Driveshafts: Swap solutions

When doing an engine swap, we often find ourselves needing a special driveshaft length. I usually retain the original driveshaft from the car getting the swap because it will have the proper u-joint on it to fit the pinion at the rear differential. I get the driveshaft from the transmission I'm using in the swap because it has the proper yoke/u-joint on it that fits the trans I'm using. I whack off the tubes a couple of inches past the joints, retaining the front joint/yoke that matches the trans I'm using and the rear joint from the other shaft that mates with the pinion. With the car positioned at ride height, rotate the rear axle so that you have an up-bubble on the pinion of 2 to 3 degrees for a street machine. Drag cars will want more of a difference between the trans output shaft and the differential pinion because the pinion will be hit harder with engine torque than a street car will and may even be installed with the pinion pointing down a number of degrees. It all depends on the rear suspension system being used. If using leaf springs, there are special angled wedges made for the purpose of changing the rotational position of the housing. The motor/trans will have been installed at about a 3 degree down-bubble, so this will make the crankshaft/transmission shaft parallel with the rear pinion. Notice I said PARALLEL, not necessarily pointing at each other. Bolt the rear joint onto the pinion. Slide the front yoke onto the transmission output shaft until it bottoms and will go no further. Now, pull the yoke out 5/8" to 3/4". Measure between the centerlines of the bearing cups on the front and rear joints. This will be the measurement you will give your shop to make your new driveshaft. Give them the front and rear joints and the measurment and they'll make and balance a shaft for you. If you want it to be bulletproof, specify that you want it built with 0.093" tubing.