Front pinion angle

[Matt99XJ]

What should the pinion angle on the front of an XJ be set to? I know that in the rear it should be 2* below. In the front is it 2* above?

[MaXJohnson]

The rear pinion is expected to move a degree or two because of leaf spring wrap. Under power, reactive forces push the pinion up, so it is common to set it to a static angle slightly down from optimum.

The front is a 4-link/coil setup, so there is very little movement of the pinion. What movement there is depends on the type of bushing material used; rubber, poly, nylon, steel, etc, but it's much less than in the rear for any but Jet-Puffed marshmallows. Besides the design differences, you have to also consider that the front isn't normally under power. If it is, the pinion would have a tendancy to go down, in the more common coast mode, it would tend to lift upward ever so slightly. In either case the change isn't enough to worry about. In a perfect world, you could set the operating angle to 0°. Then whether the axle was under power or coasting, the fractional change in pinion angle would be just enough to exercise the joint ( 1/2° is plenty for this).

In the world we live in, you have to consider the relationship with castor angle. If you change one, the other will change a like amount. At your lift height, a perfect castor angle will result in a poor pinion angle and visa-versa. With this in mind, you need to find a compromise. Try to achieve the maximum castor (within spec) you can that doesn't result in u-joint induced vibrations. This may end up being 4 1/2° to 5 1/2° if you're lucky. Having locking hubs or a disconnect axle makes this a whole lot easier.

[Matt99XJ]

Thanks for the info. I am going to have to adjust it up just a little bit more. I am still getting some annoying vibes when I get over 60+ mph.

[Beezil]

yep.

here's a ditto post.

concentrate on your caster angle, and live with the resulting pinion angle.

it is difficult to compromise in this area.