2wd Low obd2
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Cargo Master
Joined: Apr 2003
Posts: 2,058
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From: Too close to Houston
That thread is very informative and deals with installing a relay to keep the vacuum solenoid actuating to activate the automatic hubs.
I wonder if it wouldn’t be easier to add a solenoid to interrupt the vacuum signal to one (or both) hubs. Unlocking one would disable the front axle with the stock open differential. Something like this normally closed valve hooked to a key-on upfitter should do. The hub would be active with the upfitter on and vented with the upfitter off. The plus for me would be that it doesn’t involve cutting and splicing any OEM wiring. Vacuum hoses are cheap and easy to replace/modify.
Universal Air Conditioner SW 9001C A/C Solenoid Valve
I wonder if it wouldn’t be easier to add a solenoid to interrupt the vacuum signal to one (or both) hubs. Unlocking one would disable the front axle with the stock open differential. Something like this normally closed valve hooked to a key-on upfitter should do. The hub would be active with the upfitter on and vented with the upfitter off. The plus for me would be that it doesn’t involve cutting and splicing any OEM wiring. Vacuum hoses are cheap and easy to replace/modify.
Universal Air Conditioner SW 9001C A/C Solenoid Valve
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That thread is very informative and deals with installing a relay to keep the vacuum solenoid actuating to activate the automatic hubs.
I wonder if it wouldn’t be easier to add a solenoid to interrupt the vacuum signal to one (or both) hubs. Unlocking one would disable the front axle with the stock open differential. Something like this normally closed valve hooked to a key-on upfitter should do. The hub would be active with the upfitter on and vented with the upfitter off. The plus for me would be that it doesn’t involve cutting and splicing any OEM wiring. Vacuum hoses are cheap and easy to replace/modify.
Universal Air Conditioner SW 9001C A/C Solenoid Valve https://www.amazon.com/dp/B003R43J2C..._dRxxDb9DSMTSR
I wonder if it wouldn’t be easier to add a solenoid to interrupt the vacuum signal to one (or both) hubs. Unlocking one would disable the front axle with the stock open differential. Something like this normally closed valve hooked to a key-on upfitter should do. The hub would be active with the upfitter on and vented with the upfitter off. The plus for me would be that it doesn’t involve cutting and splicing any OEM wiring. Vacuum hoses are cheap and easy to replace/modify.
Universal Air Conditioner SW 9001C A/C Solenoid Valve https://www.amazon.com/dp/B003R43J2C..._dRxxDb9DSMTSR
Senior User
Joined: May 2006
Posts: 221
Likes: 2
That thread is very informative and deals with installing a relay to keep the vacuum solenoid actuating to activate the automatic hubs.
I wonder if it wouldn’t be easier to add a solenoid to interrupt the vacuum signal to one (or both) hubs. Unlocking one would disable the front axle with the stock open differential. Something like this normally closed valve hooked to a key-on upfitter should do. The hub would be active with the upfitter on and vented with the upfitter off. The plus for me would be that it doesn’t involve cutting and splicing any OEM wiring. Vacuum hoses are cheap and easy to replace/modify.
Universal Air Conditioner SW 9001C A/C Solenoid Valve https://www.amazon.com/dp/B003R43J2C..._dRxxDb9DSMTSR
I wonder if it wouldn’t be easier to add a solenoid to interrupt the vacuum signal to one (or both) hubs. Unlocking one would disable the front axle with the stock open differential. Something like this normally closed valve hooked to a key-on upfitter should do. The hub would be active with the upfitter on and vented with the upfitter off. The plus for me would be that it doesn’t involve cutting and splicing any OEM wiring. Vacuum hoses are cheap and easy to replace/modify.
Universal Air Conditioner SW 9001C A/C Solenoid Valve https://www.amazon.com/dp/B003R43J2C..._dRxxDb9DSMTSR
Last edited by RPFB; Aug 21, 2019 at 03:22 PM. Reason: oops!
Cargo Master
Joined: Apr 2003
Posts: 2,058
Likes: 424
From: Too close to Houston
Right. Wonder if it would work and would throw any codes. I don’t think there’s any kind of feedback from the hub to report it actually locked, but don’t know that for sure.
Cargo Master
Joined: Apr 2003
Posts: 2,058
Likes: 424
From: Too close to Houston
I thought vacuum locked the hubs. At least I think I’ve seen reports of the hubs not locking automatically after the vacuum hose was inadvertently disconnected during lift kit installs and such.
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From the WSM:
Constant Vacuum Hublock (CVH) System
The ESOF system engages the front driveline to the front wheels via the CVH system. The Constant Vacuum Hublocks (CVHs) have 2 modes: AUTO and LOCK. Always set both CVH dials to the same position. When in the AUTO mode, the CVHs are disengaged (no vacuum) in 2H (4X2), engaged in 4H (4X4 high) and 4L (4X4 low), and automatically operate upon 4WD mode shifts. During a 4WD mode shift, the TCCM commands the CVH system vacuum solenoid to supply or remove vacuum to the CVHs which engages or disengages the front wheels to or from the front driveline. When in LOCK mode, the CVHs are engaged at all times and the vacuum system has no effect on the operation of the CVHs (refer to Manual Override in this section for more information regarding the LOCK position). AUTO mode should be used for system operation convenience and increased fuel economy. A minimum vacuum level of 6 inches of Hg is required to correctly operate the CVH system. The vacuum signals are supplied to the CVHs by system components, including the TCCM , wiring harness, solenoid, vacuum harness and vacuum seals. On diesel engine vehicles, vacuum is supplied by a gear-driven pump that is mounted to the front of the engine behind the accessory drive cooling fan driver and is serviced as an assembly. For additional information, refer to Section 206-07. As a first step in service, eliminate obvious items such as loose wiring connections, loose vacuum connections or damaged vacuum lines.
Manual Override
The CVHs have a manual override selector dial, which, when turned to the LOCK position, keeps the CVHs locked (via 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 CVH dials are manually turned from the AUTO to the LOCK position, and vacuum is supplied to the CVHs (by switching the MSS from 2H (4X2) to 4H (4X4 high) or 4L (4X4 low), the CVHs are locked through the dial as well as through the internal spring mechanism. In this case, turning the CVH dials back to the AUTO position leaves the CVHs in (spring) locked mode until vacuum is removed from the CVHs (by switching the MSS from 4H or 4L to 2H). (This is not an issue if the CVH dials have been in the AUTO position and the MSS has been switched from 4H or 4L to 2H at least once.) The CVH should be left in the AUTO position for increased fuel economy.
The ESOF system engages the front driveline to the front wheels via the CVH system. The Constant Vacuum Hublocks (CVHs) have 2 modes: AUTO and LOCK. Always set both CVH dials to the same position. When in the AUTO mode, the CVHs are disengaged (no vacuum) in 2H (4X2), engaged in 4H (4X4 high) and 4L (4X4 low), and automatically operate upon 4WD mode shifts. During a 4WD mode shift, the TCCM commands the CVH system vacuum solenoid to supply or remove vacuum to the CVHs which engages or disengages the front wheels to or from the front driveline. When in LOCK mode, the CVHs are engaged at all times and the vacuum system has no effect on the operation of the CVHs (refer to Manual Override in this section for more information regarding the LOCK position). AUTO mode should be used for system operation convenience and increased fuel economy. A minimum vacuum level of 6 inches of Hg is required to correctly operate the CVH system. The vacuum signals are supplied to the CVHs by system components, including the TCCM , wiring harness, solenoid, vacuum harness and vacuum seals. On diesel engine vehicles, vacuum is supplied by a gear-driven pump that is mounted to the front of the engine behind the accessory drive cooling fan driver and is serviced as an assembly. For additional information, refer to Section 206-07. As a first step in service, eliminate obvious items such as loose wiring connections, loose vacuum connections or damaged vacuum lines.
Manual Override
The CVHs have a manual override selector dial, which, when turned to the LOCK position, keeps the CVHs locked (via 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 CVH dials are manually turned from the AUTO to the LOCK position, and vacuum is supplied to the CVHs (by switching the MSS from 2H (4X2) to 4H (4X4 high) or 4L (4X4 low), the CVHs are locked through the dial as well as through the internal spring mechanism. In this case, turning the CVH dials back to the AUTO position leaves the CVHs in (spring) locked mode until vacuum is removed from the CVHs (by switching the MSS from 4H or 4L to 2H). (This is not an issue if the CVH dials have been in the AUTO position and the MSS has been switched from 4H or 4L to 2H at least once.) The CVH should be left in the AUTO position for increased fuel economy.
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