1971 Drivetrain options

[Ryanfj55]

Hi guys,

I'm sure this has been asked before, but I didn't find an answer.

I have a 1971 3/4 4x4 with no drivetrain. I'm wondering what year rigs I can start looking for to find a drop in donor motor/trans/case. Haven't seen too many '71/72's around for donors.

Thanks for the assistance!!

[brad_man_72]

1955-2016 gm will all drop in with some small adapters and redrilling a few holes.

[Ugly 61]

The factory didn't build any big block 4x4's so if you want to go original you'll have to stick to a small block chevy. Big block chevy motors will fit but it'll be a tight fit. Stock transmission options were the 4 speed or th350.
Ugly 61

[Ryanfj55]

Thanks guys,

Any combo drops in as long as it's a 4x4 case?

[barry1982]

You didn't mention if your 71 was originally a standard or auto? Chances are your truck came with a 307 or a 350. If I was doing the job, would try find a mid to late 70's doner truck with everything you need. I believe around 1980 was the last year they used the NP205 transfer case.

[Ryanfj55]

Thanks Barry, not sure (I can check the VIN) what it originally came with. I did get a T350/205 with it when purchased.

[Vintage Windmills]

Are you missing the tcase too? If so, I'd look for a 1970 to 1987 GM 4x4 setup. Just make sure you get a right hand drop tcase setup. On that note, 1989 to 1993 dodge cummins will fit and work well but requires new crossmembers and is a bit more involved project.

[Vintage Windmills]

I was typing as you were. If you have the np205 with auto trans adapters you are in good shape and just need pretty much any SBC. You may want to consider a 700R4 upgrade since it will work with your np205

[Ryanfj55]

Thanks Vintage,

To Brad's point, anything including the 700R4 will bolt in?

[special-K]

The 700r4 is longer than the TH350, so the crossmember for the transfer case will need to be moved back. But first, do you have the driveshafts? If no, then that is a good way to go since the stock front would need to be lengthened and the rear shortened and you'd be having them made anyway. If you do have the driveshafts you can do the 700r4 conversion w/o touching the shafts. You just move everything forward the difference in length and they'll work. Inline 6s in these trucks have mounts further forward and the holes will be in the frame, so just move yours there. 4wd engines sit way back anyway and there is plenty of room in front. Also, the distributor will be easier to work on.

[Ryanfj55]

Yep, got the factory driveshafts.

If I find a donor in my vintage, is there any difference in the frame on a 1/2 ton vs. 3/4 ton when considering swapping over the drive-train?

Thanks guys.

[Ryanfj55]

Vintage,

I do have an opportunity to pick up a 350/SM465/NP205 from a '78 donor. I noticed you have that set up in your '71 K20. Was that a simple swap?

Thank you.

[barry1982]

Hi again Ryan, does your truck have a clutch pedal? If so, the 78 donor will work just fine. Installing a clutch pedal is not a nice job. You will need a 67-72 standard donor for the pedal setup.

[Vintage Windmills]

Originally Posted by Ryanfj55

Vintage,

I do have an opportunity to pick up a 350/SM465/NP205 from a '78 donor. I noticed you have that set up in your '71 K20. Was that a simple swap?

Thank you.

Its what my truck came with from the factory. I think the 78 setup would bolt right in but am not positive. Note that the NP 205 behind the SM465's had a different input shaft than the NP 205 behind the TH350. The coarser splined ones behind the SM465 seem to suffer more spline wear so be on the lookout for that when you have things apart.

In that same truck of mine, I swapped in a 350 that seemed to run well from another K20. I am regretting it now since it has developed a valve issue already. I've got a new crate engine I picked up for 1500 delivered sitting here ready to go in. Should have just bought the crate engine in the first place or rebuilt the 350.

I am pretty sure I'm going to replace the TH350 in my 72K20 with a 700R4. I would really like the lockup converter and to have the engine further forward for servicing as special K mentions. I even have a OD shift indicator for my steering column.

[Ryanfj55]

Thanks Barry/Vintage,

I'll dig out the snow and confirm what I'm working with before landing on a donor.

More to come...

[special-K]

No difference between K/10 and K/20 frames when it comes to mounting drivetrain. Totally interchangeable.