Front Driveline Questions?

I need some help to reconsider how I am adjusting my driveline, what angles to use, and what type of driveshaft I should use. If my math serves me right my TC points 5* downward and right now my front pinion points 5* upward. Should I leave this alone and just get a driveshaft with a u-joint on either end since the angles cancel each other out? I don't have a front shaft right now to measure it's angle but it looks over 10*. I know a lot use double cardan shafts up front just like the back but if I rotate my front axle that far won't I have like no caster at all. Basically horrible driveability? Any suggestions or questions just ask!

1986 Jeep Cherokee
Dana 30/35
Newer NP231J TC with HnT
A904 transmission
Rough Country 4.5" lift with bastard pack leafs
Adjustable Upper and Lower control arms

Double cardan shaft is what you want. Finding a compromise between caster and pinion angle is what you have to deal with...

Is there any fancy online calculator to put in the TC and Pinion angles then put how long the shaft is and it will tell you the driveline angle? Or some mathematical equation? Or do I just have to get a shaft made and adjust from there? Basically I'm trying to set my angles right now while I have it mostly apart!

http://www.harborfreight.com/dial-gauge-angle-finder-34214.html Most hardware stores have angle finders under $10.
If the pinion and tc output are 5-degrees off horizontal, as you say, you could run a single u-joint at each end. Ideally, a few degrees out of parallel helps the needle bearings rotate and wear evenly.

Stock front shaft will work just fine. Set it at 0 degrees to the pinion and see where the caster is at. See how it drives and adjust more caster if you want, but then you will get drive shaft vibes... just have to find a compromise you can live with. Or cut and turn your knuckles or get locking hubs...

larsen said:

If the pinion and tc output are 5-degrees off horizontal, as you say, you could run a single u-joint at each end. Ideally, a few degrees out of parallel helps the needle bearings rotate and wear evenly.

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This is what I was wondering but everyone suggests against it. Is it because there is just too much angle on the u-joints themselves?

sheffeyva said:

This is what I was wondering but everyone suggests against it. Is it because there is just too much angle on the u-joints themselves?

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Does your rig have a center disconnect type front axle?

larsen said:

Does your rig have a center disconnect type front axle?

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No it does not!

Check the angle from the front yoke to the transfer case. If it's more than 25-degrees you probably want a cv shaft.

4.5" lift on a 86'

Yup, a standard front shaft from a newer XJ should work as a replacement for the GKN shaft. I would be surprised if it wouldn't. The 87 and newer shafts are all double cardan shafts, so you don't need to worry about driveshaft angles at the TC.

I know you want to set the angles up 1st. Imagine a line between the axle pinion and a point 1" from the TC output shaft, and you should be close to approximating the drive line. With a double cardan shaft, the pinion side points toward the output shaft. As stated above, you may need to make lemonaid between the drive shaft to pinion angle and the resulting Caster. Most setups do not vibrate with a few degrees difference between the pinion and the DS as long as the pinion is lower.

Hope that makes sense

WB9YZU said:

4.5" lift on a 86'

Yup, a standard front shaft from a newer XJ should work as a replacement for the GKN shaft. I would be surprised if it wouldn't...

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Edit: Assuming you have changed the front output from a flange to the yoke style

WB9YZU said:

Edit: Assuming you have changed the front output from a flange to the yoke style

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The TC I swapped in has a yoke style output. But that's any easy fix. I'll just grab a flange yoke while I'm at the junkyard!