Driveshaft Angles - Blocks, Shackles & AALs

I'm not clear on the way different lift options effect driveshaft angles.

I understand that the angle changes with lift because the Transfer Case is moving up with the unibody while the axle height stays the same. What I don't understand is how the amount of change differs depending on how the vehicle is lifted.

What effect do each of the following have on driveshaft angles?
1. 2" block lift
2. 2" Shackle lift
3. 2" AAL lift

I understand how a shim or tapered block can help correct improper angles. Can the design of an AAL or Shackle provide any ability to correct the driveshaft angle?

Thanks

The pinion angle after a 2" shackle is added will be pointed a bit higher. This is because the spring is now lower in the rear. The change isn't going to be much, and the other two options may change the pinion angle slightly as well. No matter what the change at that point, you still need to use degree shims to corect the pinion angle to match the output angle from the t-case if you are using a standard driveshaft.

Just to clarify, it sounds like you saying that lift shackles tend to have more of a bad effect on driveshaft angle than a lift using blocks or AALs? (because they lift just in the rear of the spring)

Am I understanding you correctly?

Thanks

If they have any effect, shackles will lift the pinion slightly. Whether that's good or bad for your angles depends on what your angle finder tells you about the pinion and t-case output angles.

If you have a CV (ok, ok, so it's a "double-cardan and not a true CV joint, but it just takes so long to say "Double-cardan"!) driveshaft, then it will probably be good. If you don't, then it will probably be bad. But nothing that shims shouldn't be able to fix.

QKRTHNU said:

Just to clarify, it sounds like you saying that lift shackles tend to have more of a bad effect on driveshaft angle than a lift using blocks or AALs? (because they lift just in the rear of the spring)

Am I understanding you correctly?

Thanks

Click to expand...

Lift springs and lift blocks raise the body, and so the t-case, but the pinion stays the same. The u-joint angles at the t-case and at the pinion will increase slightly because of the lifted height.

Adding a longer shackle will slightly change the pinion angle, moves it up, since only lowering the rear of the spring will rotate the axle housing a little. So, adding a lift along with longer shackles might leave the u-joint angle at the pinion close to what it was before the lift. This still might not be OK, since the u-joint angle at the t-case is still increased with the lift. If you drive it and there aren't any driveline vibrations, you're good to go. But, if you have even a slight vibration the u-joint angles should be checked and corrected by using the right shim.

Living with some amount of vibration is not a good thing, since it can knock out the pinion bearing.