How long is TOO long for drive shafts???

6BangBronk

6BangBronk

Well-Known Member
Joined
Jul 15, 2005
Location
Durham
Putting together a crew cab. Found an interesting transmission combo for sale that would put my front drive shaft at near 82 inches (u-joint to u-joint) and rear at near 54 inches. Was hoping it would equal out but after decyphering, it seems to be odd shaft dimensions to go with. VERY interesting transmission setup (NV4500 with gear vendors overdrive with fixed yoke). But then I'd want to put a divorced transfer case behind it to make it 4x4.
This would be a tow vehicle only. Doubt front would be used much unless just to get out of a rut. But I'd hate to feel what 82 inches felt like at full spin when a u-joint failed.:eek: Kaaa WHAP! Does that seem too long for a front shaft??? Future issues???

Thanks.
 
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I would be more concerned with clearance issues than it being too long. An almost 7' driveshaft is getting up there in length for most single piece driveshafts, but not unheard of, and with those longer single piece driveshafts the overall diameter of the shaft tends to go up (to increase the critical speed, which is the rpm that the material starts to bow from the rotational forces) , with the front driveshaft having up and down and slight side to side movement, I would say you would have to map out clearance to exhaust, transmission, oil pan, etc very carefully. Not only that, ground clearance would begin to be an issue as well. I think you would be much better off with a two piece and mounting a carrier bearing farther up, around the location that the transfercase would normally be located. This would keep the diameter of the tubing smaller, eliminate any clearance issues up to that point, and you would have less of a pole vault/slinging stick under the truck.


This is for heavy duty trucks, but there is some good reading here:
http://www2.dana.com/pdf/J3311-1-DSSP.pdf


I did a quick calculation on Dana's website, the critical speed for a 80" long 5.2" diameter driveshaft was only 2600rpm. I know you said you only intended to use it to get out of ruts at slow speed, but lets say you left the hubs engaged=driveshaft spinning at highway speeds, and lets say your truck does 65mph at 2300rpm...you think you are borderline, but still safe? Think again, with the .73 OD in the NV4500, your shaft is actually spinning over 3100rpm. BOOM. You would need to start stepping up to 6", maybe even larger to have a safe driveshaft at highway speeds, it starts getting more difficult to stick a 6" shaft that moves around with the suspension than 2.5" two piece shaft.
 
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That's what I thought. Good reading! Never heard of an intermittant bearing on a front???

But regardless, there's no sense in having anything on a vehicle of known danger. A truck needs to be fully capable with all equipment complying with the skinny pedal...

I think I'll pass but this would be cool for a 2wd application if anyone else was interested? 78% overdrive that's fully capable of towing while saving 5'th gear of the transmission. Gear Vendors is good shit!!! I bet I'll never stumble upon a combo like this for sale again. And this is confirmed a '95 model being the only GM NV4500 that is adaptable (with Advanced adapter) to a Ford bellhousing.


http://raleigh.craigslist.org/pts/3624359364.html
 
As a rule of thumb we will not make a Shaft over 70"'s. It tends to have a "jump rope effect" after that length. In other words the center of the tube slings out of spec with the speed it's going and makes it nearly impossible to balance. As said, the longer the shaft the bigger the tube diameter has to be.
 
I've been kinda wondering how long of a shaft could be made too. The one in my K30 is 3" tube, 60" long. The Silverado is 3.5" tube, 63" long. Both are 1410 on both ends. My S10, however, has a factory 2 piece (reg cab, long bed with a 4spd) and when I do my LS motor swap and toss the turbo on it, I was really hoping I could get away with a 1 piece so I don't have to screw with a carrier bearing. I'd guess a turbo 4.8 would be rough on one of those :D

Guess I should go pull a tape and see what kinda length I'll end up with.
 
I'd have to measure to be sure but, I'd be willing to bet the rear drive shaft in my Power Wagon is at least 7' and dang near 5" diameter (and it is stock!), if I remember, I'll measure it tomorrow. Were I building a custom shaft though, I personally would go the carrier bearing route for something that long.
 
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