[SCOTI]

Sorry for the delay in responding but I was away for a family emergency.

The discussion about the operating angles needed is accurate but there is a major caveat when dealing w/aggressively lowered vehicles that we need to keep in mind.

From what I 'learned' during the quest for knowledge in this subject area is the 'correct' set-up that is industry standardized has the engine/trans pointing downward slightly (toward the ground) & the rear-end pointing up slightly (toward the sky). In this configuration on normal vehicles, the driveshaft/s would be higher in the front (@ the trans output end/s) & lower in the rear.

When your vehicle fits these criteria, the industry standard for the math calculations used when determining the driveline angles works.

But, on aggressively lowered vehicles (where the rear end is at or above the original frame rail placement), w/the engine/trans output pointing down slightly & the rear pinion pointing up, the math is backwards when doing the calcs because the calcs are assuming the rear-end pinion is lower vs the trans output.

Typical math might be:

Engine/trans within the frame rails & pointing down @ 3°
Pinion below the frame rails & pointing up @ 2°
Rear end housing C/L is 8" below trans output height.

With this scenario, you would look @ it a 3°-2° = 1° difference. This is what you want. The angles need to be as close to zero as possible to minimize vibrations w/o actually being zero for good needle bearing life.

Now take those previously listed numbers but do the math on a vehicle where the rear end housing C/L is within the original rail height vs stock ride height which places it way under the rails. That 2° upward angle @ the pinion is no longer subtracted from the engine/trans output angle because it is @ the same C/L or higher. Once that becomes a factor, the angles are added together:

Engine/trans within the frame rails & pointing down @ 3°
Pinion within the frame rails & pointing up @ 2°
Rear end housing C/L is level w/the trans output height.

With this scenario, you would look @ it a 3°+2° = 5° difference. In the extreme drops, the pinion will be close to level or above the trans output heights, so the driveshaft can actually run upward (toward the sky) to the pinion. In these scenarios, one might need to raise the trans output or bring the pinion down to get that target 1° or less angle difference.

All dimensions/angles need to be pulled w/the vehicle @ it's loaded/suspension weighted ride height.
Unfinished vehicles? You can guess @ the set-up to get things in the ballpark but will need to finalize everything w/the vehicle assembled.
*EDIT* Pinion angle 'change' that occurs during extension/compression varies depending on suspension type.

@cornerstone,

I sectioned & raised the hoop on my ECE T/A x-member 2" higher. With my 3" raised rails & frame notch, plus the trans output @ 3° & rear end level @ the pinion, I had .125" clearance on a 3.5" (?) OD shaft w/the suspension fully compressed. It was just a rolling chassis @ that point but I should be able to dial the pinion in easily one the chassis is fully loaded.