Suspension / Driveline tech help?

[RckyMntnKng]

Gentlemen,

Need some help understanding my next steps in the suspension and driveline department.

Ive added a set of 6" TC lift springs to my 71 4x4 Jimmy (also 3" body lift), and used a 14bff rear and D60 front. (New perches on the 14bff were installed at the same angle as the stock ones, but moved in to match the new width)

Of course now, the stock slip-drivelines from the 205 wont mount up to the new axles unless there is changes in length and/or universal joint size.

This is where I get confused on my best options....

Do I need a transfer case drop kit?
Do I need to have my drivelines lengthened?
If I do, where are the measurments taken?
Do I need to use a shim w/certain degree to correct angle to the axles?
Do i get a conversion u-joint or better to upgrade the driveline itself to a larger 1 ton matching yoke size?

Someone please steer me in the right direction, it would be greatly appreciated. I want to do this right and have it drive like its 'sposed too when its done.
-RMK

[4x4Poet]

Originally Posted by RckyMntnKng

...Ive added a set of 6" TC lift springs to my 71 4x4 Jimmy (also 3" body lift), and used a 14bff rear and D60 front...

Of course now, the stock slip-drivelines from the 205 wont mount up to the new axles unless there is changes in length and/or universal joint size.

This is where I get confused on my best options....

Do I need a transfer case drop kit?
Do I need to have my drivelines lengthened?
If I do, where are the measurments taken?
Do I need to use a shim w/certain degree to correct angle to the axles?
Do i get a conversion u-joint or better to upgrade the driveline itself to a larger 1 ton matching yoke size?...

Wow!

That's a lot of lift for a short wheelbase truck like your '71 Jimmy. Unless you adore the body looking perfectly stock, I'd trim the fenders enough to either eliminate the body lift for a more stable COG or to lesson the spring lift for both better COG and less acute driveshaft angles. But that wasn't your question. Working with what you have, I'll give it a shot:

Do I need a transfer case drop kit?
Probably not and dropping the xfer case xmember too much would stress the motor mounts some. An inch or two drop probably would be fine. Keep in mind that dropping the xfer case xmember rotates up the front xfer case output yoke (pivoting off the motor mounts) which would create more acute U-joint angles at the xfer case. More likely you might have to notch the xmember under the front driveshaft for suspension droop clearance.
Do I need to have my drivelines lengthened?
No doubt, even though the D60 and 14bFF pinion yokes are closer to their repective xfer case yokes by virtue of the larger pumpkins. Unfortunately, this makes driveshaft angles more acute in addition to the lift. Using a high pinion D60 would compensate for the short front driveshaft.
If I do, where are the measurments taken?
Center cap to center cap. Ton Woods has measurement info and solutions for excessive u-joint angles: 4xshaft.com You'll likely need to go with a CV front and rear. Woods can advise. Your Jimmy is not their first lifted chevy with 3/4 ton axles and an NP205.
Do I need to use a shim w/certain degree to correct angle to the axles?
Maybe, but, on the front axle, only if the shims do not ruin the caster angle. On the rear, any shims should lesson the angle without creating vibration due to imcompatible angles between the top and bottom u-joints. For a radical 4x4, any shims should be steel, not crack-prone aluminum. Too thick shims can create too much pinion angle that reduces the amount of oil that reaches and bathes the pinion.
Do i get a conversion u-joint or better to upgrade the driveline itself to a larger 1 ton matching yoke size?
Yes, match the NP205's rear output yoke size to the 14bFF pinion yoke size. As a benefit, the larger the yoke/U-joint, the more acute the angle it can withstand without binding. They might be the same size. Measure. You need 1350s, minimum.

IIRC, the front yoke size is limited by the front output shaft spline count. The common 10-spline front output shaft can only use a 1310 u-joint while your D60 likely has a superior 1350 pinion yoke. Throw a tape measurer across both to see the difference. 32-spline front output shafts can use 1350 yokes. I'd think the D60 pinion could be changed to a 1310 yoke, but that's going backward in both strength and angle capability.
I think all this also apples to NP205 front output flanges (not a yoke), but seek expert advice. The link above has conversion u-joints but they produce severe vibrations that make them unsuitable for street use. AFAIK, Tom Woods does not hide this fact. They're fine for off-road use only (but not pre-runner speeds). Verify all that, as well.

HTH

[RckyMntnKng]

Wow, thanks for the incredible amount knowledge. Much appreciated!

I will update when I get my angles and drivelines aquired, regards-RMK