The Stovebolt Site Forums The Parking Lot Big Bolts Slip yolk travel when shortening a driveshaft

Hi all - just finishing the details on my axle swap and I have to have the driveshaft shortened.

The rear segment of the drive shaft has a slip yolk on 1 end, bolted to the rear axle on the other. I currently have 1" of travel up on the slip yolk before it bottoms out.

The total length of the splines is 5" so there is 4 inches engaged with no load. I would like to get more "up" travel so I need to shorten the driveshaft but how far do I go? Is there a rule of thumb for slip yolk travel or spline engagement?

Ryan

It would be pretty simple to figure it out by using the old Pythagorean theorem for right triangles: A2 + B2 = C2. No, I can't represent "squared" properly with this keyboard! You'll need to know the vertical distance the rear end travels, the distance between the transmission output shaft and the rear end flange, and the length of the driveshaft. The driveshaft length will be "C", the hypotneuse of the triangle. As the rear end moves up and down, the shortest distance would be when the transmission output shaft and the pinion flange are at exactly the same level. The driveshaft should be at least an inch shorter than that dimension.
Jerry

If you are going to have a drive shaft shop do it, measure the distance between the center of the front and rear U-joint and give them that measurement. That's how I order drive shafts over the phone for our trucks.

I just had 2 driveshafts built for a truck and the guy told me 1" of travel is what he builds into his shafts.

Good luck, George

If you're engaging in some type of stupidity like having a radically raised or lowered ride height, you might need more slip yoke travel than 1 inch. Unless the driveshaft angle is pretty radical, that should be enough.
Jerry

During the 10 years I owned a driveline shop we learned many things along the way. Fortunately none of them were the hard way as we were always extra careful. One of them is that the length of the splines on a slip yoke does not necessarily mean that the transmission will accept this amount of slip. Some may but other do not because while slip yokes are made in a variety of series, lengths, diameters, number of spline, etc. the trannys seem not to always follow what is available. In other words a yoke may have 5" of spline length but the transmission may only accept 4" of it. This is important information because I've seen shafts with the incorrect short yokes simply because it was available. If this were to bottom out it's likely that both the driveshaft and the tranny would be damaged. This is really important on any used vehicle since you never know what your dealing with. If the transmission info is available to a good driveline shop they can figure it out for you and build accordingly. As a general rule of thumb I would recommend 70% of the length the tranny would accept as the proper ammount to go inside the slip yoke. Whenever there was doubt this rule never failed us.

Thanks. The transmission is a fixed yolk, driveshaft is 3 piece and this is the rear section of the 3 piece driveshaft. I will call the local driveline shop.

Ryan