cdherman
Active Member
The discussions here might be a tad off -- as far as I know, the 03-05 series has an electric clutch in the transfer case that ingages power to the front diff. There is no vacuum in the front diff, but there are vacuum actuators at each hub.
Now, those actuators are made to "fail safe" -- when they lose vacuum, they engage. When the vehicle is in AWD, 4H and 4L, the vacuum solenoid in the dash dumps the vacuum to the actuators and a ring gear slides over and locks the hubs.
So the theory that losing vacuum will cause the hubs to disengage is not correct. When they are engaged, they have no vacuum to start with.
Only in 2H is vacuum applied to them, which sucks an air bladder empty and moves the ring gear over, disenaging the hub. In fact, if you start to hear grinding in the front hubs when in 2H, the first test is to put it in 4H and see what happens -- if the grinding goes away, it means that that you have a vacuum leak or the solenoid is failing.
Anyhow -- back to the original issue -- getting stuck in 5'" snow??? Was there 6" of mud under the snow? Something MUST indeed be wrong. I basically run bald all seasons on my 04 Expy (seldom off road) but I have turned a round or two in my pasture with 10" of snow and didn't get stuck. I do have limited slip rear though...
I would indeed be concerned that one or both of your front hubs are not locking in, OR the electric clutch in the transfer case is not working. Can you see one or both tires spinning up front? Front axel is NOT a limited slip diff, so one spinning is probably all you will get. But at least one should spin.... The vacuum solenoid (somewhere up front in dash, though I hve never seen mine) is reputed to fail in various ways. Perhaps it is stuck open and refuses to allow the vaccum to dump and engage the hubs.
You can also pull the vac lines off the hubs, suitably cap the vac ports and plug the lines. Then put her in 4H, in park with engine running and lift ONE tire off the ground. You should NOT be able to turn the lifted tire since the transfer case is engaged and the other tire is on the ground. If you can turn the tire, look and see if the CV shafts are turning. If they are, then one or both of the actuators at the hubs are failing to engage. If the CV on the side you have lifted turns, AND the drive shaft back to the transfer case turns, then I *think* that means the clutch in the transfer case is not engaging.
On caveat -- one thing I am not 100% certain of is the transfer case electric clutch in park. Its possible it disengages when in park. I *think* so long as the engine is running, its engaged in 4h and 4l (it engages only when the computer detects slip when in AWD). But I just might be wrong here too.....
Good luck. If the electric clutch in park issues emerges as possible, I will go read in the shop manual for my 04 for you. They are nearly the same...
Now, those actuators are made to "fail safe" -- when they lose vacuum, they engage. When the vehicle is in AWD, 4H and 4L, the vacuum solenoid in the dash dumps the vacuum to the actuators and a ring gear slides over and locks the hubs.
So the theory that losing vacuum will cause the hubs to disengage is not correct. When they are engaged, they have no vacuum to start with.
Only in 2H is vacuum applied to them, which sucks an air bladder empty and moves the ring gear over, disenaging the hub. In fact, if you start to hear grinding in the front hubs when in 2H, the first test is to put it in 4H and see what happens -- if the grinding goes away, it means that that you have a vacuum leak or the solenoid is failing.
Anyhow -- back to the original issue -- getting stuck in 5'" snow??? Was there 6" of mud under the snow? Something MUST indeed be wrong. I basically run bald all seasons on my 04 Expy (seldom off road) but I have turned a round or two in my pasture with 10" of snow and didn't get stuck. I do have limited slip rear though...
I would indeed be concerned that one or both of your front hubs are not locking in, OR the electric clutch in the transfer case is not working. Can you see one or both tires spinning up front? Front axel is NOT a limited slip diff, so one spinning is probably all you will get. But at least one should spin.... The vacuum solenoid (somewhere up front in dash, though I hve never seen mine) is reputed to fail in various ways. Perhaps it is stuck open and refuses to allow the vaccum to dump and engage the hubs.
You can also pull the vac lines off the hubs, suitably cap the vac ports and plug the lines. Then put her in 4H, in park with engine running and lift ONE tire off the ground. You should NOT be able to turn the lifted tire since the transfer case is engaged and the other tire is on the ground. If you can turn the tire, look and see if the CV shafts are turning. If they are, then one or both of the actuators at the hubs are failing to engage. If the CV on the side you have lifted turns, AND the drive shaft back to the transfer case turns, then I *think* that means the clutch in the transfer case is not engaging.
On caveat -- one thing I am not 100% certain of is the transfer case electric clutch in park. Its possible it disengages when in park. I *think* so long as the engine is running, its engaged in 4h and 4l (it engages only when the computer detects slip when in AWD). But I just might be wrong here too.....
Good luck. If the electric clutch in park issues emerges as possible, I will go read in the shop manual for my 04 for you. They are nearly the same...
