When putting your car together for a new season, or building a new car from scratch, you need to consider the driveline alignment when mounting the engine and rearend. Because this is one of the basic design features of the car, it can and must be done initially to save a lot of work later on moving things around.
There is now a good deal of information about driveshaft technology and geometry that we have available. Most of this technology has been developed for production cars, but racing applications require a closer look and slightly different approach to this information. The advantages of this knowledge are in the area of reduced power loss and increased component life. The bulk of this information was furnished to CT by Barry Zackrisson. To begin with, we need to know what to call the various components related to our driveshaft.
The component names for the driveline parts are as follows:
Slip Yoke—this is the yoke at the front of the driveshaft that goes into the transmission and can slip to take up the slack of chassis movement.
Weld Yoke—is the yoke at the each end of the driveshaft that attaches to the pinion yoke at the rearend and the Slip yoke at the front. These are welded to the shaft tubing.
Universal Joint Kit or U-Joint (UJ)—is the actual part that forms the rotational connection between the driveshaft and the transmission and rearend.
Tubing—is the metal tubing between the weld yokes.
Pinion Yoke—is the yoke that is attached to the pinion shaft at the rearend.
Driveline Angles—When the UJ operates with any amount of driveline angles, this creates a problem. The bearings speed up and slow down twice per revolution of the driveshaft. This causes an oscillation in the powertrain. The more angles that we have, the higher the peaks of oscillation we see and therefore the greater chance of vibration.
Driveline angles are a cause of vibration and power loss. If your race car must have driveline angles from a design standpoint, the angle of the driveshaft to both the transmission output shaft and the pinion shaft should be equal and also opposite. The angle should also be kept to a minimum when at all possible.
Driveshaft angles are not only measured from a side view, but also from a top view. Some offset Late Model cars can have as much as a 11/2 inch displacement of the rear of the driveshaft from the front. That equals almost 2 degrees of driveshaft angle at both the transmission and the pinion. So, we can align the driveshaft, from a side view, to zero angle and still have 2 degrees of driveshaft angle present.
The latest recommendation might come as somewhat of a shock to most racers, but strictly for racing applications, Zero Driveshaft Angles are encouraged. That's right, based on recent studies and testing, a race car with zero driveshaft angles at the transmission and pinion will not harm the U-joint bearings. The natural vibrations that are produced by the race car will cause the U-joint bearings to rotate enough to stay lubricated and not flat-spot.
In the real world, the driveshaft will never really maintain a zero angle configuration through the diving and rolling of the chassis as we lap the track. Starting at zero means that we will stay very close to zero at all times. For extreme applications, such as when racing at more than 180 mph at Daytona or a similar type of track, the teams will align the drivetrain for zero angles with the car placed at the on-track race attitude.
NOTE: For overall consideration in driveline angle design, number one is to keep the driveline angles as low as possible and keep the angles equal and opposite at each end of the driveshaft.
Controlling Driveline Vibration
The sources of vibration in our racing driveline, in order of importance—most critical at the top, are:
2) Improper driveline angles
3) Looseness in the fit of any of the parts
4) Unbalanced parts
5) Component deflection
6) Reaching critical speed
We will examine some of these causes and see how we can cure many of them just by using better parts that are designed for the racing environment.