Join Date: Aug 2014
Location: Grosse Pointe, MI
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Caster angle and pinion angle are zero sum. When you increase one, you decrease the other. The axle C (inner knuckle - the part people gusset all the time) tilts back like the fork of a bicycle. That is your caster. Imagine riding a bike with a fork that points straight down. Steering would be terrible and the ride would suck. Same with a Jeep. No caster and your steering would be erratic and every bump would hurt.
Given that the C is welded on, as you tilt the axle back to increase the caster, the pinion of the axle begins to point further down. So, increase caster 1* (i.e. lean the axle back 1*), and you lower the pinion 1*.
It is a tough balance on a lifted JK. With more lift, you want to increase the pinion angle so there is less driveshaft angle. However, lifting also reduces the caster (as a result of the upper arms being shorter, it rotates the axle forward). So, most people increase caster and decrease pinion. Overall, the geometry is much less than ideal.
Now, what does the 10* prorock housing mean? As noted, the caster relative to the pinion is static. They are separated by 6* on a stock housing. That means that if caster is 3*, then pinion is 3*. Now, follow the math. If I increase caster to 4, then the pinion goes to 2 (again, increasing caster means the axle is rotated back and the pinion decreases in angle). 5* of caster means 1* pinion. And so on.
The prorock comes in 8* and 10*. So, with your 10* housing, if you have caster at 5*, pinion will be 5*. 6* of caster and pinion is 4*.
As far as your setup, I'd definitely go higher than stock in terms of caster. Why not improve the ride and handling a bit? 5* seems to work really well. Might even try a little more. Just make sure your pinion isn't rotated so much that it has more angle than the driveshaft.