Driveshaft question
 

I am converting my 68 short bed from small block, TH700R4 and 2 piece driveshaft to a 396, TH700 R4. Since I have to move the transmission back 1.5" to accommodate the engine, can I use a one piece driveshaft that will be 58" long?

Re: Driveshaft question
 

I always rely on my some what local drive shaft shop for their direction. Length, diameter and max engine rpm all factor into the design of the drive shaft. I would upgrade to 1350 u-joints.

Re: Driveshaft question
 

I went from a long bed to a short bed and I'm running a driveshaft a little longer than 58", based on several other builds I studied. I'm not on the road yet so take that for what it's worth.;)

Re: Driveshaft question
 

I have a swb 396/700r4 with a single piece ds. I want to say it was 58.5” but that’s just from memory.

Re: Driveshaft question
 

Part of what determines the limits of drive line length is the intended usage along with gear ratio, tire diameter, transmission top gear ratio, engine horsepower. These factors determine the maximum RPM of the driveline as well as how much torque it will be required to absorb.

There is a maximum RPM that a drive line can turn at before it starts it reaches critical speed. The length, diameter, and material used in the driveline determine its critical speed. The critical speed is basically the RPM at which the drive line starts to whip or bend so it resembles a jump rope which can be felt as a vibration in the vehicle. Exceeding the critical speed will lead to driveline failure due to fatiguing of the driveline material. The longer time and/or the greater amount of RPM you exceed the critical speed causes the failure to happen sooner.

Spicer has calculator to help determine what the critical speed of your driveline would be.

https://spicerparts.com/calculators/...rpm-calculator

Then you need to calculate what the maximum RPM your driveline would turn at to see if you're in danger of exceeding the critical speed.

https://www.dennysdriveshaft.com/pot...alculator.html