Interesting 4WD behavior, 92 PU

These models had issues with front inner bearing lubrication that can cause similar symptoms. One or more of the bearing rollers can stick and spin around the race. The noise is sort of a growl or even whirring noise, and you can feel it too. The inners are only loaded in 4WD. I'd strongly recommend you remove the hubs, outers, and properly grease the inner bearings. It takes a special tool to get the grease into the inners correctly, unless you completely remove them. A buddy of mine uses a piece of pipe that fits over the spindle and forces grease into the inners. While you have it apart, I'd also suggest you replace the auto lockouts with manual.

Thanks for the advice Dan. Though I engage the 4WD often enough for proper lubrication according to the manual it doesn't mean that the previous owner did. I'll check the bearings and properly grease them. The automatic hubs work fine now except for maybe the above condition which is gone now. Why should they be replaced by manual hubs? Thanks, Eric

I think automatic hubs get a bad wrap sometimes. I have had some on one vehcile for 18 years now and they have been no trouble. A mistake some make working on them is over packing them and then they fail in cold weather. Also why you have it apart, replace all wheel and axle seal to get access to regardless of their apperance as they are getting up there is age.

----------------- TheSnoMan.com

The inner bearings don't get lubed at all unless someone takes the time to do it right, so odds are good that yours have never been done. Your description of the noise and the fact that it started and stopped with the use of 4WD sounds very much like that same issue. The addition of new tires is also a possible indicator that they are stressed. I had one that did it only in cold weather, and it was only 3 years old at the time. It doesn't take much to flatten a roller when one sticks, so beware.

Auto hubs get a bad rap because they deserve it. They tend to not be engaged when needed, and also not disengage when needed. It's just something to do if you have the thing apart anyhow, and manuals are cheap.

The requirement of a obscure (and probably $pendy) grease for the auto hubs is another reason to replace them with manual AISIN hubs.

Thanks Everyone for the advice on hubs. When I take the thing apart I'll see how things look and make my decision. Cheers, Eric

Does the truck have auto hubs or an auto disconnecting differential? If it has the ADD option which my 91 does then there is nothing to maintain other than a good greasing of the front wheel bearings and the spline ends where the front drive shafts go into the hub plates. Be careful of those tapered washers when you take it apart, they are under pressure and "pop" out away from the studs. The first time I greased mine I spent more time looking around the garage for those tapered washers than I did actually performing the work. The best way to remove them is to loosen all of the cap nuts but do not remove them. Then use a metric bolt in the two threaded holes of the hub plate to push the plate away from the hub, then back out the two metric bolts you installed and tap the hub plate inward, the tapered washers should all release and stay on the studs. Once you get the entire hub and rotor assembly off of the spindle you can remove the rear seals and bearings, repack the bearings and replace the rear seals. I do mine every 100,000 miles with synthetic grease and so far with 300,000 miles nothing has failed. Replacing them with manual hubs would just be redundant unless you replaced the ADD differential with a constantly engaged one.

I disagree with that. Switching to manual hubs will save wear on your cv's and some other stuff as your driveshafts won't be spinning all the time. I also just disconnected the the vacuum line from the ADD dif so that it would not disenage and I've had no problems since. Everything seems to work as if I had a full manual system. I think I had the exact same problem as the OP. I'd just bought the truck so I just took it to the shop and it cost $500 bucks to fix.

Cheers,

-Andrew

Reality check: There's virtually no wear on shaft bearings and CV joints unless the unit is in 4WD.