I have a fairly stock sammy with heavy duty shackels. But they let me run 31X10.5 without problems. At about 60MPH a shudder develops that feels like it is coming from the rear drive line or the propeller shaft. The U-joints are all in good repair and do not bind. Should I try wedges or having the shafts balanced?????? <IMG SRC="smilies/question.gif" border="0">

Not sure, I've never seen 60. <IMG SRC="smilies/smile.gif" border="0">

I would try the wedges first. If the vibes settle down your good to go. If not check the tranny and T-case mounts, a small twist in the t-case mounts can cause a vibe. I had to go to a CV drive shaft to cancel out the vibration I had after doing my spring over. <IMG SRC="smilies/biggrin.gif" border="0">

Thanks for the info guys, keep it coming. I will try the wedges, I'm just suprised with such little lift I would need wedges but i will try anything <IMG SRC="smilies/bounce2.gif" border="0">

You do not need shims with your shackle lift! Look elsewhere for your vibe. Did you take off the 2 Driveshafts and check for binding? Do not rely on checking them in the rig take them off! Check motor mounts,t-case mounts and tranny mount. Wash all crud from d-shaft and check your weights.
Peace,
Chance.

How long are your shackles? If they are too long they could be causing your problem and shims might help. If they are like 1-1.5" lift shackles they probably are not the cause and you need to look elsewhere.

Ujoint problems usually occr at lower speeds and are noticable under load and decel.That speed would appear to be a tire balance issue.Just to ensure that you checked your driveshafts are in phase right?

I have new einge and t-case mounts. U-joints have been inspected off the vehicle. The shackles are 2 in. When I first had the viberation I have all my tires checked for bent rims and out of balance. I found one bent tim and replaced it. Vibeation is still there. One more twist. With a tail wind the viberation sometimes does not occure at all. With a hard side wind or head wind the viberation always happens and bad. Torque also seem to affect when and how bad??????? <IMG SRC="smilies/confused.gif" border="0">

sounds like a differential problem, like a pinion or more likely carrier bearing.??
vibration is real tough to diagnose though, no telling.

You didn't actually say it, but was the truck vibration-free before you added the shackles? Have you swapped them back off to see if the problem goes away?

I would still rotate the tires & see if there is a change in the situation - it's good exercise & free <IMG SRC="smilies/biggrin.gif" border="0">

You also could set the rear of the truck on jack stands so the rear end is hanging loose- try to move it side-to-side & look for problems.

Did you check out the pinion nut?

[ 09-28-2001: Message edited by: 0ILBURNER ]

Thanks for the ideas <IMG SRC="smilies/bounce2.gif" border="0"> <IMG SRC="smilies/bounce.gif" border="0"> The truck came with the heavy duty shackles. I have have the vibebration since I have owned the truck. I have had one broken engine mount t-case mount and one bent rim. I have replaced all of them. I have inspected the the axle bearings and the pinion bearing when I put in my locker. The only thing I can't check is the preload on the pinion. Keep the ideas coming. thanks <IMG SRC="smilies/smile.gif" border="0"> <IMG SRC="smilies/wink.gif" border="0">