Hey ya'll,
I've read a few articles about this but I see almost always non-committal about this subject.
I've built two trucks that were dropped a bit. Neither required a C-Notch but I have a bit of info for the forum regarding both.
First, the leaf spring trucks don't necessarily require any longitudinal redirection for the differential...unless you are going low enough to install a C-Notch or high enough to REQUIRE a redirecton. If you lower, make sure you measure the angles and move on (seek assistance from youtube). the difference in angles should be less than 1 degree but more than 0.5 degrees, optimally.
If, however you have a trailing arm truck, particularly a short bed, you will NEED to check the pinion angle. You see, lowering the truck changes the pinion angle of the differential significantly if you lower the truck. Lowering pivots the pinion angle of the differential proportionately commensurate with the amount of drop. You may be able to get away with a 2" drop but you will have to address a 3 or more inch drop because trailing arm drops will rotate the stock rear gear housing.
For a 4" drop, you will need a 3-4 degree shim. if more drop, you will need a bigger shim. Again, this is only for trailing am trucks (AKA: NASCAR coil spring setup rear suspension with panhard bar).
Note: I have a short bed trailing arm truck...year is irrelevant...lowered 4" rear and 3.5 front. Differential rotated upon lowering. Another is a shortbed leaf spring truck, bagged. The coil spring truck needed shims and the leaf spring truck didn't (differential never rotated).
Hope this helps,
John
