Auto Hubs not engaging (manual engage works fine)

[Metalhead]

My auto hubs are not locking automatically anymore. About two weeks ago, I had run the truck in 4hi and noticed some clunking sounds coming from the hubs after I went back to 2wd. Since then, with the truck parked and idling, I can shift into 4hi and can feel that the driveshaft is engaged, but I can hand spin the axle shafts, meaning the hubs are not locking. I can manually lock the hubs however.

What do you think this clunking sound was that I was hearing? At the time, I had thought it was maybe torque-bind. I reversed a few feet, then didn't have the sound anymore. Ever since then, the hubs don't auto lock anymore.

 

[DaveBen]

You have a vacuum leak. Check the hoses going to the back of the steering knuckle for leaks/cracks. 99% of the time one of the hoses is shot. Simple vacuum hose.

Dave

 

[ckamp52]

hope you're that lucky ..i always read that on here so when mine quit working i just knew i had it figured out but nah my whole pump was out

 

[strokepower]

this is typical on the 6.0s.. my 03 did and now my 05...

 

[Metalhead]

I think the vacuum pump is fine, I can toggle between the dash vent, floor, defrost, and so on and the system responds quickly. It's raining out today, and I can't fit into the garage with this truck, so I'll check this over tomorrow. Thanks for the advice.

 

[ckamp52]

oh yeah ur pump is fine then mine would do that or go in 4x4

 

[MONSTERPLOW]

I always swore by "manual" (XL package )all my life .....no problems

 

[DR.Diesel]

stick a vacume gauge on the line going to your hubs.if no vaccume then the vaccume solinoid is bad.

 

[RandyH]

X 2

When mine went, it was the solenoid.

 

[dennisj2003]

Dont know how you drive, or if you use 4 wheel drive to really do some heavy work, but myself and several others here have had to replace several hubs that have busted, the hubs are simple to check, NAPA has the warn hubs for $125, but you wont have the auto feature.
The hub when you take it off, shake the center from side to side to see how much play is there, shouldnt be more then 1/6 inch most, if more that could be the problem, its not busted but worn bad.