As some of you may know I am having problems with my auto-locking hubs disengaging on my 02 F-250 CC V10. They engage fine for some reason though. I now feel I may have a vacuum leak. I have done the turn the A/C to max cool trick and it switched to vent after I turned the ESOF system off, but not when turn on. Does it take more vacuum to disengage than engage?

I am going the replace the vacuum lines in the wheel wells and see what that does.

My big question is this. I noticed the the plastic ring on one of the knuckle seals has broken loose and the other is not far behind. The seal looks like it is still intact; just the ring is loose. Will these seal cause a vacuum leak?

Thanks Guys,
Jason

 

The vacuum pulse to release the hubs is lower than the pulse to engage. The ring, under pressure, may cause it to lose vacuum momentarily.

 

I know that the manual gives a spec, but IIRC it's around 10" to lock and 6" to unlock.

EDIT: Looking at my shop manual gives me this information:

When going to 4x4 (locking the hubs): a vacuum of 10" or higher is maintained for 45 seconds.

When going to 2wd (unlocking the hubs): a vacuum of 5.8" - 7.3" is maintained for 15 seconds.

It also talks about a vacuum test on the hub itself. Use a vacuum pump and pump the vacuum up to 20". If it drops more than .5" (goes less than 19.5") in 30 seconds, then there's a problem.

I hope this helps.

 

In your situation, it sounds like the vacuum solenoid is bad. It's responsible for metering the vacuum pulse, and it sounds like it's low-side is leaking.

If you check the vacuum hoses going to the vacuum solenoid, you will see one coming from the vacuum reservoir to the solenoid, and one from the solenoid going to the front hubs. Where the hose from the solenoid goes to the hubs, there will be a "T" in it and it branches off to both hubs. Disconnect the vacuum hose at the "T" and put a vacuum gauge on it, and watch the vacuum as you turn the ESOF switch from 4x2 to 4x4, wait 20 seconds, and go back to 4x2 (with the engine running of course).

If you see no vacuum pulse going from 4x4 to 4x2, or not enough (I think 6" is right), the vacuum solenoid is shot.

 

I found this somewhere on this, or another, web site. I believe that it is a way to test the vacuum system up to, but not including, the hubs themselves. You may find it helpful. However, if you are getting them to work one way but not the other it may be the solenoid. Or, it is a leak limiting the amount of vacuum. Thereby only allowing the lower switchover to work.

Anyway, here it is.....

Hublock Vacuum System Leak Test

NOTE: This procedure requires the use of a calibrated vacuum gauge that is accurate to within a minimum of 0.1 in-Hg. It is recommended the Pressure Vacuum Module 105-R0099 or equivalent be used.

Make sure hublocks are in the AUTO position.
Lift and support the vehicle off the ground until the front tires can be spun freely. Refer to Section 100-02
NOTE: The engine is required to be at idle during the following steps to supply the vacuum required for the hublocks to engage and disengage.
Start the engine and allow to idle.
Turn the mode select switch (MSS) to the 2WD position and wait 15 seconds. If switching from 4X4 mode, wait an additional 45 seconds.
Disconnect the vacuum line at the right front knuckle and install a vacuum gauge on the line.
Disconnect the vacuum line at the left front knuckle and plug the line.
NOTE: Normal operation applies engagement vacuum for 45 seconds and then drops to 0 in-Hg.
Turn the MSS to 4X4 and observe the vacuum reading. The vacuum reading should remain at or above 10 in-Hg for 45 seconds.
NOTE: Normal operation applies regulated disengagement vacuum for 15 seconds and then drops to 0 in-Hg.
Turn the MSS to 2WD and observe the vacuum reading. The vacuum reading should remain between 5.8 and 7.3 in-Hg for 15 seconds.
Remove the vacuum gauge and connect the vacuum line at the right front knuckle. Turn the MSS to 4X4.
NOTE: The right front axle shaft and universal joint should turn.
Wait one minute then rotate the right front tire one revolution forward and one revolution backward while observing the right front axle shaft and universal joint. Turn the MSS to 2WD.
NOTE: The right front axle shaft and universal joint should not turn.
Wait one minute then rotate the right front tire one revolution forward and one revolution backward while observing the right front axle shaft and universal joint.
Install the vacuum pump and gauge line on the knuckle and pump to 20 in-Hg. If the vacuum drop is not equal to 0.5 in-Hg in 30 seconds, Go To Pinpoint Test G for further diagnosis of the hublock system.
Repeat steps 1 through 13 for the LH hublock. If results are not as indicated, Go To Pinpoint Test G for further diagnosis of the hublock system.

 

Thanks guys. I will try these tips out this weekend if the weather is nice.

 

This is straight out of the Ford shop manual.

 

Looks like krewat is going to be right on with the silenoid. I hooked my a vacuum gauge to the output and only got about 4 to 5 in. on engage and nothing on disengage. Even that 4 to 5 in was very intermitten.

Thanks guys.