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| | | | Joined: May 2004 Posts: 67 'Bolter | | 'Bolter Joined: May 2004 Posts: 67 | Anyone know the length of the drive shaft using a SM420 transmission in a 1959 Chevy 3100. My three speed drive shaft is too short. I assume it will be a one piece drive shaft. Am I correct. I understand that some 59 3100’s did come from the factory with that set up. | | | | | Joined: Mar 2004 Posts: 6,236 'Bolter | | 'Bolter Joined: Mar 2004 Posts: 6,236 | The SM-420 takes a flange yoke bolted to the back of the transmission and a splined slip joint in the shaft. That might be a hard shaft to find. It may be easier to just have your local drive shaft shop make you one. Mike B  | | | | | Joined: Oct 2017 Posts: 54 'Bolter | | 'Bolter Joined: Oct 2017 Posts: 54 | I think the advice above is correct regarding having a shop make up the correct length for your drive shaft swap project. Yes they were a factory option as I have a 1959 3100 with SM420 driving a Spicer 45 rear axle. I cannot measure it now as the truck is back in storage until spring but if you can get your parts in place and get your truck to a drive shaft shop that would not seem a difficult job for them. Yes mine is a one piece propeller shaft with the splined slip joint,
1959 Apache 31
| | | | | Joined: May 2004 Posts: 67 'Bolter | | 'Bolter Joined: May 2004 Posts: 67 | | | | | | Joined: Apr 2012 Posts: 124 Shop Shark | | Shop Shark Joined: Apr 2012 Posts: 124 | I had to have one made for mine with the exact same setup. They told me at the drive shaft shop that I would have to install the transmission and then measure the distance between the transmission and the rear end ( u- joint to u-joint ). It's my only vehicle so that really wasn't an option for me. I subtracted the length of the 4 speed from the length of the 3 speed transmission and added that to the length of the distance between the rear u-joint and the point where the front u-joint would be if it was secured solid to the transmission like on the 4 speed. It took some figuring and I was sweating over it but in the end, they built me a slip shaft that bolted right up. If you can't just measure the distance after you install your transmission and wait on the drive shaft to be built, it isn't that hard to figure it out mathematically. You do have a little bit of wiggle room since it is a slip shaft.
Gene
1959 Apache
| | | | | Joined: May 2004 Posts: 67 'Bolter | | 'Bolter Joined: May 2004 Posts: 67 | | | | | | Joined: Dec 2011 Posts: 112 'Bolter | | 'Bolter Joined: Dec 2011 Posts: 112 | Mule 1951--
I have a 57 3100 factory v8 with SM420 is am in the process of reassembling. Currently the d shaft is loose ( not installed in vehicle) Would be happy to get any dimensions you may need. Let me know here or via pm.
delky dave in wyo
1957, 3100, v8
2016 gmc 4wd
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