This is basically a 2-part question. 1) What is the optimum pinion angle for my particular chassis, and 2) How do I set it?
Imagine two parallel lines joined by the driveshaft. One line is the trans output shaft, the other is the line of the pinion itself.
Ideally, the angles formed at either end of the driveshaft will be equal and opposite of each other (pinion and output parallel). That represents 0 degrees pinion angle. But the angle changes with both suspension travel and torque. How much depends on your chassis set up.
You can use gauges and other measuring devices to determine the angles. A simple way to do it is put the car on a lift (ideally) or get both ends as high off the ground as you can. Set the output and pinion yokes vertical and insert something like a broomstick in them (it helps to have a spare output yoke). Use some duct tape or something to sleeve it up to where it fits snugly in the yoke. Now step back about 10 feet and just look at it! If the sticks are parallel, you have 0 degrees pinion angle.
Check it with the suspension loaded and unloaded. On Mopars (or any leaf spring setup, for that matter) the angle will begin to go negative as you add weight to the suspension. If you have a stout suspension with something like Caltracs to control spring wrap, you can run as little as 2 degrees with the weight on the suspension.
My Duster for example, is set to 0 degrees unloaded and appears to run at around 2 degrees down with the car's weight on it. Running stock springs with no traction control would require more negative pinion angle to offset the change in pinion angle caused by the torque load on hard launches. Snubbers and slapper bars may mitigate this, but it becomes guesswork at some point.
Running alot of pinion angle to offset a weak suspension is a poor solution, but will work to some extent. Just don't expect it to hook real well, or the u-joints to last very long.
The best way to set it once you determine what you want is to weld the spring perches on at the correct pinion angle for your particular setup to start with. Shims are available to chage the perch angle afterwards, if needed.
Paul
