4 wheel drive system question

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Jul 29, 2004 | 07:56 PM

#16

Hoss350

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From: Tustin,(orange county) Ca.

Quote:

Originally Posted by Big Orn

How long between the time he shutoff the engine, refired it, then got stuck?

He could have a leak either in the hubs or anywhere along the system.

If there's not a leak in the system, the hubs should remain locked for quite awhile. Of course, the longer it sits, the more time the vac system has to bleed off, but I would think it would have to be hours.

it's over night, so theres alot of time for the vac. system to bleed out, if that's the case, we basically get to glamis, turn park, and next morning his hubs were disengaged.

Jul 30, 2004 | 09:13 AM

#17

warmdye

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Joined: Apr 2002

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From: Paducah KY

I thought it was decided it took a pulse of vacuum to unlock the hubs? I had suggested the hubs where under constant vacuum the entire time they are locked previously and was shot down. I'm confused.

Jul 30, 2004 | 09:58 AM

#18

RED-STROKE

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I tested my system with a vacuum guage...It pulses 15 in hg for about 15 seconds to lock the hubs in, and then it pulses 7 in hg for 5 seconds when the hubs dissengage.

Jul 30, 2004 | 01:38 PM

#19

BigRyanKP

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Joined: Oct 2003

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From: New Hampshire

Just thought I would chip in here.. Last winter in a snow storm I had was driving around with the hubs unlocked but vacuum accentuated, they worked fine all the way to work and then I drove through a snow bank and parked on it, leaving my truck in 4x4. When it came time to leave work I went to pull out of the snow bank and there was no power getting to my front wheels and there should be since I left it in 4wd, and since for some reason the hubs on my truck require a wrench to turn because they are so stiff I was not able to get it in 4wd. I ended up rocking the truck back and forth to get it unstuck and then trying to drive home uphill in a snowstorm without 4wd was an adventure. Anyways the next day I looked under my truck and saw that I must had broken the passengers side vacuum line when I blew through the snow bank, so I reconnected it and the 4wd worked fine after that.

Jul 30, 2004 | 02:45 PM

#20

RED-STROKE

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The hubs do not require vacuum to stay engaged. I pulled mine apart today and discovered that they work kind of like a ball point pen...click on...click off. Any vacuum pulse over 10 in hg will engage them. Any vacuum pulse at about 7 in hg will unlock the hubs. There are two solenoid valves that are built into one unit. One delivers the large pulse, and one delivers the smaller dissengage pulse. After the hubs initially lock in there isn't any more vacuum applied to them until you dissengage 4 wheel. I teed a vacuum guage into the line so that I could monitor what it was doing. Seems like an over-engineered design to me.

Jul 30, 2004 | 03:07 PM

#21

iskybantilus

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Joined: Feb 2003

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From: NJ ... the garbage state

over engineering ... definatly. Mine always do what i want them to. I get out, lock them, and they stay locked. I get out, unlock them, and they stay unlocked. Only vaccum required is to clean the truck out after fun

....

hehe

i'll be here all week

Aug 2, 2004 | 10:00 AM

#22

Big Orn

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Joined: Jun 2003

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From: NE Texas

Quote:

Originally Posted by warmdye

I thought it was decided it took a pulse of vacuum to unlock the hubs? I had suggested the hubs where under constant vacuum the entire time they are locked previously and was shot down. I'm confused.

I was referring to a leak not allowing it to engage properly. I don't fully understand the complete makeup of the system, but I do know that a vac leak can give you the blues - maybe even make it "appear" to engage allowing the axles to turn, but can unlock by force in some instances under load.
Here is a better, but still not complete, explanation:
https://www.ford-trucks.com/forums/s...highlight=pvh+

It's the entry at the bottom of the page.

Aug 2, 2004 | 10:20 AM

#23

michaelmueller

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Joined: Mar 2004

Posts: 127

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From: bay city mi

what I want to know is how vacuume actually get to the lock out assembly, if you remove your lock outs and look inside the hub, you will notice no visable vacuume ports.