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Posted on Jan 02, 2017
sounds like it is loosing vacuum check all the lines for a crack even the engine lines will cause it to loose vacc. pressure. if it is not run to the vacuum reserve canister you may not have enough vacc. to hold the actuator in several times I just run new lines and that helped and not very costly.
Posted on Dec 25, 2008
check all wire conections also replace the actuator on the front axle but check for power there first if you have power replace that switch as well .
Posted on Aug 27, 2009
Having the same exact problem but with my 1999 escalade. Thought it was the actuator bought a new one installed it transfer case would engage but front end wouldnt lock. Took it out of housing left it plugged in got a friend to go through all the 4wd for me and the plunger never moved out the actuator. Checked my wiring harness which is a four prong ann it had one hot prong like it is suppose to. Traced wires even replaced dash switch same problem. Taking it to local dealership tom to have it checked for codes. I was told it could be the transfercase actuator even though its workin that actuator is what sends power to the front to engage the actuator to lock the differential.
Posted on Sep 16, 2009
On the full size, the front actuator is electric, not vacuum.
When in 4wd mode, a switch on top of the transfer case conducts 12 volts out to the actuator. Wire #50 (brown) is the 12v feed, and it conducts to the light blue wire (#900) to the actuator.
When shifted out of 4wd, the switch opens up and no voltage goes to the actuator.
Check voltage at the connector for the front actuator (at the front differential - it looks like a large bullet that threads into the front diff.) If it has 12 volts, the actuator is the problem. If it does not have 12 volts, check the transfer case switch and the power feed to the transfer case.
I'll assume it is the actuator, if the plug to the actuator is getting 12 volts when in 4wd.
The way this actuator works, is it is a sealed chamber that gets heated by voltage. When it heats, the pin in the end swells and pushes a shift fork in the front differential. The shift fork engages a spline on the passenger side of the differential, and boom! you have 4WD.
GM offered an upgrade to this actuator that is a motor instead of a heated device. However, it requires a small harness addition, a spacer, and a new actuator. It is about a $150 to $200 option.
Good luck. The actuator is usually the problem 90% of time but recheck all of the wire harness just to maker sure there is no short before replacing any parts.
88-UP C/K ACTUATOR UPGRADE
VEHICLE SERVICED: 1994 CHEVROLET FULL SIZE
PURPOSE: IMPROVE AXLE CONNECT ENGAGEMENT TIME AND
SYMPTOMS: NO FRONT DRIVE AXLE ENGAGEMENT WHEN SHIFTED
Obtain the following GM part numbers:
(1) 26060073 Actuator
(1) 88959465 Harness/Spacer Kit
Posted on Jan 10, 2010
Testimonial: "Thank you for the information it was helpful to know the wire colors, I'll be working on it again later in the week and hopefully get it going."
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