I've been very slowly making progress on my center crossmember throughout this entire build. It started with flipping my trailing arm mounts to help correct pinion angle and limit the downstream effects of lowering my rear end so much. Then I eventually cut the 4.5" holes to allow for the exhaust pass throughs. Then I added the reinforcing hoops to strengthen the holes I cut. Through all this, I kept noticing how low the center of the crossmember actually hangs below the frame rails. Additionally, the front scoops down and would make for a very bad day if it were to catch on something. I decided I needed to flatten the bottom of my crossmember. I know I've seen it done before, but for this mod I decided to skip the forum research and do it on my own. I wanted to flatten it such that it was no longer the lowest part of the frame. I was able to get it high enough to where it's level with the bottom of the rivets holding in the crossmember.
You may have noticed the tab hanging off the rear of this plate. That is my integrated carrier bearing mount. On my other truck, I had to flip the carrier bearing mount from top to bottom so I could raise the bearing up to correct driveshaft angles. This is a consideration that must be made when lowering this much with a two piece driveshaft. I like to keep the two piece because it helps with clearance under the cab. I figured, since I'm going through all this work I might as well make the mount part of the crossmember.
At this point, I was able to do all my driveshaft measurements. First was length. I determined the stock driveshaft will work if I shorten the front shaft 3.25". I will leave this task to a professional driveshaft shop. Next up, driveshaft angles. Starting with the engine, it is at a fixed -3.7 degrees. I can't change that because my clearances are already tight enough to the cab. That means driveshaft 1 has to either be -4.7 or -2.7 degrees (1 degree difference from engine). If I go -4.7, that means my pinion has to be -4.7 as well, which puts driveshaft 2 at +4.3 degrees. That results in 8.9 degrees on the universals which is unfavorable. The -4.7 option was appealing because I could bolt the carrier bearing directly to the mount with no spacers. The -2.7 degree option requires a 1/4" spacer to reach this angle. Not a big deal though. This gives me an angle of +2.3 degrees on driveshaft 2 and a universal angle of 5 degrees. This is much more acceptable. In order to achieve this on the rear end, it must match driveshaft 1 and therefore needs to be -2.7 degrees. Bolted straight to the drop blocks, the rear is at -6.7 degrees, so I will need to add some 4 degree shims and it will be perfect.
While figuring all this out, my little helper was very confused.
