OK I have looked and found all sorts of threads on measuring drive shaft anlges and what not. But my question is if i have a stock rear suspension and add 2" lift shackles(as in adds 2 inches of lift) do i need to shim the axle.. and if i do, how many degrees does it need to be shimmed. Please don't refer me to the roger brown site, i have been there and i am just curious as to one paticular instance..

 

its fine the way it is.... i actually have a 2" tall ahckle in the rear and asked roger about it recently, when i was over at his house.... he siad its not a big enough deal with the stock springs with just 2" shackles..... i will eventually be doing an soa on my truck and that time i will have the new perches welded on and correct for any angle.....

 

ok sounds good... i already have spring over... but looking at the axle it seems tilted back quite a bit... like it almost seems like i can't get the same amount of fluid in there as before.. thanks for the info!

 

You'll find the answer on my shackle page:

http://www.4crawler.com/4x4/ForSale/...es.shtml#FAQ12

As noted, you'll see about 1 degree of pinion tilt per extra inch of shackle. Since a 2" lift shackle is likely about 4" longer than stock:

http://www.4crawler.com/4x4/ForSale/Shackles.shtml#FAQ4

You would need about a 4 degree shim to correct the pinion angle, assuming of course you have a single cardan rear driveshaft:

http://www.4crawler.com/4x4/CheapTri...line-101.shtml

If you have a double cardan rear shaft, then the angle changes usually cancel out to some degree. You increase the shaft angle with the shackle lift but at the same time you are tilting the pinion up to compensate for the increase shaft angle.

Of course the best answer is to measure the driveshaft and u-joint angles before installing the lift (assuming that was working fine) and then install the shackles and meausre the angles again. If you experience vibrations afterwards, then compare the angles (before and after) and get a shim made to restore the angles to the way they were before:

http://www.4crawler.com/4x4/ForSale/Shims.shtml

 

ok i think i got it... there isn't any really bad vibration... and since it isn't my daily driver i won't notice it till i drive it a lot...thanks for the info guys

 

That is essentially the last option I listed, IOW "if it ain't broke, don't fix it", or if it drives OK, don't change anything. Driveshaft vibes are not something that will instantly cause the driveshaft to self-destruct (unless they are incredibly far out of whack). You usually have some room to play with as far as angles go. So if you were at one end of that range in stock form and didn't go out of that working angle range with the shackles, then it may still be OK. You may not notice any vibration until a u-joint starts to wear, or you change the lift or do something else to upset the balance.