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Old 09-28-2017, 02:54 PM   #1
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Auto Trans to SM465 4 Speed Swap in '72 Blazer: Tech Help Needed

Hello All,

I am planning to swap the Turbo 350 Automatic in my '72 K5 Blazer for a SM465 4 speed. As I'm researching the swap online, I came up with a list of questions, that I'm hoping folks can help out with

1. What SM465 should I be looking for? Will the ones from a the '73 to '88 trucks work / link up with speedometer drives / fit properly, or should I seek out one from a 68 - 72 4x4

2. Does it matter if the SM465 is from a 3/4 truck or heavier, or a 1/2 truck?

3. If the SM 465 has a PTO attachment from a farm truck can the PTO setup be eliminated, covered with a plate?

4. Do I want the heavy duty clutch pedal assembly setup with the heavy spring, or the light duty one?

5. Do I want the 10-spline output with a 2-5/8" stickout for my truck?

6. Will my current transfer case work, or do I need to swap the input shaft or swap the whole transfer case?

7. What bellhousing setup should I picked seeking out?

8. Are there any frame mounting crossmembers that I'll need to swap?

9. Which transmission cover should I be seeking out? (High Hump etc)

10. I've seen different shifter handles in different shapes, which one would be right for my year (1972 Blazer)

Thanks in advance! Also, if someone has a stash of this stuff for sale, please feel free to reach out


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Old 09-28-2017, 05:55 PM   #2
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Re: Auto Trans to SM465 4 Speed Swap in '72 Blazer: Tech Help Needed

I've done this exact swap. I am assuming that your Blazer is 4x4. If not then some of my responses may not be accurate.

1) Your speedo drive will be on the NP205, not the SM465, so it doesn't really matter if you have a drive on the tranny or not. A tranny from a 2x4 truck will have a fixed yoke on the output shaft. You would need to change the output shaft in the tranny to get the correct 10-spline output needed to duplicate the stock setup.

2) I am not aware of any differences between the 1/2 and 3/4 ton truck versions. However, I believe there is a wide-ratio version and a close-ratio version. The wide-ratio version has the super low granny first gear, and the close-ratio has "normal" first gear ratio. Basically, you start out in 2nd gear with the wide-ratio version and only use the granny gear for starting when pulling really heavy loads, plowing, or crawling. With the close-ratio version, you start out in 1st gear. The wide-ratio version has bigger gaps in gear ratios need to get to the 1:1 4th gear from the granny 1st gear.

3) Yes.

4) I am assuming that you are referring to the spring weight in the pressure plate. Typically, heavy springs will give you more clamping pressure to the clutch disc preventing slippage. But this usually comes with a stiffer clutch pedal. If you will be towing, plowing, mudding, or generally hammering on the go pedal, a heavy duty pressure plate may be what you want.

5) Yes. That is, if you are going for a stock SM465 to NP205 setup found in these trucks. That 10-spline output is coupled to the NP205 10-spline input via a female 10-spline coupler that resides within the adapter between the two cases. However, there are other, newer SM465 to NP205 combos that have different mating requirements that I am not schooled in. Others may provide that info.

6) You will need to swap in a 10-spline input shaft to work with the coupler discussed above, if you are going for a stock 67-72 setup.

7) There are steel and aluminum SBC bell housings available for our trucks. I went with a steel version. Both should work fine. If its a SBC bell housing, it should have provisions to bolt on the SM465.

8) No. If you go with the stock SM456 to NP205 setup, the transfer case will mount in exactly the same position as it is with the TH350. The TH350 is the exact same length as the SM465 with the adapter.

9) High hump 4x4 with openings for the SM465 and NP205 sticks.

10) The 67-72 4x4 SM465 shift lever has only a single bend. The two wheel drive versions have two bends, as do the later model 4x4 sticks.

One thing you need to be careful about is selecting the proper z-bar, frame side z-bar mount, and engine side z-bar ball stud mount. There are different versions for 2x4, 4x4, I6, and V8 applications. They are not interchangeable, trust me!
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Old 09-28-2017, 08:25 PM   #3
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Re: Auto Trans to SM465 4 Speed Swap in '72 Blazer: Tech Help Needed

Thanks cleszkie! This is super helpful, but I also was realizing more questions as I was reading your responses, so here goes the follow up list:
1. Gotcha, but is there a year range I should be shooting for? Or does it not matter at all? I’m thinking of just making sure that linkages and shift levers line up with the holes in a high hump transmission tunnel cover on a 1972, and a general preference for it to be relatively “correct” since the truck is pretty nice.
2. The close-ratio version sounds more useful for what I use the truck for, what applications were these used in? Or how do I tell which one is which (close ratio vs. wide ratio?
3. Thanks!
4. Actually, I was asking about the pedal assembly itself, there’s two different size return springs, and mounting brackets for the springs on the pedal assembly. I assumed it probably doesn’t matter, but wanted to ask if one was preferable
5. Cool and Thanks!

Also, one more question: Does the clutch pedal assembly need to come from a 4x4 truck to work with the 4x4 V8 Z Bar?
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Old 10-04-2017, 01:31 PM   #4
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Re: Auto Trans to SM465 4 Speed Swap in '72 Blazer: Tech Help Needed

1) That I couldn't tell you. I just hunted down a 4x4 version, but had to do the output shaft "update" to het the 10-spline output.

2) I have never personally seen a close ratio version, or know of the correct casting numbers to look for. I have only seen and dealt with the wide ratio versions. For that matter, perhaps there is no close ratio version. I was only assuming that there might be one out there. A quick google search would answer this question.

4) My pedal assemble has two springs - a heavy one and a light one. They both work together, along with the long return spring under the truck between the frame rail and the clutch fork. I am not aware of any other variations.

5) I imagine that GM only produced one clutch pedal assembly and had multiple z-bar assemblies to make it work with many applications. So your 2x4 pedal assembly should be good for a 4x4.
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Old 10-05-2017, 09:41 PM   #5
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Re: Auto Trans to SM465 4 Speed Swap in '72 Blazer: Tech Help Needed

There are no "wide ratio" and "close ratio" SM465 trans. They are all wide ratio. The BW T18 has a wide and a close but not the SM.

Your best bet for a donor is a blazer or suburban as they aren't typically driven as hard as trucks are. Especially true of 3/4 and one tons. And I would certainly try and get a trans/t-case combo still bolted together to make sure you have all the parts you need.

SM465 were used through '91 in Blazers, Subs, and the square body trucks. But some of the later ones use a slip yoke on the 205 and not the bolt on u-joint with slip driveshaft which is what you want IMO.
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Old 10-06-2017, 10:22 PM   #6
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Re: Auto Trans to SM465 4 Speed Swap in '72 Blazer: Tech Help Needed

I have everything you need from the steering shaft to the transfer case.
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Old 10-07-2017, 04:38 AM   #7
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Re: Auto Trans to SM465 4 Speed Swap in '72 Blazer: Tech Help Needed

I have a 10 spline t/case and a th350, I bought an adapter power sleeve that coupled them together rather than trying to change out the input shaft of the t/case. I got it through Advanced Adapters. If you look to go this route, double check that you can use their power sleeve with the original transfer case/transmission adapter.
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