Hot Rods caster and pinion angle question.

I acquired a stock 36 Ford pickup several years ago that is complete minus the engine. It's setting in the corner while I collect parts for a build after I complete several more projects so it it will be another few years before I can tear it apart and do it right. I just acquired a 36 flathead and considering putting the engine in the pickup and maybe driving around town as is. Someone has already put hydraulic brakes on it. I plan on lowering it 3-4 inches in front and back and the question is, how will this affect the caster on the front with the stock wishbone and the rear end with the stock torque tube? Will I have to adjust either after lowering? Pie cutting the wishbone up front is the only way I see to adjust the front caster and have no idea on the rear.

 

Depends on how you wish to obtain your drop, what is your plan?

 

dropped axle and maybe spring up front and spring and possibly altering the rear cross member.

 

If you're dropping the rear, might as well drop the front with another axle or get yours dropped. How do you plan to drop the rear, flatten cross member or de-arch spring. Either way it would make no difference as there is no pinion angle due to torque tube and radius rods. If you drop it shocks may require some adjustment later to ensure adequate travel. I presume they are original and not tube shocks? As the tailshaft is enclosed, there is no flex along the length, the pivoting is done at the ball at the rear of the transmission. If you make it an open drive line you would then need to consider your next move to align things and also add torque rods to the differential forward to connect with radius rods as OEM bones are too weak by themselves. Are you going to keep the OEM wishbones or split them?
If front and rear suspension are dropped equally the caster would be not be affected that much. You may gain a degree or something minor. Keep it roughly 7 degrees on the front and it'll drive straight and turn as expected. As long as your suspension travels and there is no bind you'll be fine.

 

I will dropping the original axle in front and I can see that will not change the caster but if I also go with a Posie reversed eye spring, I think this might change the caster. I'm not splitting the wishbone up front.
All mods will be to the front axle, springs and possibly the flatten the rear cross member if I can't get a Posie type spring in the rear to get it low enough. I guess if the torque tube only pivots up front on the transmission I won't worry about that and I assume there won't be any spring binding in the rear. I'll be using original shocks and will adjust as necessary.
Thanks for the advice.