The Stovebolt Site Forums The Shop Area Engine Shop Open Drive Line?

I have a 54 GMC Long-bed with a totally non-original drive train. 261Chevy - SM420 - Drive shaft starts out as a 3/4-ton torque tube up to the carrier bearing and then switches over to a 1-ton open drive shaft back to a ~ 1957 open style 1/2-ton rear-end. How can I convert to an all open drive shaft using the same SM420 4-speed and the 57 rear-end? I know I would need to locate a open style rear bearing retainer for the SM420, but what drive shaft and carrier bearing setup will work for my Frankenstein application?

Jim

If I understand your description, you can keep your carrier bearing and rear driveshaft, then you will have to have a driveshaft made or shortened for the middle. I think having one made shouldn't be too much more expensive than finding an intermediate shaft at a pick and pull and having it shortened with new Ujoints. Certainly save you some time. Should be fairly easy to find the rear bearing retainer for the SM420.

Is something wrong with your TT? All I can think your would gain would be easier servicibility (sp?) should something go wrong in the future and a bunch of jugs of used 90 weight.

I am doing a complete frame-up resto on my truck and I am in the process of rr'ing the drive shaft and rear-end to complete my drive train resto. After seeing what is involved with my torque tube setup, I was thinking that an all open drive shaft might be the better way to go. I would not think my current carrier bearing would work with an open setup, since the center support is connected to the outside of torque tube via a rubber ring and the bearing is in the inside of the torque tube.

Jim

If you are already in there, I agree, time for an open driveline. By big trucks all have open driveline with a regular carrier bearing. I thought the 3/4 ton was the same way. I guess you could just get carrier bearing for a 54 1 ton.

Looking in my factory assy manual it shows a 3600 with open driveline. I assume it is showing a 54 as it has a one piece open driveshaft. Seems like a long distance to span with a single shaft but that is what it shows. Anywho what you describe in your truck is the typical setup for a pre 54 3/4 ton. The 1 ton is different, it's a two peice open shaft.

I have the rear retainer for the sm420 you would need to run the open shaft and I am looking for the u-joint that would go on your setup between the sm-420 and the short closed shaft if you would like to trade. You would still need to find the shaft(s).

Grant, I am interested in obtaining the rear retainer and the U-joint yoke assembly to convert to an open drive shaft setup, but I am doing this for a future upgrade. I plan to continue to use my current setup for a while until I am ready to proceed with the drive line upgrade. I did how ever buy a NOS 3/4-ton u-joint assembly when I came accross one for sale, not knowing if I was going to need it or not. I did install the NOS joint on my tranny, but the old one is in excellent condition if you would like to trade for the SM420 bearing retainer that you have. Do you have the u-joint yoke assembly that goes with it? Also the NOS u-joint assembly did not come with the speedo gear that is press fit onto the front u-joint flange, so I put the one from my old setup on the NOS flange.


Picture of 3/4-ton U-Joint assembly, before speedo gear removal:

http://community.webshots.com/photo/109000222/536892438FHUPRJ

Jim

Might be worth getting some measurements and hitting the wrecking yard for a driveline. I don't know if they all do this,but Pick-n-Pull in Reno has a whole rack of drivelines;you just check measurements until you find one you can use,stop at the parts store to get the u-joints you need to match up the ends to the yokes and you're in business.
Speed