If you have a good driveshaft, you will never notice it, but if you've got a bad one, it will be a nightmare. Vibration from an incorrectly balanced or assembled shaft will result in excessive noise and short U-joint life. Although anyone with a hacksaw and a welder can assemble a shaft, getting one right requires experience and professional equipment.
Many kit car builders need specialized driveshafts to mate up various engines and transmission combinations with independent or live-axle rearends. My project Devin was in need of a custom shaft to join the Chevy 283/T-10 running gear with a DeDion rearend.
To begin the job, first determine the size of the U-joints needed. There are three basic sizes: 1310 (approx. 3 1/4 inches wide with 1 1/16-inch or 1 1/8-inch diameter caps), 1330 (3 5/8 inches wide with 1 1/16-inch or 1 1/8-inch caps) and 1350 (3 5/8-inch side with 1 3/16-inch caps). The 1350 is also thicker than the other two and is recommended for racing cars with over 400 hp. For high performance you will want heavy-duty U-joints, and for racing you need ones without grease fittings (which weaken the joint). KC
Pick a yoke that fits the...
Pick a yoke that fits the U-joints you have chosen. You can mix U-joint sizes at each end of the shaft, but the strength will be limited to that of the weaker joint. Push the yoke all the way in, then pull it out 1 inch. Cars with independent rearends (where there will be no plunge on the splines) only require about 1/2 inch of pull-out.
Measure the length of the...
Measure the length of the projected shaft between the centerlines of the two U-joints. If you have a live axle, support the rear end on jackstands or measure with the car on the ground.
At the shop, the tubing for...
At the shop, the tubing for the new shaft is measured to match the dimensions provided. A used driveshaft can be cut down, but only if it is in perfect condition (damaged shafts should not be repaired). For racing special thick-wall tubing should be used. You can also choose between 2-, 2.5-, and 3-inch-diameter shaft tubing. The larger diameter tubing is stronger, but first make sure you have clearance for it in your chassis and driveshaft tunnel. I went for 2.5-inch tubing for the Devin.
The tubing is cut to length...
The tubing is cut to length on a power saw.
The ends are dressed with...
The ends are dressed with a file to eliminate burrs.
A level is used to make sure...
A level is used to make sure the yokes are exactly parallel.
The new yoke is tapped into...
The new yoke is tapped into place.
The transmission yoke is assembled...
The transmission yoke is assembled onto its U-joint.
The driveshaft is chucked...
The driveshaft is chucked into a lathe and leveled.
A dial indicator is set up...
A dial indicator is set up to measure runout on the shaft. A hammer is used to tap the yoke until the shaft runs true.
Once everything is aligned,...
Once everything is aligned, the yoke is welded in place.
A U-joint is assembled on...
A U-joint is assembled on the rear of the shaft.
This strobe is used to check...
This strobe is used to check the shaft for balance. High-speed balance equipment allows the operator to precisely place a metal weight that will balance the shaft and prevent vibration.
The weight is spot-welded...
The weight is spot-welded onto the shaft. The placement of this is critical.
Tape is wrapped around the...
Tape is wrapped around the U-joint to keep the caps from falling off until the shaft is installed. This simple trick can save you a lot of time looking for dropped bearings. When you assemble the joints onto the pinion yoke, torque the nuts to 17 ft-lb on 1310 joints, and 20 ft-lb on 1350 series joints. Overtightening leads to premature wear.
Now that we have the driveshaft...
Now that we have the driveshaft installed, we need a driveshaft hoop to prevent injury or damage should a U-joint fail at speed. The pre-bent 1-inch diameter (5-inch id) hoop was purchased from Jegs (PN 550-40751), while the bottom was made from 1-inch square tubing, radiused on the ends to match the curvature of the framerails.
With the shaft in place, assemble...
With the shaft in place, assemble the parts to provide at least 1 inch of clearance around the driveshaft. The hoop should prevent the shaft from digging into the ground should the front joint fail (which has an unfortunate effect on the car's rearend), and from flailing into the driver should the rear one give up (which has an unfortunate effect on YOUR rear end). If you have a live rear axle, check clearance at all possible driveshaft positions to make sure it doesn't hit at full droop or rise. Also make sure it doesn't interfere with your parking brake or driveshaft tunnel. The Jeg's hoop was 10 inches tall and had to be cut down with a hacksaw. First weld the hoop to the base, then the base to the chassis. Total cost for the shaft and hoop was around $200. Now, that's a shaft...can you dig it?