Now I want to get the rear drive system a little farther along. There are a few considerations to uh uh consider when setting up the drive on any vehicle. First of all we need to think about the weight of the vehicle. The drive components for a small cart would not be adequate for a Baja racer. Employment of a 1" diameter solid steel axle with a 1/4" key way will be sufficient for our cart. I bought a 1"axle that is 44" long with a step down to 3/4" with a 3/4" male thread that will bolt onto the rear hub. You can see in the next photo how the axle has a step that will bottom against the inside of the wheel hub and allow the threads to stick out far enough to screw on a retaining nut. The wheel hub also has a set screw that can be tightened to secure the key stock that will be inserted in the key way. You could just weld the hub on if you like but you sure would have a hard time changing it out if you need to for some reason.

In the next photo you can see that the threaded end of the shaft is ready to receive the retaining nut. This is another good place to use a nyloc retaining nut because we don't need a lot of bolting torque. It just needs to stay in place.

We need to remember that this cart is set up with rear swing arms that will be flexing up and down. If we were using a straight solid axle it would not be necessary to account for any flexing. But then every bump in the road would try to jar your brains out. So how do we still use a solid drive shaft while compensating for the axial movement? If you said just use some bailing wire I would say close but no cigar. If you said how about using a 1" universal joint then I would say Bingo! A flexible universal joint or U joint is an amazing invention designed to transfer power where there is any offset between the source of power and point of transfer. In our case we will be transferring power from the drive sprocket in the center of the cart to the rear wheels via a flexible universal joint and a section of solid axle. You could also use a Constant Velocity joint. What the heck is that? That is commonly referred to as a CV joint and is used extensively in front wheel drive autos as well as other applications. I have never used a CV joint before but it is something I need to learn to mess with. Maybe next project. I don't know very much about U joints either but it will be well suited for this application. I bought brand new U joints and they are not cheap. Next time I will shop around on E bay and find a deal.

The next picture shows the U joint fitted to the center sprocket jackshaft. The trick now is to determine how long the axle needs to be so it can be cut to the correct length. The axle I bought is a solid axle that is threaded on each end. It is just a matter of cutting the correct length off of each end. My hope was to have enough left in between the ends to use for the center jack shaft that will drive the sprocket. I think my luck is going to run short. About 1 1/2" short to be exact.

I will use a very sophisticated approach to determine the final cut length of the axle. It employs the use of aerial surveying techniques. Simply place the axle with the wheel attached at the proper spot under the U joint and the Azusa flange on the swing arm. Set the wheel at the desired track width. You will recall that wheel base refers to the distance between wheel centers from front to back. Track refers to what? If you said distance between centers from side to side then we need to give you a cigar. The track on the font wheels is somewhere between 55 and 56" so we will shoot for the same on the rear. You need to bear in mind that the drive shaft will need to be free to float in and out of the U joint to compensate for the movement up and down of the swing arm. I figure about 1/4" will be enough.

One final check before completing the precision measurement. Yep looks about right. Actually I did use a tape to measure the distance to the hub. The axle fits into the hub 4 1/8". I hope I don't forget to add that to the overall length of the axle. I think I will go write it down right now.