How JustAnswer Works:

  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.

Ask AlvinC Your Own Question

AlvinC
AlvinC, Ford Technician
Category: Ford
Satisfied Customers: 1241
Experience:  With Ford 20+years as Dealership Technician Ford Senior Master Technician Gas and Diesel
10384837
Type Your Ford Question Here...
AlvinC is online now
A new question is answered every 9 seconds

2006 Ford F-350 Dual rear wheel.4 wheel drive engages but front

Customer Question

2006 Ford F-350 Dual rear wheel.4 wheel drive engages but front end don't engage. I unpluged the vacuum lines (1at the time) from the front hubs with the 4X4 switch engaged. I could not feel any vacuum at the end of the hose. A/C seems to be working fine. Manually locking hubs the 4X4 works. I can't seem to find any kinks in vacuum lines. Any sugestions as to what the problem could be?
Submitted: 6 years ago.
Category: Ford
Expert:  AlvinC replied 6 years ago.
CustomerWhat engine do have?, Al

 

Customer: replied 6 years ago.
The engine is 6.0 power stroke
Expert:  AlvinC replied 6 years ago.
Customer Does you heater a/c blower blow on defrost only?
Customer: replied 6 years ago.
no it works fine
Expert:  AlvinC replied 6 years ago.
Customer The vacuum pump is common for failing, but when it does your blower will default to defrost since it is working properly you must have a vacuum leak at or to the hubs. You will need a vacuum gauge to check the sytem. This a vacuum pulse lock system. Here is a description of it's operation. If you can get a vacuum gauge and let me know and we will find your cause, Al

 

Pulse Vacuum Hublocks

The electronic shift-on-the-fly (ESOF) system has a feature which allows the driver to override the vacuum-operated hublocks. When the front hublock dials are manually turned to the LOCK position, the hublocks are locked through the dial at all times, regardless of the position of the instrument panel mode select switch (MSS).

When the front hublock dials are manually turned to the AUTO position, the hublocks use an internal spring-locking mechanism that is vacuum-operated by the ESOF system, and are locked with the MSS in the 4H or 4L position and unlocked with the MSS in 2H position. Refer to Hublock in this section for additional AUTO hublock system operation.

Hublock Operation

With the hublocks in the AUTO position, the 4X4 ESOF system uses timed vacuum sequences to lock and unlock the wheel ends when switching the instrument panel MSS between 2WD and 4X4 modes. A high vacuum level (222 mm [8.75 in] Hg and greater) is applied to the hublocks to lock the internal spring mechanism that engages (locks) the hublocks for 4X4 mode, and a lower vacuum level (114 to 184 mm [5.9 to 7.1 in] Hg) is applied to unlock the spring mechanism that disengages (unlocks) the hublocks for 2WD mode. The vacuum signals are supplied to the hublocks by system components, including the 4X4 control module, wiring harness, solenoid, vacuum harness and vacuum seals. As a first step in service, eliminate obvious items such as loose wiring connections, loose vacuum connections or damaged vacuum lines.

Hublock Engagement/Disengagement Time

With the hublock dials in the AUTO position, switching the instrument panel MSS to 4X4 HIGH or 4X4 LOW results in the high vacuum level being applied to the hublocks, which lasts for at least 51 seconds (including a venting cycle). The hublocks should engage during this time through the spring mechanism. Switching the MSS to 4x2 less than 51 seconds after the MSS has been switched to 4X4 HIGH or 4X4 LOW will not interrupt the high vacuum level; instead, the lower vacuum level will be applied after the high vacuum level cycle is completed.

With the hublock dials in the AUTO position, switching the MSS to 2WD results in the lower vacuum level being applied to the hublocks, which lasts for about 15 seconds. However, the actual time required for the hublocks to disengage by spring force can vary considerably due to the effects of driveline wind-up. Road bumps, vehicle speed, acceleration cycles or momentary reversal of direction can assist this process. Switching the MSS to 4X4 HIGH or 4X4 LOW always overrides the lower vacuum level cycle and results in an immediate high vacuum level and in locking of the hublocks.

Manual Override

The AUTO hublocks have a manual override selector dial, which, when turned to the LOCK position, will keep the hublocks locked (through the dial) at all times, regardless of the position of the instrument panel MSS. (Always set both hublock dials to the same position.) If the hublock dials are manually turned from the AUTO to the LOCK position, and the high vacuum level is applied to the hublocks (by switching the MSS from 2WD to 4X4 HIGH or 4X4 LOW), the hublocks will be locked through the dial as well as through the internal spring mechanism. In this case, turning the hublock dials back to the AUTO position will leave the hublocks in (spring) locked mode until the lower vacuum level is applied to the hublocks (by switching the MSS from 4X4 or 4X4 LOW to the 4x2). (This is not an issue if the hublock dials have been in the AUTO position and the MSS has been switched from 4X4 HIGH or 4X4 LOW to 2WD at least once.) Alternatively, the hublock mechanism can be reset to free mode at any time by turning the hublock dial from AUTO to LOCK to AUTO at least 2 times.

Customer: replied 6 years ago.
Thanks, XXXXX XXXXX get a vacuum gauge and check the vacuum at the hubs. How do I get back intuch with you?
Expert:  AlvinC replied 6 years ago.
Customer Just come back to JA your question will stay open for 24 hours, and if I don't hear from you in that time I will reply to you. Thanks, Al
Customer: replied 6 years ago.
Okay thans agian.
Customer: replied 6 years ago.

Hello AlvinC;

 

I checked the vacuum at the hubs, there is no movement in the gauge. Now while checking it the A/C went to defrost only then went back to working normaly, servral times. I also checked the fuses, no problem there.

Expert:  AlvinC replied 6 years ago.
Customer Make sure the engine is running when you check vacuum at the hubs. If you are loosing vacuum to the a/c and it goes to defrost you probably have a bad vacuum pump. Here is The TSB for the vacuum pump and installation instruction, Al

Click here for TSB

 

Click here for instructions

AlvinC, Ford Technician
Category: Ford
Satisfied Customers: 1241
Experience: With Ford 20+years as Dealership Technician Ford Senior Master Technician Gas and Diesel
AlvinC and 8 other Ford Specialists are ready to help you
Customer: replied 6 years ago.

Hi AlvinC;

Just got in from work. Thanks for your help and for the instructions, I beleve this should fix the problem. Thanks Again.

Expert:  AlvinC replied 6 years ago.
Customer Glad to help. If this is not your issue let me know, Al
Customer: replied 6 years ago.

Hello AlvinC;

The vacuum pump is running till what seems to be a cut off switch cuts it off. (I unhooked and rehooked it several times) The vacuum canaseter seems to mantain vacuum for a long time so I don't think there is a leak. With the engine off you can turn the switch on the dash and here what sounds like the hubs lock in. But thay don't. I gess I'll take it to the Ford dealer Tuesday. Thank You,Customer

JustAnswer in the News:

 
 
 
Ask-a-doc Web sites: If you've got a quick question, you can try to get an answer from sites that say they have various specialists on hand to give quick answers... Justanswer.com.
JustAnswer.com...has seen a spike since October in legal questions from readers about layoffs, unemployment and severance.
Web sites like justanswer.com/legal
...leave nothing to chance.
Traffic on JustAnswer rose 14 percent...and had nearly 400,000 page views in 30 days...inquiries related to stress, high blood pressure, drinking and heart pain jumped 33 percent.
Tory Johnson, GMA Workplace Contributor, discusses work-from-home jobs, such as JustAnswer in which verified Experts answer people’s questions.
I will tell you that...the things you have to go through to be an Expert are quite rigorous.
 
 
 

What Customers are Saying:

 
 
 
  • AlvinC answered a question about my Ford truck that only someone with an in-depth knowledge of his subject would have known what was going on. Rich D USA
< Last | Next >
  • AlvinC answered a question about my Ford truck that only someone with an in-depth knowledge of his subject would have known what was going on. Rich D USA
  • Because of your expertise, you armed me with enough ammunition to win the battle with the dealer. They are installing a fuel filter and fuel pump at no charge to me. Molly USA
  • I needed help with my car on Saturday morning....got a response in 5 minutes, and it was the perfect solution. Thanks again to your service. Jason V. Kirkland, WA
  • I do know, after going though this with JustAnswer, that I can somewhat trust my mechanic but I will always contact you prior to going there. BR New Jersey
  • I would (and have) recommend your site to others I was quite satisfied with the quality of the information received, the professional with whom I interacted, and the quick response time. Thanks, and be sure that I'll be back whenever I need a question answered in a hurry. Stephanie P Elm City, NC
  • used your service this weekend with "Trecers" help. thank you ,thank you, thank you. replaced an A/C fan motor. Local Auto Zone had part. $15.00 "tracer" fee and $40.00 for parts, I saved several hundreds of dollers at a shop. i will recommend you and use you in the future. David L. Richmond, TX
  • 9 dollars, 2 hours of my time, and I drove away. Your diagnosis was right on the mark. Thank you so much. Phil Marysville, CA
 
 
 

Meet The Experts:

 
 
 
  • Ron

    ASE Certified Technician

    Satisfied Customers:

    20942
    23 years with Ford specializing in drivability and electrical and AC. Ford certs and ASE Certs
< Last | Next >
  • http://ww2.justanswer.com/uploads/FO/fordguy4u/2011-12-17_222940_HPIM1257.64x64.JPG Ron's Avatar

    Ron

    ASE Certified Technician

    Satisfied Customers:

    20942
    23 years with Ford specializing in drivability and electrical and AC. Ford certs and ASE Certs
  • http://ww2.justanswer.com/uploads/MU/muddyford/2012-6-13_1204_1.64x64.png Chris (aka- Moose)'s Avatar

    Chris (aka- Moose)

    Ford Technician

    Satisfied Customers:

    22382
    16 years experience with Ford.
  • http://ww2.justanswer.com/uploads/JM/jmcdo28/2012-2-23_01655_resized.64x64.jpg John Mc's Avatar

    John Mc

    Ford Technician

    Satisfied Customers:

    5493
    19 years Ford Lincoln Mercury experience
  • http://ww2.justanswer.com/uploads/wmarti7/2009-4-18_04332_Avatar.jpg Chuck's Avatar

    Chuck

    ASE Certified Technician

    Satisfied Customers:

    1684
    33 Years Experience,Ford Senior Master,ASE Master,L1 Advanced Engine Performance
  • http://ww2.justanswer.com/uploads/CR/crzydrvr00/2013-11-3_12123_246347.64x64.jpg Richard's Avatar

    Richard

    ASE Certified Technician

    Satisfied Customers:

    1518
    12 years at a Ford Lincoln/Mercury and Jaguar dealer as a technician and shop foreman.
  • http://ww2.justanswer.com/uploads/BA/baddad1/2014-4-1_23659_avatar.64x64.jpg Mike V.'s Avatar

    Mike V.

    Auto Service Technician

    Satisfied Customers:

    789
    25 years experience on all makes and models, Licensed NYS Inspector.
  • http://ww2.justanswer.com/uploads/lostrider/2009-9-26_23144_php4VNWAA_c1PM1.jpg lostrider's Avatar

    lostrider

    Ford Technician

    Satisfied Customers:

    2940
    ASE Master Technician, Ford Senior Master Technician,Diesel certified, ASE Master, 22 yrs FORD exp.
 
 
 

Related Ford Questions

Chat Now With A Ford Mechanic
AlvinC
AlvinC
Ford Mechanic
1241 Satisfied Customers
With Ford 20+years as Dealership Technician Ford Senior Master Technician Gas and Diesel