1982 standard transmission into 1970 auto 4X4

[stingray_]

I have a 1970 GMC 1/2 ton that is automatic, and has a 350 motor and TH350 transmission. It is a 4X4.

I also have a 1982 GMC 3/4 ton truck that is 2 wheel drive. The '82 is a three speed with granny (Low) gear.

Is there a way to adapt the standard transmission from the '82 into the '70?

1.) If this is possible, who makes adapters or what is the process? I know I will need pedals, the bell housing for the small block and driveshaft lengths may need to be changed. etc.

2.) Would there be any gear ratio problems?

3.) Are there better standard transmissions for this? What is the ideal standard transmission for this sort of application?

4.) Is this a good idea? opinions?

Thank you,
Ray

[stingray_]

anyone?

[Yukon Jack]

The 4 speed should be the SM465 and all you need to swap it in is the correct adapter. I would imagine Advance Adapters could help you or you can get one from a junk yard or possibly the parts board. In addition to the items you listed that you will need, you will also need the pilot bushing.

Someone else were verify as I don't know automatic info very well, but I think you can use your existing transfer case crossmember, may have to move it back or forward though.

Again I don't know automatics but I assume you need a different flywheel and of course you will need a clutch, throwout bearing, clutch fork and related clutch linkage.

As to whether it is a good idea, depends on what you are trying to accomplish. The SM465 is ultra strong, but the same final 1:1 gear ratio as the TH350 and TH400 for that matter.

You won't use the 1st gear in every day driving, but that low gearing is great when needed.

I'm pretty sure the driveshaft issue is answered in another post, but that might be difficult to find - someone will let you know on that issue too I'm sure.

[sierra4x4]

The 4 speed tailshaft will be the wrong length. It would be easier to find a 4x4 trans with the correct adapter on it. The SM465 came in 3 main variations:
1-SM465 mated to the "203" t-case(fulltime) '73-'74 I think
2-SM465 mated to the "205" t-case(part time, gear drive) '73ish-'91ish
3-SM465 mated to the "208" t-case(part time, chain drive, aluminum)'81-'87
The Sm 465 mated to the "205" is a bulletproof combination. I have a 465-205 combo in my 74 3/4 ton with a 427 and love it, you cant hurt it. If you need more info just let me know. Can you tell me some more details about the 70 like engine(stock or hopped up,diff ratios,tire size etc. also primary use for the truck.

[Yukon Jack]

Whoops, missed that the new SM465 is a two wheel drive unit.

Welcome to the board sierra4x4!

[stingray_]

My truck mostly seems like an unmolested 1970 GMC truck. It has a 350, with a newer TH350 transmission. I am trying to figure out what transfer case it has. I remember it was a heavy cast iron one, and I'm sure that is still the original. I would like to convert the truck to manual tranny, and I like the idea of having a granny gear. I would also like to change the axles to 3/4 ton since my GMC is only a 1/2 ton.

My thinking is to find a 3/4 ton Chevy truck with 4X4 manual and take all the components to upgrade my '70 GMC. I m just looking for the correct year that would give me the best combo. Of course I would also like to lift it during the process of changing the axles.

What should my transfer case be stock i cant remember if its NP203 or NP205. I know that is still OG.

Thank you...for your response

[1969 GMC]

Originally Posted by stingray_

My truck mostly seems like an unmolested 1970 GMC truck. It has a 350, with a newer TH350 transmission. I am trying to figure out what transfer case it has. I remember it was a heavy cast iron one, and I'm sure that is still the original. I would like to convert the truck to manual tranny, and I like the idea of having a granny gear. I would also like to change the axles to 3/4 ton since my GMC is only a 1/2 ton.

My thinking is to find a 3/4 ton Chevy truck with 4X4 manual and take all the components to upgrade my '70 GMC. I m just looking for the correct year that would give me the best combo. Of course I would also like to lift it during the process of changing the axles.

What should my transfer case be stock i cant remember if its NP203 or NP205. I know that is still OG.

Thank you...for your response

you have got the right idea...get any '72 or newer chevy/gmc K20/2500 with the 4 speed and swap it all out.

and yes, your current t-case is the NP205.

[stingray_]

So from 1972- ? what year should I look for?

What is the best tranny available that would be a four speed plus granny? I'm looking for one that would would adapt to my NP205?

Also will any 3/4 axles work or should what is the best 3/4 axles to look for? Alot comes to mind with the axles.

Any advise is appreciated. Also thank you for the advise you guys already gave me too.