I am going to have my car up on a lift insulataing my starter and wiring. While up in the air I want to check my driveline comonents,what should I look for.Also after reading a post on the differenal I think that I will change the fuild.(Don't know when this was last done.)The GM additive that was mentioned do you get it from a dealer or dose it have to be ordered

  Rick

You should still be able to get the posi additive from the dealer. Get two bottles.
Just do the basic things...check for leaks, of course, and make note of anything that needs attention.
It's really hard to check U-joints on a Shark, since the driveshaft is pretty much non-accessible, but it doesn't hurt to try. Grab the front of the shaft by the trans, and see if there is any up/down play in it. There will always be a small amount of play, but you shouldn't be able to move it up enough for it to lose contact with the seal. I see them all the time that will move enough for it to start leaking just by holding the shaft up. If the trans is leaking there, that will be a hint of why...too much play. This would be a bushing/yoke problem.

It is impossible to check the rear half-shaft u-joint with the car in the air, unless it is on a drive-on lift. You can however, look for tell-tale signs of u-joint problems, such as rusty trails around the caps where the seals are.
Check the front end carefully for anything that is loose, such as fasteners for the tie-rods, shocks, or control arm bushings. Grab the idler arm where the steering link attaches and push it up/down. You should have no more than 1/4" of movement.

You really just want to look everything over, and see if anything sticks out as needing attention...mostly leaks, damaged stuff, and loose stuff. An under-car inspection can take several hours, if you get too involved, so depending on how much time you have, start with the basics. Adams' Apple2008-05-20 05:11:14

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Joel Adams
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"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

I had my car on a friends lift yesterday checking things out and noticed that the "half shaft" (not sure if that's the correct term) seals were were leaking and doping had been slung out.  The rear end was only half full when we checked the level.

Hey RNB,

 Are you saying that I should top off the diff fuild and just add the addtive to it. As of now I don't have any leaks with the diff( no spots on the driveway)I will check both the dealer and covette shops.

   Thanks: Rick

          

Hey Rick, In my case I used a hand pump and got about a quart and a half of old fluid out of the diff. Couldn't get any more than that out of it.

 Thanks again to everyone ,I like your pump idea Kevin I'm going to give it a try.