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Setting up the pinion angle is one of the most misunderstood parts of a chassis puzzle. Here’s the deal that a lot of folks get wrong: The entire notion of setting pinion angle has little or nothing to do with traction (although improved traction can come with it due to zero bind). To maintain the universal joints and the driveshaft in a more or less straight line, the pinion angle has to be correct when the car is under load. In most cases, pinion angle is measured between the pinion gear flange and the driveshaft along with the transmission slip yoke and the driveshaft. Correct angle isn’t only important to a drag racer; it’s also very important in other forms of motorsports, along with any number of street vehicle applications.
Let’s start at the beginning. Ponder the rear suspension in the car when it’s under power and everything “wraps up.” Chassis forces drive the pinion upward - at an angle that turns out to be way too high. According to Mark Williams, the optimum angle for any driveshaft to run at is 1/2 degree. This is the spot where many vibration and frictional problems prove non-existent. In order to minimize power loss and vibration in an offset configuration, the pinion centerline and the transmission centerline must be parallel. Typically, the largest angle for racing applications should be 2 degrees and the centerlines should be parallel within a few 10ths of a degree. If the chassis has some type of a parallel traction bars system, the angles should remain parallel throughout the supension travel.
Jerry Bickel concurs. Accordingly, he states: “There should be no pinion angle (0-degrees) on acceleration, or vibrations, power loss and universal joint breakage can result.”
Remember that with suspension movement, the operating angle will increase, but it should not exceed a few degrees. If the parallelism of the centerlines changes, the u-joints travel at uneven operating velocities. This causes vibration , the same problem created by poorly phased end yokes. Experts like Williams and Bickel are quick to note that this vibration is hard to distinguish from an unbalanced driveshaft.
Keeping the above in mind, the idea is to make sure the pinion is in the correct “location” under power. Under acceleration, the pinion nose moves upward. That means it is typically set nose down while the car is static. Mark Williams states that some of the most common information (or perhaps misinformation) on setup was derived from the very early years of Mopar racing. The very early Chrysler cars had a very thick spring and, as it turns out, it was subject to wind up. In an effort to make allowances for this wind up, Chrysler recommended the pinion should be dropped down a few degrees. This was an effort to have the center lines running close to parallel when under power. If your car has OEM style rubber suspension bushings, a pinion angle of -3 to -4 degrees is likely necessary. Basically, this nose down attitude was originally conceived so as to compensate for the compression due to the rubber bushings.
In order to set the pinion angle on a four-link car with adjustment capability (for example, a drag race four link), you lengthen or shorten one or both of the upper bars to move down or up. In a triangulated four link application (factory GM or Ford), the upper bars are also used to set the pinion angle (here, by adjusting both uppers the same direction and same amount – we’re assuming the car has aftermarket bars with adjustment capability).
What about leaf spring cars? Here you can use wedge shaped aluminum shims to move the pinion up or down (see the accompanying photos). These aluminum wedges effectively rotate the pinion upward or downward depending on which way the wedge is facing. Lakewood offers them in two-degree and four-degree examples for passenger cars, as does Calvert Racing. Bottom line here is, there are dozens of different choices out there when it comes to wedge plates (shims).
That’s a wrap for this issue. Next week, we’ll complete our look at pinon angle. We’ll also take a brief look at driveshaft critical speed. This goes hand in hand with pinion angle. Watch for it.
The angle of the pinion can move significantly. Well-sorted race cars are always set up to compensate. Check out this Super Stock Modified car. It’s nailing the tire to the starting line. Getting the pinion angle right is part of it.
Image courtesy Mark Williams Enterprises
This illustration shows an exaggerated example of pinion angle. Basically, it all boils down to universal joint operating angles.
With a modified stock style four link (triangulated setup shown in the author’s old Buick Regal), the upper bar adjustment is for two purposes only – to set the pinion angle and to center the rear end (from side-to-side) in the car.
Here’s another angle on the previous photo.
Image courtesy Jerry Bickel Race Cars
Jerry Bickel advises that while the car is under power, you must be certain the pinion angle is zero.
Image courtesy Jerry Bickel Race Cars
In order to get to a pinion angle of zero under load with something like a race four-link, Bickel states, you’ll probably need a pinion angle facing downward 1-2 degrees.
Image courtesy Jerry Bickel Race Cars
This illustration lays out an easy way to check and adjust pinion angle on a race style four link.
