so a 10* shim will get me all lined up right?
Here's the deal:
Pointing the pinion down will increase the slope of the driveshaft and will increase the operating angle of the pinion u-joint. You can calculate the angles if you wish.
I messed around with driveshaft angle
a lot and in the end the best setup I could come up with is to have ~1 degree operating angle on the pinion side (below center, pointing just below the t-case output) and then whatever angles on everything else (I had a 4" lift with a 465/205).
I hardly ever noticed vibes but the 205 made the common grinding noise while coasting (meaning the vibration was there).
According to Spicer, their joints shouldn't be operated in excess of 3 IIRC because there will be noticeable vibration after that (and that's taking into account that both joints are operating at the same angle).
Basically what that means is that if you are lifting the truck, you will have vibrations unless you go to a cv style driveshaft.
MT, pointing your pinion back down may help and it may not.
U-joint vibration is caused whenever a u-joint is operated at
any angle. This is because each u-joint cap speeds up and slows down through its travel (this is easier to see than to explain). Since there is a u-joint at each side, and if they are phased correctly (your driveshaft should be phased correctly already but you can search to see what I mean), the two vibrations will cancel each other out.
With the pinion pointed further down the pinion u-joint will do a better job of cancelling out the vibration caused by the t-case u-joint. But the operating angle of both joints will be more severe. You will be well exceeding Spicers limit of 3 deg. You may be able to make the vibes better but you won't solve the problem without a double cardan driveshaft.
