TX WTB Two-Piece driveshaft SWB TH400

[TravisMartin]

I have a 1978 SWB big block with TH400 & 3.73 12bolt; driveshaft has been lost by previous owner. I'd like to find a correct replacement. I will be retrofitting a 4L80E so will be shortening it.

Question: would the shaft from a long wheelbase truck work; that is, is the length of the rear section from the carrier bearing to the differential the same SWB and LWB, or is the front section the same, or are they both different? In other words, could I use a LWB setup since I'll be shortening the front section for the 4L80E anyway? (trying to open up the possibilities of someone having what I need...)

Thanks!

[BIG V]

Why a 2 piece ?
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[TravisMartin]

Because that is what is original to this truck. The higher (numerically) gear ratio trucks used a two piece since the drive shaft turns faster for a given speed; it is easier to balance the shorter shafts. Much the same as why a two piece pool cue is preferred to a one piece "bar stick."

[BIG V]

I guess that changed in 78 my old 77 bb shortbed bought new by uncle had a one piece, and the 77 bigblock shortbed gmc i just parted had a one piece, however to answer your question a longbed std cab 2 piece could be cut down. I thought the one piece pool que's are refered to as bar sticks because they sit on a rack, 2 piece cue's are easier to transport because they break down. Ive never balanced my que's but maybe i should
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[TravisMartin]

What were the gear ratios on those two trucks? If I'm not mistaken the split was at 3.73; 3.42 and below were one piece. I think. I'd like to know for sure; do you know what rears those two had?

Are you telling me that the rear section of the LWB is the same as SWB? That's what would matter to me; I've got to shorten the front regardless since I'm retrofitting a 4L80E. Trying not to have to modify the rear section, as it would double the cost.

Two piece cues are of course easier to transport, but they are also easier to maintain precisely straight and balanced; if the one piece was as good or better, you'd see tournament players use one piece...ease of transport would take a back seat!

[BIG V]

Seriously the rear section is longer on a long bed the piece under the cab is the same, hence long bed and short bed. So why isn't there 2 piece shafts on suburbans? My uncles was 4:10 the gmc was 3:42 that sorta kills that theory as for the pool cue theory I've never balanced my mcdermits I've never heard of balancing a pool que, i guess that next time i make it to a tournament ill have to ask around about spin balancing them.
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[BIG V]

Maybe i should go to 2 piece in my street car? I just figured it would be easier to put a 1 piece in.
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[cleansquare]

Yes you can use a 2 piece, I just had mine shortened today. The 4l80e is 3.25" longer than the 400 so thats what needs to be taken out of the front driveshaft. Fit perfect.

[TravisMartin]

A very nice looking C-eleven for sure.

I think I'll ask Kieth the assembly line guy if he knows why some were one piece and others two...

I've never seen a one piece cue of better than medium grade, have you? The joint allows the maker to keep it straighter and rounder, both very important traits in a cue. It's been a while since I watched any pros on TV, but I don't recall ever seeing a one piece used in competition, and I don't believe it's because ease of transport is any where near as important as the quality of the cue. But I confess I'm outa my league on pool; never got that good at it.

[TravisMartin]

Thanks, Clean, good info. My truck has a one piece in it now; the previous owner had one fabricated that has a slip joint in it to work with the fixed yoke on the TH400. It works okay, but I'd like to make it as sanitary as possible when I do the conversion. I suppose I could change the output shaft to a slip yoke and use a conventional one-piece, but assumed I'd put a two piece back into it since that is definitely what the truck came with and it would allow me to use the fixed yoke that is already installed on the 4L80E that I'll be using.

[TravisMartin]

By the way, were you able to use the TH400 crossmember with the 4L80E? My impression was that it would work fine by moving it back, but I haven't tried measuring anything yet.

[cleansquare]

yep moved it back easily. Also you need a 4l80e transmission mount for the crosmember, the 400 one wont work. Also need a 4l80e dust pan for the converter, the 400 wont work.

[TravisMartin]

Great; thanks. I'll have the dust pan with the donor; going to swap a 95 454 and 4L80E in and use the ECM and harness from the 95. I'm hoping to be able to mount the ECM over the glove box like in an 87...looks like there's room. My goal is to make it "look" factory.

Is yours a two piece shaft? If so, what is the rear ratio from the SPID?