72 K10 Manual to Automatic Conversion

[MikeandCheryl]

Thinking, at this point, of making the truck more driveable for the better half. Thinking of an automatic transmission and transfer case to replace the SM465. Anyone have any experience with this? Pros and cons? Looking at a more modern engine/trans combo, wondering if both front and rear ends will need changing to suit the gearing/alignment difference. thoughts? It seems like more work, however if all my drive train needs rebuilding, costing gets closer. Resale? Drivability? Reliability? tx.

[my67c20]

I changed out the SM465 for a TH350. Found a donor truck and was able to get the column, pedals, flexplate and crossmember. It was easy to unbolt the old and bolt in the new that I questioned why I waited so long. Hardest part was routing the transmission cooler lines, but even that was easy. Had to get driveshaft yoke changed, but again it was easy. Had to wire in a neutral safety switch and backup lights, but there is enough info on this forum and google that even that was easy. All in, probably spend less about $500. Took me longer, but that was because I painted and rebuilt what I could.

[mrein3]

Originally Posted by MikeandCheryl

Thinking, at this point, of making the truck more driveable for the better half. Thinking of an automatic transmission and transfer case to replace the SM465. Anyone have any experience with this? Pros and cons? Looking at a more modern engine/trans combo, wondering if both front and rear ends will need changing to suit the gearing/alignment difference. thoughts? It seems like more work, however if all my drive train needs rebuilding, costing gets closer. Resale? Drivability? Reliability? tx.

I went from a 3-speed on the tree manual to a th350 automatic on my K10. I was fishing a lot back then and was able to get by but that 3-speed really liked to jam at the boat ramp - the worst possible spot for it.

GM made the overall length of the transmission and transfer cases the same for all options available in 1971 and 1972. The difference was made up in a longer or shorter transmission to transfer case adapter. And if you stick with 1971 and 1972 stuff they all bolt on to the same cross member.

If you want to go with an overdrive automatic, it wasn't offered in 1971 or 1972 so to get one you have to go to aftermarket pieces. For example a 700r4 with an Advanced Adapters output shaft made just for that swap.

I did my swap around 20 years ago and have never looked back.

[MikeandCheryl]

GM made the overall length of the transmission and transfer cases the same for all options available in 1971 and 1972. The difference was made up in a longer or shorter transmission to transfer case adapter. And if you stick with 1971 and 1972 stuff they all bolt on to the same cross member.

Thanks for this information - well done. Maybe all i need to find is the transmission and adapter - i have the NP205 Transfer Case from existing. And i suppose a new steering column is in order, although I'm not opposed to having a shifter on the transmission itself - not sure this is even possible.

A new drive train from a more modern vehicle might be a possibility, but i'm unsure how much is interchangeable - like, do I need new front and rear diffs due to the off center measurements for the different t-cases. A headache, perhaps. I'm not wanting this truck to take forever to get running too.

all good comments, and i thank you.

[mrein3]

Originally Posted by MikeandCheryl

GM made the overall length of the transmission and transfer cases the same for all options available in 1971 and 1972. The difference was made up in a longer or shorter transmission to transfer case adapter. And if you stick with 1971 and 1972 stuff they all bolt on to the same cross member.

Thanks for this information - well done. Maybe all i need to find is the transmission and adapter - i have the NP205 Transfer Case from existing. And i suppose a new steering column is in order, although I'm not opposed to having a shifter on the transmission itself - not sure this is even possible.

A new drive train from a more modern vehicle might be a possibility, but i'm unsure how much is interchangeable - like, do I need new front and rear diffs due to the off center measurements for the different t-cases. A headache, perhaps. I'm not wanting this truck to take forever to get running too.

all good comments, and i thank you.

Sadly no. Your transfer case has a ten spline input shaft. The auto has a 28 spline input. You need a t-case, adapter, and th350 from a donor. The good news is everything else bolts up. Your old drive shafts. Same differentials.

You will need an auto steering column.

The t-case/adapter/tranny is truly a drop the manual stuff and bolt in the auto stuff job.

That stuff is heavy! When I did it I was pals with a guy that had a shop. We did it off hours, on a hoist. We bolted the case/adapter/tranny together on the ground. Put that assembly on a tranny jack with a cherry picker. Then with lots of hands holding things steady used the tranny jack to put it in place in the truck.

[MikeandCheryl]

Nice and thanks.
so I'm on the hunt, I guess. We'll see how it goes.
I have the advantage in that all this heavy stuff will be installed from the top - one piece at a time - with my cherry picker. then, I will put the cab on. Hope it's as easy as it sounds...

[57taskforce]

Originally Posted by mrein3

Sadly no. Your transfer case has a ten spline input shaft. The auto has a 28 spline input. You need a t-case, adapter, and th350 from a donor. The good news is everything else bolts up. Your old drive shafts. Same differentials.

You will need an auto steering column.

The t-case/adapter/tranny is truly a drop the manual stuff and bolt in the auto stuff job.

That stuff is heavy! When I did it I was pals with a guy that had a shop. We did it off hours, on a hoist. We bolted the case/adapter/tranny together on the ground. Put that assembly on a tranny jack with a cherry picker. Then with lots of hands holding things steady used the tranny jack to put it in place in the truck.

No offense but thats not true. The 205 from a 465 and a th350 can be interchanged quite easily with the correct adaptor and the correct input shaft. No need to replace the case itself when you can get the input shaft and adaptor brand new from the aftermarket. You can easily get by with just a 4x4 th350 if you have trouble finding a whole 350/205 complete setup. Also note the input shaft swap isn’t necessary either because advance adaptors and others make a conversion sleeve that joins the fine and coarse splines, so that is an option too. My personal preference is to swap the gears because the 10 spline setup isn’t as strong as the 27. The th400 GM 205 is the only GM spec 205 bare case that is physically different than the other GM 205s. It has a larger input bearing but can still be made to work to the the other GM applications. Here’s a few links.


https://www.advanceadapters.com/th35...-10spl-coupler
https://www.advanceadapters.com/4847
https://www.advanceadapters.com/5188 this should be the input gear if memory serves me right. It’s been a while since I messed with a th350 spec 205.

[cj847]

Originally Posted by MikeandCheryl

Thinking, at this point, of making the truck more driveable for the better half. Thinking of an automatic transmission and transfer case to replace the SM465. Anyone have any experience with this? Pros and cons? Looking at a more modern engine/trans combo, wondering if both front and rear ends will need changing to suit the gearing/alignment difference. thoughts? It seems like more work, however if all my drive train needs rebuilding, costing gets closer. Resale? Drivability? Reliability? tx.

By "all my drivetrain needs rebuilding" are you including engine, transmission, transfer case, and rear ends? If so, then your options are endless. Also, "more drivable for the better half" to me translates to an LS swap including it's attached transmission and transfer case. It will require a new front axle assy that is driver drop OR adapt an old passenger drop transfer case to the 4l60 or 4l80 (the transfer case from an 87-91 K5 I think is a bolt up option - passenger drop).

[MikeandCheryl]

Well, to be fair, driveline rebuilding really means checking the entire package over for damages and ensuring things are not too far gone in the wear and tear direction. So far, I'd say the clutch is burnt and done, the input coupling for the Transfer Case has seriously mashed teeth (the 10 spline), ditto for the SM465 output shaft. I have the front and rear diffs out, but not yet opened for inspection. Brakes, rotors, all probably in the same condition as everything else I've pulled off the truck - beat. So new is in order.
But an LS swap? That's a bigger job than this one that I'm already over my head with. But I've done some reading on this forum and it's doable - maybe even a better way to go. At least the gear in the truck won't be 50 years old.
In the end, rebuilding an old truck is really a test to your credit card limits.
(News flash: I did find a TH350 and a NP Transfer case locally, condition unknown, however the case is a 203, and not a 205, so another study session in what fits what is needed. Not sure their driveline measurements are exact enough.)
Thanks for the input - this forum is certainly excellent for information.