The Stovebolt Site Forums The Shop Area Driveline Slip joint driveline question

So I am currently trying to figure out what driveshaft I should put into my 1951 1/2 ton. It now has a 1964 SM420 open drive shaft and a 1957 HO32 chevy rear axle. I have the axle that fits the rear end so I can use that end to build a shaft. What do you recommend for the front ( I assume I’ll need a slip joint front since the yoke on the rear of the transmission is fixed). The length center-of-joint to center-of -joint is 63” and I want a single shaft. Is there anything out there that is close or do I need a front yoke and build a shaft?

I was advised by the local driveshaft expert to use a two piece shaft; 64" was too long in his opinion. Obviously, with a two piece shaft a steady bearing is required. Slip joint is used on the rear of the front shaft at the steady bearing. I got a core from a 68-71 GMC 4x4 and gave it to the drive shaft guy with the measurements needed.

Before I talked to the expert, I wasted a lot of time prowling wrecking years with a tape measure looking for a one piece shaft that would work. There was a Dodge one that might work, but the diameter of the tube was huge. It seems the longer the shaft, the bigger the diameter. Thinking back to my old structural engineering days, that would make sense.

I doubt that 63" is too long for a single shaft. My Ford Supercab Longbed has a 2 piece shaft, but both halves are about 4 ft long. I can understand why they put a 2-piece under that, but 63" isn't that long.
You will need a slip joint in the shaft, typically installed at the front. Should be an easy thing for a driveline shop to fab for you, either from scratch or modifying an older one. Just find something that's long enough with the right rear yoke and let them do the rest, installing a slip yoke and spline on the front end.

OK, then. My advice is simple. Talk to the guy who will be cutting/welding/balancing your driveshaft(s) first.

I agree. The real experts are the ones that do it on a daily basis. I'm just an amateur when it comes to driveshafts, but I have had a few rebuilt/shortened.

Snowman51
Assuming you are working on a 3100 series, AD truck (short bed) and, assuming that in my 1957 3100 w/SM420 has a comparable length driveshaft, I offer the following:
my (org) driveshaft is in the neighborhood of 60"+ long. Single shaft with slip just rear of the transmission. Served me well for ~200,000 mi in 60's, 70's and 80's. I will be reinstalling it when current and long going resto is complete. Trans, shaft and rear end are as from factory.
delky dave in wyo

Snowman51
Assuming you are working on a 3100 series, AD truck (short bed) and, assuming that in my 1957 3100 w/SM420 has a comparable length driveshaft, I offer the following:
my (org) driveshaft is in the neighborhood of 60"+ long. Single shaft with slip just rear of the transmission. Served me well for ~200,000 mi in 60's, 70's and 80's. I will be reinstalling it when current and long going resto is complete. Trans, shaft and rear end are as from factory.
delky dave in wyo

Yes it is a 3100 AD short bed, it now has a 1964 SM420, but has a 1957 HO 32 rear axle. Both ends have fixed u-joints so I will need a slip joint either in the front or the back. Will. A ‘57 3100 have a slip and will the shaft be enough length?

As I see your issue, only actual measurement will answer that question.
Mine (as stated above) has slip yoke that attaches to rear of SM420. Mine is currently in my garage & not in truck. Would be happy to measure OA length between u joints & get them to you. Please advise. Good luck
delky dave in WY

I believe you have a dropout style differential. Go to a driveshaft shop and tell them what you have and you want a driveshaft with a slip yoke for a sm420. They will advise and tell you what measurement they need and build it for you. One piece will work fine.

Option: there will be 55-59 trucks with dropout diff and SM420 to salvage a slip yoke driveshaft from. 57 is 114" WB and 51 is 116" WB. Shortening or lengthening an existing D/S may be cheaper.

PM sent to Snowman51
delky dave in wyo