drivetrain swap - The 1947 - Present Chevrolet & GMC Truck Message Board Network

blazomatic · 06-21-2003, 09:42 PM

I have a 71 k-5 with 307 and 3-speed on the the column. I just bought it a few months ago. I think it's great but my problem is when I tow a trailer it doesn't have a low enough 1st gear. I am pulling a med. trailer with atvs. I would like to swap to a 4-speed but I don't know how hard it would be. The owners manual list 2 diffrent 4-speeds. The 465 and the np-435. It also list the ratios of them. I think the 435 has the better ratios for what I need. I know it would help towing. The truck runs good with the combo I have now and I hate to tear into it. It just doesn't pull a load well. The transfercase is a Dana 20. 4-speed and auto trucks came with 205's. So if I swap will I have to go to a 205 as well? Would an engine making more torque and the three speed work? I don't know what the rear gears are. On the highway it does about 2200 rpm at 60 mph. I'm thinking 3:08 but somethings I have read say blazers came with 3:73's. Any suggestions would be appreciated.

Mike C · 06-21-2003, 10:16 PM

Get a complete 465/205 combo. It is excellent for trailering. The 435 in a 4 wheel drive is REALLY uncommon, but the 465/205 combo can be found well into the 80's.

2200 sounds just like 3.08. You could switch to 3.73 or so, but you would have to do both ends, and it would negatively affect your cruise rpm but help with towing significantly. I vote for the 4 speed and keeping the 3.08, assuming you are running stock size tires. If you go to 31s, you really need 3.42, 3.73 for 33s, and 4.10 for 35s.

My Jimmy worked pretty well with the stock 350 motor, 3.07 and the 465. It was a dog with the big cam, 33's and the 3.07 however... Great again with a little cam and 4.10 turning the 35s.

Longhorn Man · 06-21-2003, 11:56 PM

Might be easier to swap in an engine with more low end grunt,a nd leave the tranny/transfer alone.
More torque will walk right over the poor gearing.

06-21-2003, 09:42 PM	#1
blazomatic Registered User Join Date: Jun 2003 Location: s.e. tenn Posts: 28	drivetrain swap I have a 71 k-5 with 307 and 3-speed on the the column. I just bought it a few months ago. I think it's great but my problem is when I tow a trailer it doesn't have a low enough 1st gear. I am pulling a med. trailer with atvs. I would like to swap to a 4-speed but I don't know how hard it would be. The owners manual list 2 diffrent 4-speeds. The 465 and the np-435. It also list the ratios of them. I think the 435 has the better ratios for what I need. I know it would help towing. The truck runs good with the combo I have now and I hate to tear into it. It just doesn't pull a load well. The transfercase is a Dana 20. 4-speed and auto trucks came with 205's. So if I swap will I have to go to a 205 as well? Would an engine making more torque and the three speed work? I don't know what the rear gears are. On the highway it does about 2200 rpm at 60 mph. I'm thinking 3:08 but somethings I have read say blazers came with 3:73's. Any suggestions would be appreciated.

06-21-2003, 10:16 PM	#2
Mike C Registered User Join Date: Dec 1999 Location: Austin, TX, USA Posts: 7,721	Get a complete 465/205 combo. It is excellent for trailering. The 435 in a 4 wheel drive is REALLY uncommon, but the 465/205 combo can be found well into the 80's. 2200 sounds just like 3.08. You could switch to 3.73 or so, but you would have to do both ends, and it would negatively affect your cruise rpm but help with towing significantly. I vote for the 4 speed and keeping the 3.08, assuming you are running stock size tires. If you go to 31s, you really need 3.42, 3.73 for 33s, and 4.10 for 35s. My Jimmy worked pretty well with the stock 350 motor, 3.07 and the 465. It was a dog with the big cam, 33's and the 3.07 however... Great again with a little cam and 4.10 turning the 35s. __________________ 44 Willys MB 52 M38A1 64 Corvette Coupe 68 Camaro 'vert LT1 & TH700 69 Z/28 355 12.6's @110 69 Chevy Short Step 4 1/2"/7" drop 72 Jimmy 4WD 4spd 4" & 35's 02 GMC 2500HD 4x4 Duramax

06-21-2003, 11:56 PM	#3
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Might be easier to swap in an engine with more low end grunt,a nd leave the tranny/transfer alone. More torque will walk right over the poor gearing.



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