Hi,
I hope some one has run across this situation. What I have a is a 54 3/4 ton GMC When I got this truck no engine or tranny came with it. I have a 56 235 6 cylinder with a 3 speed overdrive from a 55 chevy. The problem is when I put the driveline in it all fits but it appears there are two areas that give room for flex within the drive line. What I mean in a car with a three speed the yoke has a inch or two that the drive line can go in and out if needed as the car goes down the road. With the 3/4 ton set up that I have it has that room in the tranny but also has that same ability where the two sections of the drive shaft come together. This is causing some vibration at times. I believe the original set up would only have this at the drive line not at the tranny. The drive shaft, yoke section at the tranny goes into the tranny and then I will also get that same travel at the section where the two drive shafts meet causing it to vibrate as I go down the road.

I have to apologize I don't always know the names of some parts. I hope this makes some sence. The yoke that is attached to the tail section of the drive line is 7 inches long, I have another yoke that would fit out of a 53 chevy but it also is 7 inches long. It seems to me if I was able to find a yoke that was at least 8 to 9 inches long that would take care of the problem Even if it travels it still would keep the drive line from vibrating. Does anyone know of a 3/4 ton truck that might have that yoke form a 60,70 or 80,s pick up. Also if anyone knows of another solution I would be very greatful. once again this is not the original tranny for this truck.

Thanks Steve

GMC engines were a couple inches longer than the Chevy engines. If you located the 235 based on the front mount, then the engine and tranny are too far forward, assuming everything else is of the same length...

Thanks for the reply gearhead,

Sorry I should have been clear on the frame it is actually a 53 chevy 3/4 ton. Because of the same reason. I did not have a gmc engine and wanted to run a inline 6 cylinder and the 235 out of a 56 pickup is the one that came with the 53 frame. It did not fit the gmc frame so I went with the 53, plus that frame had been sanded and painted black already which saved me some work at that time. I am sure the problem is in the drive line having two spots that will slide when there should be only one.

I am planning a trip to the local u pull it and see if I can find one with the same number of splines that will fit and take care of this problem, or another solution.

Thanks Steve

My 76 GMC body sits on a 1981 Chassis. I get confused too.

Would a new or modified driveshaft help the problem?
In Pine Bluff, the place for driveshafts is the local machine shop. They prefer you to take the vehicle there on a trailer and the Machinists do the measuring.

If you measure it wrong, they charge twice, If they measure it wrong it's on them.

I believe the '54 and earlier 3/4 ton trucks used a torque tube section behind the transmission?

I don't have experience with this setup, but I would think that if you were using a '55 vintage open drive transmission, then I would look at what was used on a 55-59 3/4 ton truck. I think the wheelbase is the same. Just take some measurements and then go to the salvage yard.

This might help you.

http://50chevy.freeservers.com/Suspension_Widths.html#Suspension

Thanks Gearhead,

I did not think about the 55-59 set up on a 3/4 ton because those did not have the torque tube drive lines and the set up might be just what I need. Might put an add in craigs list.

Thanks Drew, for the web site this will come in handy for my next project.

Thanks Pinebluffdude, That will be my last option, I still have the drive line out of the 53 the back section length is longer then the one in the 54 that I can have a shop cut to the correct length. the front section is set up for the original tranny and will not work with my tranny.

Again thanks for the feedback
Steve

The 3/4 ton pickups had a stationary yoke on the back of the transmission that bolted to the output shaft rather than a sliding yoke.

The transmission that you have with a sliding yoke will require that you get a 1 piece driveline made up. I just went through this on a similar truck and it ran about $300 for everything new made from scratch at 6-States in Portland Oregon

Thanks,

Ken I thought I might have to go that way I just don't know if having a one piece driveline is recommended for a long bed. I will look into it.

Steve

Steve,

I know of at least two long bed trucks that have had this done with one of them doing a cross country run of over 3000 miles with no problems. Both trucks have 302 GMC motors that are regularly driven like a rental.

Dang.

Ken,

Sorry it has taken me a long time to respond, I have been unable to sign in under my account at home, you know computer problems. Thanks for the response, that is good to know it will probably be what I will end up having to do, at least before I take it on a long trip in the future.

Thanks again Steve