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Talk about pinion angle and you’ll get a dozen different opinions, and likely some arguments too. The truth is, the geometry involved isn’t laced with magic. With something like a drag race four link, you can set things like IC location independent of the pinion angle, and that tends to start the confusion. Keep in mind, too, the angle of the pinion might have a lot more to do with the health and efficiency of your drivetrain than it has to do with traction - traction is actually secondary here.
Given that, let’s start at the very beginning. Ponder the rear suspension - when it’s under power, the rear end and rear suspension “wrap up.” Here, the pinion is driven upward (which, obviously, is out of whack). Mark Williams notes that the optimal angle for any driveshaft to run at is 1/2 degree, where many vibration and frictional problems are nonexistent. So to minimize power loss and vibration in an offset configuration, the pinion centerline and the transmission centerline need to be parallel. In general, the largest angle for high performance applications should 2 degrees and the centerlines should be parallel within a few tenths of a degree. If the chassis has some type of a parallel traction bar system, the angles should remain parallel throughout the suspension travel.
When it comes to pinion angle, Jerry Bickel concurs: “There should be no pinion angle (Zero-Degrees) on acceleration, or vibrations, power loss and universal joint breakage can result.”
As a result of this, you have to set the pinion angle to take into account changes in geometry as the car hooks and accelerates down the track (or road).
Fair enough, but keep in mind that with suspension movement, the operating angle will increase; however, it should not exceed a few degrees. If the parallelism of the centerlines changes, the universal joints function at uneven operating velocities. This in turn causes vibration (which can also be created by poorly phased end yokes, but that's another story). The vibration a car experiences from an out-of-whack pinion angle is difficult to distinguish from that of an unbalanced driveshaft.
Typically, the pinion is set nose down (static) in order to ensure that the pinion is in the correct location with the car under power. How much it is set down depends upon the specific car. Mark Williams explains that some of the most common information (or even misinformation) on pinion setup originated from the very early years of Chrysler racing. Those Mopars had a very thick Super Stock spring and even though it was thick, it was subject to wind up. In an effort to make allowances for this wind up, the pinion was dropped down a few degrees. It was done this way in order to keep the universal joint centerlines running close to parallel when under power. If the car has OEM style rubber suspension bushings, a pinion angle of -3 to -4 degrees is likely more appropriate. Williams also advises that this nose down attitude was originally used to compensate for rubber bushing compression and compliance.
When it comes time to set the pinion angle on a four-link car with adjustment capability (a typical race car with a four link), you can lengthen or shorten one or both of the upper bars to move the pinion up or down. On a triangulated factory four link (typical late model coil spring GM or Ford applications), the upper bars are also used to set the pinion angle (by adjusting both uppers the same direction and same amount).
If the car has stock leaf springs, you can use wedge plates (wedge shaped aluminum shims) to move the pinion up or down. The wedge plates effectively rotate the pinion upward or downward depending on which way the wedge is facing. The wedge plates are designed to sandwich between the rear end housing perches and the leaf springs.
Pinion angle should be checked and adjusted any time there are changes in the chassis that have an effect upon the ride height or the length and location of the suspension link bars. Before establishing the pinion angle, Jerry Bickel advises you should have the four link instant center set, the rear end aligned, the chassis set at the correct ride height, the weight distribution established, the tire rollout established and the tire pressure set. It’s also a good idea to have the Anti Roll Bar (ARB) disconnected while you adjust pinion angle.
It’s easy to see that pinion angle isn’t really a geometric jam up. The concept is simply to have the operational angles as close to zero as possible while the car is under acceleration. Nothing more. Nothing less. Follow the advice from the experts and you’ll not only get “hook,” you’ll also put more power to the ground. And you’ll do it reliably.
This is what pinion angle is all about. In essence, what you’re doing with establishing pinion angle is to ensure that the universal joints angles run as close to zero as possible while the car is under acceleration (see the next illustration).
While the car is under power (no matter what the rear suspension format), this is what the pinion angle should look like.
With something like a race style four link setup, Bickel suggests that you begin with the pinion adjusted so the nose is pointing down -1 to -2 degrees while the car is static.
With a triangulated four link, such as this setup from TRZ Motorsports, the upper bar adjustment on a triangulated four link is used to set the pinion angle. The upper bar is also used to center the rear end (from side-to-side) in the car. FYI, TRZ suggests a setup such as this be set with a static pinion angle of -1.5 to -2.5 degrees (pinion pointing down).
With a leaf spring suspension, wedge-shaped shims such as these examples from Cal Tracs are used to adjust the pinion angle. This is a 2-degree model.
