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Old 07-17-2018, 06:50 PM   #1
rsmarr1982
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3 ott 4x4

I wanna swap out my th350 in my 72 k20 for a 3 on the tree, is my 205 the same as one for a 3 speed? Does my crossmember need moved? Also how rare are they, will it be hard to find one?
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1969 chevy c10 lwb stepside 250 6 3 ott
1971 chevy c10 lwb 250 6 with power steering 3 ott
1972 chevy k20 4x4 350/TH350 automatic
1978 chevy Malibu 4dr 305 2bbl (all original)
1979 chevy k10 Scottsdale 350/th350 full-time 4wd(daily driver)
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Old 07-18-2018, 08:25 AM   #2
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Re: 3 ott 4x4

I'm not sure, but I think only the adapter is different. I have taken one out that had a Dana20 transfer case and installed a TH350/NP205 and never touched the crossmember. I have a complete Saginaw 3spd/Dana20 set-up from a Blazer you can have, but a K/20 would have gotten a NP205
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"BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed"

GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project)
GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling)
Tim

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R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~
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Old 07-18-2018, 10:03 AM   #3
Benjamin
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Re: 3 ott 4x4

You might want to do a little research, but I think there possibly are different input shafts on the NP205 t-case, depending on what transmission it is bolted to.

Might I ask why you want the 3 OTT? Depending on your tire size and axle gearing, the 3 OTT 1st gear might not be low enough in some situations.

I have a K10 w 3.07 axles and 35" tires, and it is much more enjoyable to use the granny low gear to take off from a stop.

My buddy in FL has a K20 w 4.11 axles and 37" tires, 4 speed also, but he starts in 2nd in typical street driving, which is about the same as a 3 speed's 1st gear. His 4.11 axles make the difference.

If you ever put it in 4WD, you might like the option of having granny low gear.

Also, how are people gonna know you are driving a stick if your column shifter looks just like an auto? Get the 4 speed and remove all doubt with a glorious four-on-the-floor shifter!

As you may have realized by now, I REALLY like my 4-speed, and would highly recommend it. I had a 3 speed in the 2wd I had in high school, and loved I too, but I think the extra gear down low on the 4 speed comes in handy often.

For comparison, here are gear ratios for 4-speed and 3-speed transmissions, as you can see, the LOWEST 1st gear on a 3 speed is still not as low as the 1st gear on the SM 465 4-speed
(sometimes the SM 465 is shown as having gears LO-1-2-3, which is how it is shown below) There were several variations of the 3-speed transmission, 4 of which are shown.
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Old 07-18-2018, 10:04 AM   #4
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Re: 3 ott 4x4

4 speed vs 3 speed
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Old 07-18-2018, 10:29 AM   #5
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Re: 3 ott 4x4

There are definitely different input shafts. You need to read this article from Advance Adapters.

http://www.advanceadapters.com/tech-...w-process-205/

“In 1971, New Process introduced a model NP203 (chain-driven), and NP205 (gear-driven) transfer case. Both of these transfer cases used various input splines. As a general rule, all of the transfer cases that couple to a TH350 automatic are normally a 27 spline input; when coupled to a manual transmission a 10 spline input; and when coupled to a TH400 a 32 spline input.”

If you read the next few paragraphs you’ll also see that there were different bolt patterns as well, figure 8 from 1971-1984?, and circular bolt pattern from 1985-1991.

And then there are also 2 different stick out lengths for the input shaft.

Something else in this article makes me question if the 4wd 3-speed trucks used the NP205, and makes me wonder if the 3-speeds were using a different t-case, maybe even a divorced unit?

“The 1971-79 NP205 was only found mated to the TH350 and the SM465 transmission”
That being said, I feel like more 4wd came from the factory with a 4-speed manual than did a 3-speed manual.

Best of luck and keep us updated!!
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Old 07-18-2018, 02:16 PM   #6
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Re: 3 ott 4x4

I have one out back, and it's a three speed married to a np205. Crossmember seems to be in the only location to accept the torque bracket. This truck is a 1972 Gmc half ton 4x4. I can take some photos of it. I'm going to be stripping it down to the frame, and powder coating it for a k20 mutt build. So they did make them. As far as the spline count/power sleeve who knows. The tower/adapter on the tranny side appears to be different as well.I bet there has been more than a few guys that swapped them out for 4 spd's that will post up. Would make it pretty hard to steal most can't drive a stick let alone one on the tree. I'll take pics when I get the cab off.
(not a for sale post)
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Old 07-18-2018, 07:55 PM   #7
rsmarr1982
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Re: 3 ott 4x4

I've always liked the nostalgia of a 3 ott, I like it better than four on the floor especially when there's 3 people in the cab. I have a 4.10 year with 265/75/16 tires. When I restore the truck I'm prolly gonna go with an nv4500 but that's years from now. Thanks for the great info.
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1969 chevy c10 lwb stepside 250 6 3 ott
1971 chevy c10 lwb 250 6 with power steering 3 ott
1972 chevy k20 4x4 350/TH350 automatic
1978 chevy Malibu 4dr 305 2bbl (all original)
1979 chevy k10 Scottsdale 350/th350 full-time 4wd(daily driver)
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Old 07-18-2018, 08:23 PM   #8
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Re: 3 ott 4x4

It's your truck to do as you please. I'm sure you thought about it before posting. Advance adapters doesn't have their facts straight. The NP205 was introduced in the '69 Blazer w/TH350, then in the full K-model line in '70. I have owned a '71 K/10 SWB with Saginaw 3spd/NP205. I'm pretty sure there were TH400/NP205s pre-80.
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"BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed"

GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project)
GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling)
Tim

"Don't call me a redneck. I'm a rough cut country gentleman"

R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~

Last edited by special-K; 07-19-2018 at 05:58 AM.
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Old 07-19-2018, 02:04 AM   #9
In The Ten Ring
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Re: 3 ott 4x4

I've always liked the nostalgia of a 3 ott, I like it better than four on the floor especially when there's 3 people in the cab.

Wow, I think you've been reading my posts concerning why I like the 3OTT (combined with bench seat and date nights).

Sometimes I'd like a 4th gear though.

Good luck on your conversion and please post us a build set of pics and info.
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Old 07-19-2018, 08:04 AM   #10
Benjamin
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Re: 3 ott 4x4

Quote:
Originally Posted by special-K View Post
It's your truck to do as you please. I'm sure you thought about it before posting. Advance adapters doesn't have their facts straight. The NP205 was introduced in the '69 Blazer w/TH350, then in the full K-model line in '70. I have owned a '71 K/10 SWB with Saginaw 3spd/NP205. I'm pretty sure there were TH400/NP205s pre-80.
Yeah, I'm not too sure about all the info in that article either, but the input shaft differences are the main thing. With 4.10 axles and those tires you should be fine. My 3 OTT truck in high school had 31 x 10.50s, about the same size tire, and I could even take off in 2nd gear!! if I had to!!

Awesome to see you going from an auto to a manual!

SAVE THE STICKS!!
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