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Old 10-16-2010, 11:28 PM   #1
Jay146992
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Question sm465 to th400 swap

I have a 1979 k10 reg cab short bed with a sm465 transmission that I want to swap to a th400. I know the 465 is 10 spline and the 400 is 32. I already have a 400 trans and a 32 spline np205 tcase but my question is what will I have to do to make it all fit on the chassis. Will I need to move the cross member? Is there a difference between a 4x4 th400 and a 4x2 th400? (I have no idea what the 400 transmission I have came out of) The np205 32 spline I have has a long tail shaft unlike my other np205 that has a short shaft that was mounted to my sm465. Will I need to change the tail shaft on my tcase? Did chevy make a 350/th400/np205 combo? I would really like to know so I don't have to make custom drive shafts and a cross member. Is the 400 transmission suppose to mount to the cross member or is the tcase? Also what gear ratio would you guys recommend for 0-60 drag? 4.10, 4.11, or 4.56? The engine is a 500 hp 383 stroker and it has 35" tires. What front and rear end should I get? I was thinking a dana 60 combo. It currently has the stock 10 bolt front and 12 bolt rear.
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Old 10-17-2010, 09:59 AM   #2
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Re: sm465 to th400 swap

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Old 10-17-2010, 11:19 AM   #3
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Re: sm465 to th400 swap

Lots of questions in one post.

The 2-wd T-400 has a longer output shaft than the 4x4 version so the transfer case adapter on the NP205 is too short to work with it. You can have the output shaft swapped for the 4x4 version or find a 4x4 T-400. You could make a custom spacer to use the 2-wd trans in the 4x4 but it would cost more than getting a 4x4 trans would so it isn't worth it plus then you would have to get custom length driveshafts built.

The T-400 / NP205 combo is fairly common in 3/4 & 1-tons.

The mount on the transmission goes away when you remove the tail shaft housing so the trans will bolt up to the transfer case adapter. There may be holes in the frame already to just bolt the crossmember right in place or you may have to drill some new holes. From your description it sounds like you have a car or 2-wd truck application T-400. I would put it up for sale and find a 4x4 version to use in your build instead.

With 35" tires, 500 hp and going drag racing in mind I would go with a set of Dana 60's front & rear. What gears you use depends upon what RPM you want to push the engine to. Assuming 6000 rpm shifts, 5000 lbs and 500 flywheel HP running 5.13 gears with 35" tires you would go through the traps a little over 4900 rpm. 4.88 gears would drop it down to ~4700 rpm and 4.56 gears would put it at ~4400 rpm.

I would go with the 4.56 gears as you would still have a decent cruise RPM at 70 mph on the freeway at about 3100 RPM. I run 5.13's & 32" tires and it sucks without overdrive.

My track won't let trucks with selectable 4-wd systems that can go into 2-wd run in 4x4 mode. You might want to check with your local track before you build a 4x4 drag truck.
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Old 10-17-2010, 05:01 PM   #4
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Re: sm465 to th400 swap

why build a 4x4 drag truck? i dont understand why. to much power loss in the big tires and its not as fun as a 2wd truck or a car. i could understand a fast daily driver to have fun with from time to time on the track but why a dragin 4x4?
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Old 10-17-2010, 11:45 PM   #5
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Re: sm465 to th400 swap

Quote:
Originally Posted by 79'84'chevy View Post
why build a 4x4 drag truck? i dont understand why. to much power loss in the big tires and its not as fun as a 2wd truck or a car. i could understand a fast daily driver to have fun with from time to time on the track but why a dragin 4x4?
I'm not restoring the truck just for drag. I might only take it to the track once a year. I'm building it so I can drive it on the weekend, go to shows and take to the track or off road occasionally.

But anyway this is this tcase I have. It has a long tail shaft. Will I need to change it or will that work?
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Old 10-18-2010, 12:51 PM   #6
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Re: sm465 to th400 swap

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Originally Posted by Jay146992 View Post
I'm not restoring the truck just for drag. I might only take it to the track once a year. I'm building it so I can drive it on the weekend, go to shows and take to the track or off road occasionally.

But anyway this is this tcase I have. It has a long tail shaft. Will I need to change it or will that work?
If you are going to run 35's and go off roading you do not want to have a slip yoke transfer case. I would find one from a truck with the two-piece driveshaft so you get the fixed yoke and build a two piece driveshaft to fit your truck.
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69 K20 lwb TBI 350 4L60E NP208 14-bolt Dana-44 w/disc
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79 Malibu TPI 350 4L60 w/ Z28 steering & sway bars
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Old 10-18-2010, 07:06 PM   #7
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Re: sm465 to th400 swap

Quote:
Originally Posted by 68 TT View Post
If you are going to run 35's and go off roading you do not want to have a slip yoke transfer case. I would find one from a truck with the two-piece driveshaft so you get the fixed yoke and build a two piece driveshaft to fit your truck.
Do you have a picture of one like you're talking about?
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Old 10-18-2010, 07:41 PM   #8
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Re: sm465 to th400 swap

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Originally Posted by Jay146992 View Post
Do you have a picture of one like you're talking about?
I thought I had some pics of mine here at work but can't find any.

Here is a link to a pic I found. Hopefully it works.

http://good-times.webshots.com/photo...03881155bNWEif
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69 C10 shortbed stepside 400 small block - built like what a super sport truck could have been
69 K20 lwb TBI 350 4L60E NP208 14-bolt Dana-44 w/disc
68 Camaro SS / RS 500hp 439 inch roller cam big block 4L80E
79 Malibu TPI 350 4L60 w/ Z28 steering & sway bars
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Old 10-18-2010, 08:26 PM   #9
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Re: sm465 to th400 swap

Quote:
Originally Posted by 68 TT View Post
I thought I had some pics of mine here at work but can't find any.

Here is a link to a pic I found. Hopefully it works.

http://good-times.webshots.com/photo...03881155bNWEif
I have the one in that picture also. I couldn't use it on my 400 because it's a 10 spline not 32. My question is could I use parts from the 10 spline tcase and put them in the 32 so it's not a slip yoke? They are both np205's so I don't see why not.

Last edited by Jay146992; 10-18-2010 at 08:31 PM.
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Old 10-19-2010, 11:52 AM   #10
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Re: sm465 to th400 swap

Quote:
Originally Posted by Jay146992 View Post
I have the one in that picture also. I couldn't use it on my 400 because it's a 10 spline not 32. My question is could I use parts from the 10 spline tcase and put them in the 32 so it's not a slip yoke? They are both np205's so I don't see why not.
The input bearing on the 10-spline case is smaller in diameter than the 32-spline version. 80 mm vs. 90 mm.

You can have the case machined to fit the larger bearing and put the 32-spline input shaft & matching bearing into the 10-spline case but since you have two complete NP205's you could just swap out the output yoke parts and not have to machine anything.

Put the 10-spline transfer case back together with the slip yoke parts and sell it off to get some of your money back.
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miSSed opportunity - ground up creation of an AWD 1994 454 SS that never was http://67-72chevytrucks.com/vboard/s...d.php?t=795577
69 C10 shortbed stepside 400 small block - built like what a super sport truck could have been
69 K20 lwb TBI 350 4L60E NP208 14-bolt Dana-44 w/disc
68 Camaro SS / RS 500hp 439 inch roller cam big block 4L80E
79 Malibu TPI 350 4L60 w/ Z28 steering & sway bars
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