2nd Gen Non-Engine/Transmission 4WD will not fully disengage

[PDDailey]

Have a 1999 3/4 ton CTD with 5spd manual and 4wd with the lever on the floor,,,,,used 4High the other day and when I shifted out of 4H to 2H 4wd lite stayed on... . I turned sharp circles and it did not feel like 4wd was engaged, but I cannot turn the front driveshaft by hand when in 2H with wheels straight or turned..... I did notice a while back some 'noises" coming from what seemed the drivers side hub when in 2H that disappeareed when in 4H, then returned when back to 2H,,,looked underneath and see no bad vaccumm hoses/lines evident... . any down and dirty way to determine if my hub hubs are hanging up versus the vacuum motor not doing its job?



TIA

 

[MLee]

check the vacuum tubes. make sure they are all connected tught.

 

[DWeaver]

I might be wrong on this for a '99.

The light is run off the switch that is on the axle next to the vacuum chamber that runs the CAD. The CAD is just a fork that moves a collar on the axle spline of the passenger side that locks and unlocks the pass. axle.

I would check the wiring to the switch. If that looks good, unbolt the CAD housing and make sure the fork and collar are sliding correctly.

 

[Road Dog]

DWeaver is right -- the 4WD switch is on the CAD and would indicate that the fork is not moving correctly. It could be the vacuum actuator on the CAD or the vacuum lines (mine touched the exhaust and melted on my '98) or the vacuum switch in the transfer case. My money's on the lines. One is cracked or melted.

 

[mwilson]

I vote for the transfer case switch.



If there is no vacuum present due to a leak the switch plunger will push the collar over to 2wd.



If it is staying in 4wd and the light is on there is vacuum.



The only exception that comes to mind would be a twisted spline on either the intermediate shaft or axle stub shaft, that would hold the collar over both spines.



Mike.

 

[HHhuntitall]

Having seen similar issues, it could also be the vacuum vent stopped up. Or a line. I've had several that won't move very easily one way or the other, and it's ended up being the vent on the back of the engine that was stopped up. It runs from one port on the vacuum switch up to the back of the engine, and has a dust cover and vent on it. On the older 12v trucks, I think it was a light green color line for the vent tube. It won't let air into the vacuum motor on the back side of the diaphram, so it can't move towards the vacuum. THEN, when it does finally move, it takes forever for it to move back... ... and sometimes the plastic lines get stopped up from dust, water, oil, etc, and that won't let the air through... ... . it's a PITA to replace all the switches and vacuum motor and it still won't move!!!#@$%! I think you can tell how I know.....