Front transfer case wont engage 4x4 on 95 chevy k1500

Replace the solenoid switch on the front diff.

That truck did not use a vacuum actuator, it used an electric motor motor. If your transfer case is engaging and you can see the front drive line spinning, then you either have a bad actuator, switch, or the wiring is bad. I would recommend unplugging your actuator and checking for power at the wire while someone puts the truck in four wheel drive. If there is power going to it, then replace your actuator. if not, follow your wiring back and check all components. They also sell an aftermarket cable actuator for those trucks which are much more reliable.

There are 2 models here the push button will flash if the system is not engaging or disengaging properly . If front drive shaft is turning. That is with car raised and supported . if front drive axles do not turn then the axle actuator is not engaging axle shaft passenger side. Remove actuator and manually engage shifting collar with a screwdriver still does not turn then inner axle is twisted.

Make sure that the vacuum hose connector is connected AND connected correctly at the transfer case and at the front differential. If that is all right and the front differential still doesn't engage, then you need to test the vacuum actuator at the front differential.

The Selectable Four Wheel Drive (S4WD) Front Axle consist of the following components:
• Differential Carrier Housing
• Differential Case Assembly
• Inner Axle Shaft
• Intermediate Shaft Bearing Assembly (located on the right side of the oil pan)
• Electric Motor Actuator
The front axle on Selectable Four Wheel Drive (S4WD) model vehicles uses a disconnect feature mounted on the right side of the oil pan in order to engage and disengage the front axle. When the driver engages the 4WD system, the Transfer Case Control Module sends a signal to the electric motor actuator to energize and extend the plunger inside. The extended plunger moves the clutch fork and clutch fork sleeve across from the clutch fork outer gear that is splined to the right side wheel drive shaft to the clutch fork inner gear that is splined to the inner axle shaft. The locking of the two gears allows the axle to operate in the same manner as a semi-floating rear axle. A propeller shaft connects the transfer case to the front axle. The differential carrier assembly uses a conventional ring and pinion gear set to transmit the driving force of the engine to the wheels. The open differential allows the wheels to turn at different rates of speed while the axle continues to transmit the driving force. This prevents tire scuffing when going around corners and premature wear on internal axle parts. The ring and pinion set and the differential are contained within the carrier. The axle identification number is located on top of the differential carrier assembly or on a label on the bottom of the right half of differential carrier assembly. The wheel drive shafts are completely flexible assemblies consisting of inner and outer constant velocity CV joints protected by thermoplastic boots and connected by a wheel drive shaft.

How To Install Repair Replace 4x4 Front Axle Actuator Chevy Trailblazer...

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.

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. The actuator may not be fully engaged or disengaged and the fork to the spline may be what is causing the whining or grinding noise you hear.

88-UP C/K ACTUATOR UPGRADE
VEHICLE SERVICED: 1994 CHEVROLET FULL SIZE
PURPOSE: IMPROVE AXLE CONNECT ENGAGEMENT TIME AND
COMPONENT RELIABILITY.

SYMPTOMS: NO FRONT DRIVE AXLE ENGAGEMENT WHEN SHIFTED INTO 4X4.

Obtain the following GM part numbers:
(1) 26060073 Actuator
(1) 88959465 Harness/Spacer Kit

If you haven't got 12volts at the actuator(TLA) plug, then you are probably correct from what I have researched as well.
I have found a solution to the problem that would eliminate the need for 12volt power or a TLA.
http://www.4x4posi-lok.com/app_chevy-k.html
I keep blowing fuses on my 1997 GMC K1500 and think this switch may be the culprit for me as well.

Sounds like the chain in the transfer case has broke or the linkage is out of adjustment

The vacuum switch on the transfercase is most likely the problem. If you remove it and the plunger is stuck in, replace it and your 4wd should engage again.

I had the same problem on my 90 K1500, it was the 4 wheel drive actuator unit itself. Bout it at the local parts store for 30 bucks and installed it in 10 minutes or less - and vavoom! 4 X 4 back in business.