FJ40 77 2F Weber DUI/HEI Painless H41 4sp 4.925:1 1st AA Rock Box 3.44:1 Stock TC 2.31:1 (160:1 Crawl Ratio) 78 front axle,disc,ARB,4.11 FJ60 FF rear axle,drum,ARB,4.11 37x12.5 Goodyear MT/R, Allied Rockathons

10-06-07, 08:56 AM	#2
cpmarcani REDBEARD Join Date: Aug 2007 Location: Eagle Rock VA TLCA# 17467 Posts: 116	Other than some obscure Posts on Pirate4x4 it doesen't look like the SM420 is compatible with the NP203. Novak Conversions outright says that on their websight. If I was going to use a 4sp Atlas I could use the 420 but I am leaning toward the Lovell 357. Which means I will need a doubler, and from what I have found the NP203 is the most durable choice. Chevy actually used a SM465/NP203 combo in 71-79 Trucks and Blazers, It would be stupid for me not to use the 465 in my application. The main reason for using a 420 is the 7.05:1 1st gear, realistically there is not that much difference in the 465's 6.55:1 1st. Another argument that could be made it the fact that the 420 uses spur cut gears for 1st and reverse, the 465 uses all helically cut gears, which are inherently stronger. I guess I answered my own question, thanks for the help anyway. __________________ 65 FJ40 77 2F Weber DUI/HEI Painless H41 4sp 4.925:1 1st AA Rock Box 3.44:1 Stock TC 2.31:1 (160:1 Crawl Ratio) 78 front axle,disc,ARB,4.11 FJ60 FF rear axle,drum,ARB,4.11 37x12.5 Goodyear MT/R, Allied Rockathons

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10-06-07, 11:28 AM	#3
mrqtipp IH8MUD Junior Join Date: May 2007 Posts: 102	Why would you want to? I have ran a sm420 for years and they are very clunky. use a sm465