Understanding our Two-piece Drive Shafts

I'm having troubles understanding our two-piece drive shaft angles. I'm documenting the stock angles in an effort to work out any problems I may have with mods in the future, suspension additions and lifting the truck. I'm reasonably well versed in one-piece drive shafts, with and without double cardon joints, as I have run both of those configurations in another vehicle. This two piece has me scratching my head as to why the particular angles?

I've watched a few videos and read some tech documents to no avail. I'm just not understanding the angles and how the two shafts relate to one another.

Spicer has a drive shaft configure app, with no explanation of why the angles? The app seems to be designed to measure U-joint operating angles, so no one exceeds their design limitations.
Driveline Operating Angle Calculator | Spicer Parts

Vehicle is an 4x4 Access Cab, Long Bed, Off Road. I believe the running gear length is the same for the much more prolific Double Cab, Short Bed trucks.

On very level ground, all angles are stated as "angled down" towards the rear of the vehicle as that was the only principle I garnered from the videos and tech documents:

Starting at the transfer case the flange is angled down 3.1 degrees
The first short section of drive shaft is angled down 5.8 degrees
The body mount for the Center Carrier Bearing is angled down 5.9 degrees
The second longer section of drive shaft is angled down 4.7 degrees
The pinion flange is angled down 5.1 degrees.

Sorry, no drawing capabilities.

There is also an ~2-degree pinion angle wedge between the rear springs and the axel perch angling the pinon, without this wedge the pinon angle would be ~7 degrees down. The thick part of the wedge is towards the rear, and the thin part is toward the front of the vehicle.

Measurements were taken with:

iGaging Digital Angle Cube Guage Bluetooth Bevel/Level/Protractor Magnetic Panes Lighted XL LCD

iGaging Digital Angle Cube Guage Bluetooth Bevel/Level/Protractor Magnetic Panes Lighted XL LCD: Amazon.com: Tools & Home Improvement

It is a stock vehicle with no rear suspension work. Only weight in the rear is a shell (~200lbs) and maybe another 100lbs of miscellaneous. ~300lbs total.

Any help with the theory of two-piece shafts? In an easy-to-understand language.

Future additions will be a crawl box which will shorten the first short rear drive shaft by ~9". Plus, some sort of suspension and lift after that.

I plan on shortening the short drive shaft when I do the crawl box and possibly going to a one-piece drive shaft with the suspension work or lift. Those plans may change.

My only thought is that somehow the carrier bearing is acting as a double cardon as the rear shaft is basically straight into the pinion. As it would be in a one-piece shaft application using a double cardon out of the transfer case.

I have searched here on TW and found no discussion of this topic. If there are any good threads, please direct me to them.

Awaiting GREAT information!

 

The front half of the driveshaft is considered an extension of the transfer case. It is not an exact extension of the transfer case based on the fact that it is angled a bit down from the transfer case, but that is for various reasons such as lubrication of u-joints and tweaking the rear half angles.

The rear half is treated like a standard 2 joint shaft. Angles mostly parallel.

When you do the crawl box, you will probably want to do a 1 piece driveshaft. The reason being the drivetrain is angled down already, and you will be eating up that 9” of the front half, making the front half really short and throwing its angles off. The angles will be off because the angle of the drivetrain will put the transfer case flange closer to the ground than it is currently, which will tweak the angle of the front half and then correspondingly throw off the rear half as well.

 

The stock driveshaft is two-piece because it would otherwise have too long of an unsupported span and approach its critical speed. This is why shorter-wheelbase models like the 4Runner and FJ can get away with a one-piece driveshaft, and without a double cardan joint. With a crawl box, you would probably be able to get away with a one-piece shaft as well.

 

I found this forum post helpful. The screenshots in that post are from this website, which I would recommend reading:

https://www.4crawler.com/4x4/CheapTricks/Driveline-101.shtml

After installing new leaf springs with 3" of lift I checked to see how parallel the transfer case flange angle was to the pinion flange angle. Using an angle finder I zeroed it on the transfer case, then found the pinion flange to be 0.5 degrees off. Closer to zero is ideal. If the angle was 1 or 2 degrees I would have used a shim between the rear axle and leaf spring to get it closer to zero. Sometimes further adjustment of the carrier bearing is needed, usually by adding small washers between the frame. I had no vibrations at hwy speeds so I did not adjust my carrier bearing.

 

You guys sure think a lot about shaft angles!

 

I feel like your baseline is flawed because they are against an imaginary level plane when the truck could be sitting differently on the suspension and that would impact your angles. Should you measure of of something more constant to the vehicle like off of the frame? Then regardless if the vehicle is pitched nose down or ass down a little your angles should be consistent. Or am I missing something?