[bryaneasley]

I'm having trouble w/ my hub lock system. i understand how the vacuum lock works, does anyone have a way to test wether the solanoid, or the hub seal can be tested. my pump runs constintly, so I just un-pluged it for now. I can lock the hubs manualy, but I've got lazy using shift on the fly... /ubbthreads/images/graemlins/smirk.gif

 

[arisley]

If pump is running constantly, plug off one line at a time and it will show you which line is leaking. Test each individual line from there using a hand vacuum pump.

 

[budman451]

If the pump runs continuously without touching the ESOF switch, it is NOT the seals at the hubs or hoses to the hubs. They will only have vacuum when the switch is turned to engage or disengage 4x4. The most common causes for vacuum leaks without touching the ESOF is either the hose under the dash gets kicked and disconnected, or the PVH solenoid leaks to atmosphere. Check and make sure the line is connected under the passenger dash to firewall, and a quick check at the PVH solenoid, disconnect the vac hoses and plug them. If it pulls vacuum and maintains it, it is most likely a bad solenoid. To verify, you can turn the vacuum lines to only connect the vacuum inlet to the solenoid. If the vacuum is lost and no vacuum is present at the port to the hubs, the solenoid is leaking.

Just a quick lesson on ESOF operation(from memory a bit, numbers may be off a bit): To engage, a 15" vacuum is sent to the hubs for approximately 45 seconds, then vented to atmosphere. To release the hubs, a 6" vacuum is sent to the hubs for approx. 30 seconds, then released to atmosphere. While the release vacuum is applied, it will not unlock the hubs until that vacuum is vented.

Buddy

 

[GrampyJim]

If the pump is running constantly, forget the lines to the hubs. If we understand the system, we will realize that vacuum is sent to the hubs for only very short periods of time... not enough to make the pump run continuously.

The first step is to check the pump itself.... disconnect the vac line going to the reservoir and substitute a gauge. Vacuum should build quickly to about 15 inches and the pump should shut off. If = no, the pump is faulty.... If = yes, use a logical progression for diagnosis of the remainder of the system.

Heavy on the "logical".

 

[kc_maverick]

This has been an informative thread (for me). I didn't understand how the PVH worked. A couple of weeks ago, when I switched to 4x4 my A/C went to defrost. After about 45 seconds it returned to normal. From what I am reading above this means a problem between the PVH solenoid and the hubs (or the hubs themselves) correct? If it helps, the truck did not "feel" as if it shifted into 4-wheel drive, though the indicator light was illuminated.