Pinion angle

[Alan Roehrich]

Most people I know run the engine/transmission at zero or a couple of degrees up hill. Then run the rearend a couple of degrees or so down hill. The force rotating the rear end, unless it is mounted entirely with solid bushings or spherical rod ends, will cause it to go from a couple of degrees down hill to close to zero. It will rotate even further in some leaf spring cars.

I don't particularly like running the engine/transmission pointed downhill towards the rearend, although some people seem to make it work just fine. You'll note that the factory often placed shims between the transmission mount and the transmission to raise the rear of the transmission up. I've solved a lot of vibration and breakage problems by simply raising the rear of the transmission a little. I always use a urethane transmission mount, or two worm gear style hose clamps on a good rubber transmission mount, and never use a solid transmission mount.

A u-joint requires a couple of degrees of angle in order to make the needle bearings move, or it will quickly develop wear issues. If the only concern was how efficient it would transmit power, then you would want the u-joints to be at zero while under power. If you did that, u-joint life would be fairly short, and there would be all sorts of vibration and flex problems.

You will never achieve the ideal shown in the Mark Williams catalog with a Stock or Super Stock car. You simply cannot keep the centerline of the engine/transmission and the centerline of the pinion perfectly parallel. If you could, plenty of angle would be created when the rear suspension separated under power.