SM465 to 700r4: Different driveshaft lengths?

[Nick_R_23]

This is going to be quite the convoluted swap so feel free to bail if it gets too difficult to follow along

I currently own a 1987 Chevy V10 longbed that has been converted into a buggy. It’s been severely hacked up, including a bobbed frame and questionable spring relocates. However, the cab is rust free and in great shape, and supposedly the truck only has 47,000 miles on it total. The TBI engine is in good shape, I have a brand new Level 3 700r4 built for it, and a rebuild kit waiting for the working but leaky NP208. It’s a flatbed and the front fenders and core support and have been cut. I’ve thought about finishing the truck, but it’s more work than I think I want to put into it, especially since I don’t have time to go wheeling anymore.

A gentleman up the road from me has a 1984 GMC Sierra, either 3/4 or 1 ton, long bed pickup. It has a title, but the cab is pretty rusty. The engine, transmission, and transfer case are all missing, but the frame, axles, and bed/fenders appear to be all in good or usable shape. The truck is free if I go get it. It used to have an SM465, but I’m not sure what transfer case.

My thought process will be to make a good, usable driving heavy duty truck out of the two. Since my 87 is fuel injected, I would like to keep it that way. My plan would be to swap the 87’s cab, TBI engine, 700r4, NP208, and all EFI components (tanks, lines, harnesses, etc) onto the 84 chassis, and keep the 84 frame, suspension, steering, axles, front clip, and bed.

My main question is this: Will my driveshaft lengths remain unchanged? I have a brand new rear driveshaft in the 87. If I have to have new ones made, it’s not the end of the world, I’m just wondering what my chances are of getting away with just a conversion joint?

[mongocanfly]

about a foot of difference i think

[kipps]

If I got this straight --

1987 v10 complete drivetrain and driveshaft.
1984 k20 chassis and axles.

The 1984 sm465 doesn't factor in at all. The only potential problem I see is where the 1/2-ton driveshaft connects to the 3/4-ton axle.

#1, you "might" need a conversion joint. A 1987 3/4-ton used a 1350 joint, if I remember correctly.
#2, the length might be different, depending on how deep the 10 bolt pinion support is compared to the 14-bolt pinion support. I've never seen both axles side by side to know if there is a difference or not.

I've got a perfectly good 1987 3/4-ton driveshaft sitting here waiting to be scrapped. I suspect the shipping to Alaska would be a deal-breaker, though.

[Nick_R_23]

Yes and no. The V10 has the springs relocated. What this has done to the wheelbase/axle positions, I don’t know, although by eyeball I feel like the rear has been moved forward for some wild reason.

I guess my real question is: How does the SM465/208(?) combo compare in overall length to a 700r4/208 combo? If the 84’s driveshafts are still present, would they work?

[mongocanfly]

Try this
http://forum.73-87chevytrucks.com/sm...;topic=32506.0

[kipps]

If it helps at all, my 1987 v20 with a sm465, np208, and a semi-float 14-bolt rear, had a driveshaft that measured 53" between the u-joints, and was 3.5" in diameter. I don't know the length of the slip yoke right off.

Edit: I'm not completely sure about all the measurements in mongo's link. A 1987 4wd sm465 and a 1990's 4wd nv4500 are almost exactly the same length from the block to the t-case. That doesn't appear to be reflected in that link. Unfortunately, I forgot that measurement. I could get it for you though, if it would help. I've got all the parts for a nv4500 sitting around here, and would just need to measure and tally them up.

Also, by the late 80's, GM was beginning the resizing process to make their transmissions more interchangeable. Some of the automatics were being lengthened or shortened by a few inches to simplify truck assembly. I don't know when these changes were taking place, but the gmt400 trucks were more consistent than the squarebody's on transmission length.

[Nick_R_23]

Hmm. I think my assumption of the rear axle being moved might be right. I measure my driveshaft at 44.5” center to center on the U-joints.

From bellhousing mounting surface to the end of the tail housing on my 700/208 combo is 46” overall. I doubt that a SM465/208 will be any longer.

[mongocanfly]

Hey kipps, it's on the internet so its gotta be true...!!!...that was all I could find with a quick search