GMC Other

98 Chevy S-10 Xtnd Cab, 110k miles, Vortec 4.3 L. 2WD. Primarily highway miles

Still trying to fix a problem that I think started 3 months ago. Replacing the front brakes, resurfacing the rotors, and repacking the bearings seem to eliminate a humming I thought was coming from the front driver's side wheel and/or tire; replacing the driveshaft bearing support (Is there more than 1?) Seemed eliminate a squeaking, rattling sound that replaced the humming. Now there is a thumping /low frequency knocking coming from underneath, about mid cab, that I hear and feel only in drive, and greatly reduced in reverse. I can rev the engine in neutral or park, and I do not hear or feel it. If I take my foot off the gas I can barely feel it or hear it; it seems to slow down the same as the speed of the truck. The vibration I feel from the floorboard and through the pedal has been getting worse since the humming originally started. So far, I'm out $1200.
Now I'm being told by a new mechanic that it's a bad differential joint of which there are five, and that if I replace even one of them, the driveshaft will be need to be taken out to shop for balancing. I've only found a few references to this " balancing" of a driveshaft in the existing posts and I can't find a diagram of the driveshaft assembly anywhere. Is this balancing really necessary? The understanding I have is that the joint itself is knocking around inside the cap (somekind of housing?) Because the grease it is normally packed with has leaked out somehow. How long do I have before doing more damage? I get the impression this could lock up in the next 5 days or 5 months or years depending on how easy I am with it.

What can you tell me about this? I understand worse case scenario, all 5 needing replacing, it'd be an all day job and about $475, but he thinks it's only one. Thanks for anything you can illuminate about this.
February 19, 2006.

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