I think guzzle has tried it before but I dont know about his success or whatnot. Shoot him a PM or email and ask him. Hes a great guy. Pointed me in the right direction to which spray lube to "unfreeze" my auto/manual dial. (DuPont Teflon spray lube)
I have still left the hubs in auto and when I turn the switch on the dash to 4x4 the front drive shaft turns. When I turn it to 2x4 the front drive shaft does not turn. I know this because my wife was driving and I stood outside the truck and watched the shaft. The only thing I have not done yet is to vacuum test each side and make sure that they are both working but i looks like the vacuum latches and unlatches the hubs in Auto as designed. When I took the hubs apart for cleaning I did notice that one latching mechanism was hanging up on one of the two stainless prongs. A little bending with the needle nose made sure that there was no hang up.
If you are trouble shooting if you have the two plastic pieces with the spring inside in your hand, one squeeze should lock the assembly together which would simulate the vacuum and diaphram squeezing the plastic together to unlock the front drive shaft by moving the outer steel gear outboard.
If you squeeze the two plastic pieces together again they should now come apart so that the spring can be removed. This second state of the latch would simulate the vacuum and diaphram squeezing the plastic together to lock the front drive shaft by moving the outer steel gear inboard as the spring expands and engaging the teeth.
Hope I have explained it properly to those who are having difficulty getting their front axles to free wheel in Auto.
Iron, I believe you are the only one here who has asked questions about the internal operation of these hubs. I, too are very curious about how these operate.
You describe an action similar to the ratcheting of a retractable ball point pen -- where one "click" holds the plastic unit together and the next click releases it.
That would be fine, but how does that account for a strong (45 second) vacuum signal latching the hub and a weak (15 second) one unlatching the hub? If the hubs operated as you describe, how would the thing differentiate between a "latch" and "unlatch" pulse?
Anyone else have any thoughts on the internal workings of that little plastic/mental latch?
Trustee, I never thought about the two different signal pulses but here is my guess. The strong pulse is probably to latch and the weak pulse is to unlatch. If for some reason one side does not latch, then the hubs would be out of sync. If the vacuum pulses were the same then the hubs would be out of sync for a long time. With the two different pulses, one to latch and one to unlatch, the hubs could be synchronized quickly.
Some hubs are only automatic. The dial does not turn. If these hubs were out of sync, you would have to take the hub apart and manually synchronize it with the other side. Thats my guess for the two different pulses.
I looked at these things as a challenge on my 2000 Expedition. They weren't locking/unlocking properly.
The first thing I tested was the vacuum source -- and that worked properly.
Then I put a handheld vacuum pump on each hub and found that one was leaking vacuum. It was, of course one that I paid to have the hub bearing replaced.
Well, I took the whole thing apart, cleaned everything up, replaced those very expensive seals, and now it holds vacuum and works perfectly.
The job was easy, if not a little heavy, but satisfying to get the whole thing working as designed.
One thing I should mention is that these things don't engage/disengage immediately. The wheels should be turning while the vacuum is being applied. If you just jack up one side and apply vacuum, it may or may not work. The wheel should be rolling to get a good idea of the performance.
New to the forum so beg pardon I'll jump in. When the auto-lock hubs are set to auto, and the esof switch is set to 2wd, should the axle shafts turn when the truck is moving? The drive shaft to the front diff. is not turning, But the axle shafts are. Thanks in advance for any reply.