SM420 and NP205 - The 1947 - Present Chevrolet & GMC Truck Message Board Network

stelth2002 · 11-11-2002, 09:54 PM

Did they make this combo? The sm420 is one of the strongest trannies that i have known and many people agree, what about you? I have a 2wd version that I want to convert to a 4wd married to the t/c. Is this hard? I know finding one is nearly impossible. Has anyone did this swap and do you think that it would put up with 650-750 ft-lbs torque? What would be the strongest drivetrain to put up with that kinda power. Thanks

GMC71k20 · 11-11-2002, 10:08 PM

what do you have that will put out 650-750 ft/lbs of torque?

stelth2002 · 11-11-2002, 10:56 PM

A tuned up cummins 6bt. Im thinking about using a GM tranny/tc. It would be smaller and cheaper to use by several 1K. Thanks

Rod · 11-12-2002, 12:11 AM

Seen the sm240 / np205 married combo in a couple 69's. That would be the year of truck I would check for that combo....

stelth2002 · 11-12-2002, 12:12 AM

The Sm420 was only produced from 1948-1967 i believe. They were put in the bigger 2.5 ton trucks all the way to 1/2 tons. Was it a stock combo you think or modified? I need all the info I can get.

Blazer1970 · 11-12-2002, 08:43 AM

If there ever was a 420/205 married combo, it was very rare. I have never seen or heard of it. SM465/NP205 on the other hand, is just as strong and there are tons of them out there. That is what I would use.

stelth2002 · 11-12-2002, 11:30 PM

Anybody else have any advice for me? The reason I want to go with the sm420 is that it is just as strong, but it is 2 inches shorter and 50 pounds lighter. You may not think its much, but if I can it would help my driveline angles and the engine is going to weigh 400 pounds more than the stock one, so I would like to sheer some pounds were I can. In the pre67 how is the 4 wheel drive setup?? Anyone know?? Thanks

11-11-2002, 09:54 PM	#1
stelth2002 Young Gun wth Fast Inline Join Date: Jan 2002 Location: Idaho Posts: 1,475	SM420 and NP205 Did they make this combo? The sm420 is one of the strongest trannies that i have known and many people agree, what about you? I have a 2wd version that I want to convert to a 4wd married to the t/c. Is this hard? I know finding one is nearly impossible. Has anyone did this swap and do you think that it would put up with 650-750 ft-lbs torque? What would be the strongest drivetrain to put up with that kinda power. Thanks __________________ 1967 Chevrolet LWB with built 292! 415 ft. lbs of torque, 4 speed :O with 27% overdrive too, 3.73 Posi. Frame and body done... getting painted!!!

11-11-2002, 10:56 PM	#3
stelth2002 Young Gun wth Fast Inline Join Date: Jan 2002 Location: Idaho Posts: 1,475	A tuned up cummins 6bt. Im thinking about using a GM tranny/tc. It would be smaller and cheaper to use by several 1K. Thanks __________________ 1967 Chevrolet LWB with built 292! 415 ft. lbs of torque, 4 speed :O with 27% overdrive too, 3.73 Posi. Frame and body done... getting painted!!!

11-12-2002, 12:11 AM	#4
Rod Join Date: Dec 1999 Location: Eastern - Manitoba Canada, Winnipeg Posts: 4,369	Seen the sm240 / np205 married combo in a couple 69's. That would be the year of truck I would check for that combo.... __________________ Senior active founding member. 70 3/4 ton GMC Suburban 4x4 250/4 spd. 71 1/2 ton Suburban Chevy 4x4, 350/350 72 Chev 1 ton tow truck 402BB w/Holmes 440 wrecker on propane 2005 FLSTSCI Harley Springer 85 FXSB Harley Lowrider 72 Triumph 650 Bonneville 5spd "Poor people don't have hobbies" Quote from wife.

11-12-2002, 12:12 AM	#5
stelth2002 Young Gun wth Fast Inline Join Date: Jan 2002 Location: Idaho Posts: 1,475	The Sm420 was only produced from 1948-1967 i believe. They were put in the bigger 2.5 ton trucks all the way to 1/2 tons. Was it a stock combo you think or modified? I need all the info I can get. __________________ 1967 Chevrolet LWB with built 292! 415 ft. lbs of torque, 4 speed :O with 27% overdrive too, 3.73 Posi. Frame and body done... getting painted!!!

11-12-2002, 08:43 AM	#6
Blazer1970 Registered User Join Date: Dec 1999 Location: Old Mission, MI, USA Posts: 2,507	If there ever was a 420/205 married combo, it was very rare. I have never seen or heard of it. SM465/NP205 on the other hand, is just as strong and there are tons of them out there. That is what I would use. __________________ Tim

11-11-2002, 10:08 PM	#2
GMC71k20 Registered User Join Date: Aug 2002 Location: mass Posts: 1,277	what do you have that will put out 650-750 ft/lbs of torque?

11-12-2002, 11:30 PM	#7
stelth2002 Young Gun wth Fast Inline Join Date: Jan 2002 Location: Idaho Posts: 1,475	Anybody else have any advice for me? The reason I want to go with the sm420 is that it is just as strong, but it is 2 inches shorter and 50 pounds lighter. You may not think its much, but if I can it would help my driveline angles and the engine is going to weigh 400 pounds more than the stock one, so I would like to sheer some pounds were I can. In the pre67 how is the 4 wheel drive setup?? Anyone know?? Thanks __________________ 1967 Chevrolet LWB with built 292! 415 ft. lbs of torque, 4 speed :O with 27% overdrive too, 3.73 Posi. Frame and body done... getting painted!!!



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