# When installing air ride suspension how is pinion angle set on the axle?

Saw we had a Motor Vehicle Stack and I thought it would be fun asking some hot rod related questions. One issue I've always faced in building a hot rod truck is determining how the pinion angle should be set up for the rear end.

So when building a '57 Chevy how should the pinion angle be set?

Should the pinion angle, regardless of ride height, be exact to the yoke of the transmission on a single driveshaft?

Are you allowed a degree of tolerance if the axle and yoke do not match?

The problem is with unequal length arms (assuming a 4-link suspension as we were discussing in chat), the pinion angle is going to change as it travels through its arc of motion. You can see it in this graphic what I'm talking about.

Due to this you are not going to be able to set it for every ride height. Since your application is not for racing, you want the difference between the drive train angle (engine/tranny line) and the pinion angle to be zero. Since you cannot readily set the drive train angle, it's left up to you to set the pinion angle.

Even if your links are equal length, the pinion angle is going to change.

While 2.09° is not a huge amount, you can probably tell from the image that the longer the links, the less the change is going to be in both pinion angle and in wheelbase.

On Mark Williams' website, he says:

Operating angles in a driveshaft are the angles between the pinion, driveshaft and transmission centerlines. The optimal angle for any driveshaft to run at is 1/2 degree, where many vibrational and frictional problems are non-existent. In order 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 racing applications should 2 degrees and the centerlines should be parallel within 1/2 degree. With suspension movement the operating angle will increase, but should not exceed 15 degrees. If the centerlines are off too far, the u-joints travel at uneven operating velocities, causing vibration (this is the same problem induced by poorly phased end yokes). This vibration is hard to distinguish from an unbalanced driveshaft.

Due to all of this, your best bet is to set your pinion angle at your driving ride height. This will allow you to drive at highway speeds without worry of driveline vibration. It will also still allow you to get around if you want to move your vehicle when the ride height is raised or lowered from driving ride height.