Why Are Two-Piece Rear Driveshafts Needed?

[swampdigger]

Hrmm.. well, I pulled the old 460/E4OD out of my '92 SuperCab today. Eyeing things up before I drop my rebuild 6.9/T19 in there. Occured to me now, that I think I'm going to have driveshaft issues. The old combo appears to be a foot longer or so.

!@#!@#!!!!!

So off to the junkyard to find a d-shaft that will work. Is there any silver lining to this--If I have to get a new shaft made, can can I scrap that two piece d-shaft for a single one?

I'm also wondering what junkyard engine/tranny combos will have a compatible d-shaft. Has anyone done any gas to diesel swaps where they kept the driveshafts? Would say a 400M or 460 behind a T-18 or 19 (or that NP thing) and a SuperCab fit the bill?

 

[sassyrel]

Hrmm.. well, I pulled the old 460/E4OD out of my '92 SuperCab today. Eyeing things up before I drop my rebuild 6.9/T19 in there. Occured to me now, that I think I'm going to have driveshaft issues. The old combo appears to be a foot longer or so.

!@#!@#!!!!!

So off to the junkyard to find a d-shaft that will work. Is there any silver lining to this--If I have to get a new shaft made, can can I scrap that two piece d-shaft for a single one?

I'm also wondering what junkyard engine/tranny combos will have a compatible d-shaft. Has anyone done any gas to diesel swaps where they kept the driveshafts? Would say a 400M or 460 behind a T-18 or 19 (or that NP thing) and a SuperCab fit the bill?

dont do it---long driveshafts will cause all sorts of problems---that and driveshaft angles!!!!

 

[NJKen]

Exactly, you can only go so long with a driveshaft before it becomes failure prone. Too much shaft is hard to ballance rotflmao) and harder on the u-joints.
Ken

 

[memphisrain]

Might just try to extend one first. Get a donor driveshaft to use for some tubing, grind off the welds at one of the yokes, pound it out, and weld in the new piece to extend it. You obviously need to be extremely careful here to make the cuts all straight and welding it back together.

I've done a couple and not had any problems out of them. I made a jig using angle iron to make sure the thing was as straight as I could get it, and then measured cap to cap on the u-joints 10 or 15 times to make sure all the lengths were even.

I think it's worth a shot, because if you screw it up, what are you out? Cut it back apart and then take it to a driveline shop and have them lengthen it and balance it.

mR

 

[RWF350]

They are getting hard to find, but if you have a local driveshaft shop they might be able to adjust the length reasonably. Just a thought, but are the yokes on the t-19 and e4od the same? I think you'll have to overcome that as well.

 

[swampdigger]

Well, that makes sense about too long of a shaft. Okay, I guess I'll work WITH this stupid two-piece unit. Thanks guys.

Memphis, that sends chills up my spine! I still have the old d-shaft for the long box reg cab truck my 6.9/t-19 came from. Hmmmmmm... no worries about chopping up that thing. And an excuse to get a decent cut-off saw, and still probably save money. Hmmmmm.....

 

[swampdigger]

They are getting hard to find, but if you have a local driveshaft shop they might be able to adjust the length reasonably. Just a thought, but are the yokes on the t-19 and e4od the same? I think you'll have to overcome that as well.

I guess I should say that both of the trucks in question are 4x4s. I had a BW 1345? that originally came behind the T-19, and a BW 1356 that came with my 460/E4OD.

I did research, and the two will swap, also confirmed by a quick fit-up on the shop floor. I'm going with the 1356 because it reliably engages the front d-shaft (shift pad problem on the 1345), and it will mate up better with the t-case shifter in the '92 truck where it is from.

However, the 1345 has a fixed yoke, and the 1356 has a slip yoke. But I'll put up with the slip yoke to reliably engage the 4x4. And that magnesium case is soooo nice and light to install/remove.

And as such by keeping the 1356, it will hook up to the driveline that doesn't yet fit.

 

[6.9poweredscout]

it's easy to shorten a d-shaft, my friends have done alot of them. the front and rear shafts on the 250 are cut and rewelded. if you have a bandsaw cut along the weld on the yoke, gring the weld off good, cut the shaft with either a bandsaw or chop saw (obvious reasons ) abd burn em back together!

and if a shaft is longer than about 5 feet it gets a "jump rope" thing going. my friend bought a '70's 1700 loadstar 4X4 and the guy removed the transfercase and ran a straight shaft to the rear because someone said it'd go faster..... well my friend was going down a hill and heard a whizzing sound then a pop like a firecracker, he pulled over and everything but the the yokes disappeared! put the t-case back in and made it 4x4 again, no probs!

-Jon

 

[Bobus]

I did a '90 Fsuperduty 2wd 460/5spd to '94 7.3l IDI Turbo/5spd 4x4 Swap.. Was pretty simple. Put a D60 under the front, Put in the '94 Motor/Tranny/T-Case.. Used the '93 Front Drive Shaft, then Cut down the '90 Rear Drive Shaft to fit the rear.

For you guys saying not to go to long single piece drive Shafts.. If there a bad idea.. Why do guys with big lifted trucks go with single piece drive shafts? Other than avoid Shims on the Hanger Bearing?

 

[jperecko]

For you guys saying not to go to long single piece drive Shafts.. If there a bad idea.. Why do guys with big lifted trucks go with single piece drive shafts? Other than avoid Shims on the Hanger Bearing?

'cause guys with any sense do not drive hugely lifted trucks in the first place

...seriously though shafts over ~4 feet long are hard to balance as they, as described earlier, start to "jump rope". They literally flex at higher RPM's and flex back and forth more and more violently until they snap. Nothing garuntees a failure but the longer you go the more likely it is to happen.

I supposed if you really wanted a long shaft (no pun intended) you should use some stupid big stock to build it from that way it will be less likely to flex... but at that point it just makes more sense to have multiple pieces.

When you get a chance, check out the shafts for long box trucks... they are done right with as many as 4-5 shafts, each no longer than about 4 feet.

 

[Goofyexponent]

We had a tandem dump truck like this once. Someone though one long shaft is better than 2 shorter shafts.....wrong.

First time that truck was driven into a jobsite, the DS twisted like a pretzel. It was only idling across the "parking lot" in low gear too. Front tire went into a bit of a depression in the dirt and that's where she stayed.