I have an 89 k-5 blazer with a 350 and 3 inch lift with 33X12.50X15 tires on it. My question is this, I had the u-joints replaced around 6,000 miles ago and they are going bad again on my rear drive shaft. Does anyone have any idea why they may be going bad so early? Any help would be appreciated. I had them put in by a mechanic and i keep them greased also
Did you lower your tcase after the lift? There are two spacers on the bolts that mount the crossmember to the frame. Move them so they are between the crossmember and frame so the case is lowered. Also, do you have shims under the rear springs? These things will help you get better angles and make your u-joints last longer.
Do you have a lot of axle wrap? I've notice some older pickups are starting to get the infamous pinion-down syndrome.
By any chance is your frame bent or "dogtracking"? You should be able to look from the back of the truck at your transmission and be able to imagine a straight line between your crankshaft and your pinion shaft. If it isn't straight it can cause transmission cases to break and universals to wear out.
My 1982 K5 use to eat U-joints ALL the time. The problem with my truck turned out to be a bad pinion yoke on the rear axle. One of the U-joints that blew lost a cap on the yoke side and the torque of the driveshaft drove the inside bearing surface of the U-joint into the yoke, putting a hell of a divot into the yoke itself. I didn't notice this right away... I'd get a couple thousand miles on the U-joint, then KA-BAM! I finally saw the dent when I was replacing a U-joint. Replaced the yoke and problem fixed.