I was pulling a stump out earlier today in 4x4 low and everything worked normally and did exactly as expected. So I go to leave and had already clicked back over 2wd as I didnt think I would need 4x4 again. Well turns out I couldnt make it up a ledge in 2wd, so I click back over to regular 4x4. Relays start a clickin, I hear the case lock in ect. Get up front tires over the ledge fine, and as the back start up, the truck quit pulling in the front. Then as the rear started slipping, it decided it would go back to being 4x4 again. And with a loud thud it started pulling again. Ideas?

 

blew your hubs out?

 

well its not like it wont work now. It went back into 4wd and worked fine. It was like a split second thing. So I dont think anything blew. It was just like it disengaged then reengaged.

 

Would be nice to know what year it is to be able to answer the question.

 

sorry its a 99 with the 5.4 and eletric 4x4

 

The center axle disconnect on the front axle probably hadn't fully engaged. If the lockup collar and the splines werent' fully engaged, when you gassed-it, they spun, then when you stopped, they engaged and all was well with the world.

If it only happens this one time, I wouldn't sweat it. If it happens regularly, I'd look into it.

Also, IMHO, it's a good idea to roll a bit to make sure it's engaged before gassing it. I can tell when mine engages... throw the switch, there's a couple clicks as the t-case spools up, synchs shaft speeds, and engages the lockup collar, then about 5 seconds later, there's a second click that indicates the CAD has locked-in. I hear it, but people often wonder why I'm waiting and what I'm listening for. When I do that, I haven't goosed it before it's fully engaged.

 

I think your right GIJoeCam

 

X'2
I've done it as well a few times with my 99.It just wasn't fullyu engaged and when put under stress slipped and then the thud whas it fully locking in.These systems work best when moving and engaging 4wheel drive versus engaging while sitting still except of course when going into 4lo.I'm sure you didn't mess anything up but put under the right circumstances you could.

 

You should only engage 4x4 when your axles are spinning at the SAME SPEED so the gears can mesh correctly. The back spinning and the front not is what did it and that is certainly not healthy for your drive line Just make sure to stop next time before engaging 4x4 and you will be ok and so will the truck

 

im not stoopid. I was stopped. There is no way I would throw it into 4x4 if I was spending the rear tires.

 

Sorry I swore you said that the rear was spinning and you threw it into 4x4 my bad. Could have been the vacuum line loosing vacuum for a second or two causing the front diff to disengage???

 

no the rear started spinning from the front deciding to to quit working. It was a split second thing. So maybe its a bad vacuum line.

 

The vacuum motor has a duel diaphragm. The actuator rod that is connected to the diaphragm gets pulled in both directions. The disengage side pulls the rod out of the motor housing pushing on the shift fork. The shift fork then slides the lock up collar off the splines of the passenger side axle. When you engage 4x4 the disengage side vents vacuum and the engage side sees vacuum and the rod pulls the shift fork and slides the collar onto the axle. If the disengage side failed to fully vent the vacuum then it may have been enough to allow the collar to slide off the axle when you needed it. You may also have a slow leak in the vacuum lines or the solenoids are defective.

JMC