help with pinion angle

[makovai]

Ok...so i took all your advice and decided to assemble my 14 bolt without welding my spring perches. I now am to that point and i'm ready to tack the perches. The rear axle is on center within 1/16". But im not sure as to how much to rotate the rear axle for pinion angle. I'm running 6" arched skyjackers with 2" blocks. What the procedure for this angle. I know that i want some angle on the u-joints because the are not designed to run perfectly straight with the mating piece. Although there is a jack in the picture the truck is sitting compressed on all 4 wheels.

 

[Confedneck79K30]

iirc, you want the angle of the output to be within 1.5-2.5* of the input on the axle...

 

[makovai]

iirc, you want the angle of the output to be within 1.5-2.5* of the input on the axle...

Huh?

 

[4X4HIGH]

If you are not running a CV shaft then the T-case output shaft and the pinion yoke need to have the exact same angles. Put an angle finder on the T-case output shaft and measure the angle then do the same with the pinion yoke. Obviously the T-case output shaft will be pointing down and the pinion yoke will be pointing up but both need to be the same angle just in opposite positions.

 

[makovai]

If you are not running a CV shaft then the T-case output shaft and the pinion yoke need to have the exact same angles. Put an angle finder on the T-case output shaft and measure the angle then do the same with the pinion yoke. Obviously the T-case output shaft will be pointing down and the pinion yoke will be pointing up but both need to be the same angle just in opposite positions.

got'cha.... thank you

 

[MattK]

ooooooor some people say to aim it 2* down from being equal with the tcase angle to compensate for axle wrap.

me?...i had the guy that was welding up my perches eyeball it. no vibes with a shackle flip and zero rate, no relocation.

 

[makovai]

I know this doesn't fit quite what we talked about but i'm gonna use this little angle. I'm adding another inch in the rear plus I've got angled shim on the bottom of my springs that i can take out if this isn't enough angle.

 

[4X4HIGH]

Why not measure once and make the corrections the first time?

 

[Hogback Fabrication]

If you are not running a CV shaft then the T-case output shaft and the pinion yoke need to have the exact same angles. Put an angle finder on the T-case output shaft and measure the angle then do the same with the pinion yoke. Obviously the T-case output shaft will be pointing down and the pinion yoke will be pointing up but both need to be the same angle just in opposite positions.

That is the theoretical way to do it. And it works. In theory. The reason you want the angles the same is because the caps of cross style universal joints (the outside of the joint) speed up and slow down as the joint rotates. It actually travels in an ellipse shape rather than a circle. This is what causes a vibration. Since the driveshaft has two u-joints, operating them at the same angle (and hence, the same vibration intensity) will allow the vibrations to cancel each other out (as long as the u-joints are phased correctly i.e. your driveshaft is assembled correctly).

The problem is that we subject our u-joints to much steeper angles than they are designed for. At angles like a K5 with a 4-6" lift (somewhere in the range of 20 degrees at each joint) the vibrations will be so great that even if 90% of the joint's vibration is cancelled out you will still notice a vibration.

My own experience is that I have the least vibration with the diff pointed just below the the t-case output (i.e. my lower u-joint has ~0 operating angle). This also means my upper u-joint has a lower operating angle (15 degrees maybe?) but has nothing to cancel out its vibes.

 

[Hogback Fabrication]

FWIW, pointing your pinion at the t-case output will not work for everyone. That is just what I found to work best for me after changing the angles 3 or 4 times. Just like everything about our trucks, everything about them is different and what works for some will not work for others.