Drivetrain angle with unknown aftermarket lift

[vrtillman]

I'm under my tj this morning and finally discover why the fan shroud on my jeep sits funny and my shifter seems too short. I just bought this 98 TJ and it has a "custom" long arm lift installed. Basically they took the existing trans/t-case crossmember/skid plate and dropped it to make room for the "subframe" that has the control arm mounting points. The trans mount installed currently looks to be aftermarket (based on what I'm seeing online) and thus smaller and so the whole engine/trans/tcase combo is at a weird angle. Unbolting the mount and raising the combo by ~2.5" seems to be the sweet spot for where all this stuff should be sitting stock (this is just an eyeball, i have nothing to confirm this, that's why I'm here). I want to make a spacer that goes in between the trans mount and the crossmember/skid plate but I want to make sure I'm not getting any of the driveshaft/pinon angles wrong. Can anyone provide the measurement for what the rear pinion angle and transfer case pinion flange should be?

I also have some concern about the rear driveshaft. The drive shaft slip yoke seems to be sticking out kind of far when I have the drivetrain lifted and the double cardan joint seems like its close to binding. I just want to make sure I'm not gonna screw this stuff up

Pictures for reference

gap between top of trans and trans tunnel as it currently sits

t-case pinion flange as it sits at the funky angle

current rear driveshaft slip yoke

current driveshaft angle

proposed "new" gap between trans and trans tunnel

"new" 2.5" gap between trans mount and crossmember

how the cardan joint would sit

how the slip yoke would sit

the "new" angle of the transfer case pinion flange

"new" driveshaft angle

 

[sierradmax]

Based on the pictures and the angle of the long-arm control arms, that Jeep has a lot of lift and was compensated for a T-case drop. The pictures are very small and one cannot help you without written values of the angles in description. Technically, with a double cardan driveshaft, the pinion angle should be a degree or two lower than the driveshaft at ride height... I.E. if your DS angle is 20*, shoot for between 18-19 with the pinion. Based on picture 4, it would appear the angle is much greater and the pinion needs to rotate up. In doing so, adjusting the UCA's would help but I think your end goal is a Tummy Tuck?

Also, maybe someone can chime in but is that an aftermarket flange for a 231? A SYE might push the centering ball of the double cardan further forward, reducing the DS angle a bit.

 

[AjRagno]

That rear pinion angle is way too low.

View attachment 253930

 

[vrtillman]

Sorry, I forgot to put the initial readings:

As is (drivetrain at weird angle):
Rear axle Pinion Angle: 8.5 deg
T-Case Output Flange Angle: 12.5 deg
Driveshaft angle: 22.5 deg

With Drivetrain lifted back to neutral position:
Rear axle Pinion Angle: 8.5 deg
T-Case Output Flange Angle: 7.5 deg
Driveshaft angle: 34 deg

I kind of assumed I'd have to adjust the read axle pinion angle if i reset the whole drivetrain to this new height/angle. As of now/when i discovered it, the whole engine/trans/t case assembly is tilted down toward the rear of the jeep, basically hinging on the engine mounts and i want to fix that. the "subframe" that the control arms are connected to does act as a transfer case drop, but it puts my fan/shroud and my shifter at a weird angle and I'd like to fix that if possible