is it possible the 4WD is engaging on its own?

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pennyanguy

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Hi all, 2007 Expo EL LTD with 101,000 miles... bought it last year and it is CHERRY, never towed. today, as driving about 45 MPH...felt an incident... almost like I ran over a piece of metal... turned around to see if I had and no metal in the road. 0 miles down the road it happened again, just barely... then a third time...it seemed to me the ABS had engaged for a split second. Roads barely damp...has been raining but not hard and I was not braking so that didnt make sense to me.

Then, another few miles down the road...something drastic happened... felt and sounded like gears engaging while travelling at 45...lasted maybe 1/2 second...I broke hard, pulled to the side, then all felt OK. Definite ratcheting sound, and sounded to me like it was coming from the drivers front wheel. drove home another 5 miles slow with no additional noise...but something is definately going on.

Any help here? I am concerned something will explode if I drive at speed and the 4WD engages...
 

JExpedition07

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Hi all, 2007 Expo EL LTD with 101,000 miles... bought it last year and it is CHERRY, never towed. today, as driving about 45 MPH...felt an incident... almost like I ran over a piece of metal... turned around to see if I had and no metal in the road. 0 miles down the road it happened again, just barely... then a third time...it seemed to me the ABS had engaged for a split second. Roads barely damp...has been raining but not hard and I was not braking so that didnt make sense to me.

Then, another few miles down the road...something drastic happened... felt and sounded like gears engaging while travelling at 45...lasted maybe 1/2 second...I broke hard, pulled to the side, then all felt OK. Definite ratcheting sound, and sounded to me like it was coming from the drivers front wheel. drove home another 5 miles slow with no additional noise...but something is definately going on.

Any help here? I am concerned something will explode if I drive at speed and the 4WD engages...

You have a failed or failing Vacuum Hub Actuator. I’d recommend replacing both side IWE’s (hub actuators) and the solonoid. Nothing will explode, it’s the hubs partially engaging to the front driveshaft because they are losing vacuum, the T-Case is not engaging. My truck exhibited the same symptoms, please view the attached:

 
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pennyanguy

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THANK YOU!!!! sounds just like what I felt happen! any idea where that solenoid is on the 2007 expedition?
 

JExpedition07

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THANK YOU!!!! sounds just like what I felt happen! any idea where that solenoid is on the 2007 expedition?

Yes, when you open the hood it is toward the front of the vehicle attached to the left side of the fan shroud. It has plastic cap that reads MADE IN USA on the top.
 
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pennyanguy

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OK guys, I need more help here.

I found the solenoid, replaced it...and could swear the incident happened at least twice again...its so fast its hard to tell but my 14 year old son thinks he felt it too.... sooo , make an appointment at a very good local shop... they go over the whole system...check vacuum, codes, blah blah blah...nothing. Tech. takes me for a ride , says he knows of the "symptom" well and he can usually reproduce it by hard liftoff after acceleration...nothing...Puts it on the lift, those vacuum hub actuators look perfect...as does everything else under there...really this truck is so clean its a marvel...especially for this area...it looks better underneath then my friends 1 year old Ram! He looks at me and says "I cant fix whats not broke" Cant blame him...I drive away tentatively

let me interject here this is not my "everyday" vehicle...I work from home and drive maybe 30-40 miles a week...sometimes...I just do not use the truck enough to say i have lots of time on it. I just do not drive enough to put enough miles on it to see an intermittent problem.

So, in the past 3 weeks I have driven around, probably less that 100 miles but thats all I got, staying "close to home"...trying to be uber-vigilant to any noise... this is not a comfortable way to use my truck. I just can not get comfortable driving it...

I am thinking I may be barking up the wrong tree... the noise I hear, when I hear it, is not the gear on gear I hear on these utube vids... I am a Marine Mechanic by trade...this does not sound like clicking...like a lower unit sliding into gear. mostly...it sounds like I just ran over a piece of dripcap... a tinny aluminum bouncing noise, happens once in maybe 50-75 miles...then all is cool again. What really rattled me was the one time something violent happened...that was definitely gears slamming together at 45 MPH...one time... I have not heard anything else like it or been able to replicate it at all since.

So, looking for some other ideas here. one question I keep asking myself is , can I run in 4A (AWD) mostly? That would , should, eliminate this screwy vacuum hub system right?.. How fast can you drive in 4A? book does not say other that dont shift into 4A above 55, can I drive 60-65 in it?

Another Q I keep rattling with is what could happen? the system is meant to shift into and out of 4WD while underway...so if it does on its own (VHA fail) ...all SHOULD be ok...at least nothing should break.

Any help here would be great!
 

1955moose

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You can't run in 4wd high or low on dry pavement for any length. It will destroy your transfer case and all Involved up front. Sounds like you need another shop to diagnose your noise. Next time you hear it, have your phone handy, and try recording it. The Iwe wheel actuators do fail, along with the vacuum lines going to them. Can you pinpoint what side you hear noise. You or a shop may also want to check fluids in both front differential, and transfer case. Intermittent noises are toughest to diagnose. I'm sure with time and miles, your noise will become more frequent, and louder, they always do.

Sent from my N9131 using Tapatalk
 
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pennyanguy

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Moose,

Thanks for the input. I know I cant run in 4WD on dry pavement...but the book at least says you can run in 4A (advance trac)...not sure how "correct" that is though....does it mean for short duration or ok for a 20-30 mile run?
 

JExpedition07

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Does it occur when accelerating? That would indicate a bad vacuum hub check valve assembly. Replaced mine with both actuators and solonoid:

02A23AB9-BA68-4BD7-8882-40998DACEE88.jpeg
 
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pennyanguy

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OK, I will get one of those too...One Q whats the part #? the one on the bag 8L1Z-3A788-A shows to be a vacuum hose
 

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