So there I was, driving home from work minding my own business. I hit a bump (more specifically an expansion joint in an overpass), a horrible grinding noise ensues, I hit the next expansion joint on the overpass and the grinding noise ceases. I stop and check, no hot bearings, the driveshafts are tight and it drives normally. Once home I check more thoroughly, jacking up each tire, visually examining all the u-joints, no damage. So I think to myself maybe I oughta try four wheel drive. I back down my driveway, now a solid sheet of ice, and put it in four-wheel drive.........nothing. I try four low.......nothing. I can't imagine that it is the transfer case, or it would not go down the road so well (and quietly) in two wheel drive. As I said, no vibrations no new rattles. I still have the auto hubs (and as soon as I am done typing I am going to put the whole thing on jack stands and see where the problem lies). Has anyone had a similar experience with an auto hub dying? I am really hoping it is not t-case related. They use a lot of salt in Utah and I would hate to have to drive my Jeep to work in the winter (very clean '77 CJ7, no rust and that is very rare for a Utah Jeep). Any advice or past auto hub experience would be nice. Just for info, the Trooper has 284,000 miles and the hubs are original. I have never had trouble with them in the past, but I did just move the mountains and I have to use my four wheel drive at least two or three times a week. I will go check them out and post my findings. Okay, I seem to have omitted some critical information: 88 Trooper, bone stock except for the radio. So I put the thing on jack stands and pulled the hubs apart, everything seems to be in order <img src="/forums/images/graemlins/confused.gif" alt="" />. I have now reassembled and now 4wd works <img src="/forums/images/graemlins/confused.gif" alt="" />. I am at a loss <img src="/forums/images/graemlins/shiner.gif" alt="" />. I know it was not working before because my driveway is slick enough that I could let it idle in 4 low and get out and look. When I looked, only one rear tire was spinning. The front drive shaft was turning, but no front tires were turning. I figure that I will just get a set of regular locking hubs and eliminate the auto hubs as the culprit. It really doesn't look like they are the problem, they seem to engage just as they should, but there really is no other explanation. Any thoughts would be appreciated.