F-350, troubleshooting 4WD problem
 

I did a bunch of searches and couldn't find my problem mentioned so I was hoping to get a little insight.

I have a 1992 F-350 Crew Cab, 4WD, manual hubs. When I put the truck into 4 high and move whether in fwd or reverse I get a loud thumping sound almost like when turning in 4wd on dry pavement but much louder and the thump moves the whole truck, almost like I'm running one tire on railroad tires or something. The faster I go the louder it gets but have only gone about 25 mph to see if it would go away and it doesn't.

If I unlock the hubs and keep it in 4 high when going forward I get this clicking noise, almost like a ratcheting type but slower and louder. It seems to disappear when going over 25 mph but comes back quickly when slowing to a stop.

I had a guy look at this at the start of the summer and he told me driveshaft and cv joint and he could order me one for $600. A little steep and I'm not really buying his diagnosis but he might be right. I looked under there and nothing appears to have much play or wiggle. I read somewhere before about troubleshooting 4wd and the things to look for with hubs locked and unlocked but couldn't find it. Anyone have a link or an idea what my problem might be?

Thanks,

Hoog

its possible that the axle u joints, or front driveshaft u joints are frozen or worn, i would take them out and check the axles, or driveshaft out and check the u joints and see if they move easy or not, if thy bind up replace them and see what happens, they are in a bad location, they are always getting sprayed with stuff and arent always being used, so i would start with my front axle joints.

yup. sounds like the front driveshaft ujoints are bad. pull the front shaft out and try it again. if the noise goes away it is the ujoints. if it is still there, unlock one hub and try, then relock that one and unlock the other hub.this will tell you if it is a front axle ujoint. if one axle joint is bad, i would change both of them as the other will most likely go soon to