When i engage into 4 wheel drive the axle spins and the c/v joints spin but not the front wheels.

awd drive cars have a differential action between front and rear wheels and there should be a switch that allows you to lock up that action for adverse conditions
if the rear wheels are not working , it is because there is no drive action to the front wheels ( front wheels spinning or broken drive shaft to the front)
all wheel drive means that in normal driving when there is traction on all 4 wheels that the power is transmitted evenly to all 4 wheels
It is not 4 wheel drive where power is applied to both axles or in the event of one axle loosing traction the other axle still drives

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...

First, start checking the fuses an there is also an electrial activaced switch at the transmission or transfer case that may be bad.

95-96
Your control knob should say 2wd, 4auto, 4low.

First, we need to narrow it down to a transfer case issue, or a front axle issue.
Step 1) Jack up the front end and place it securely on jack stands.
Step 2) Verify that the front driveshaft turns by hand. When turning the front driveshaft by hand, the front wheels may or may not turn. Do not be alarmed if they don't turn. This is normal for your vehicle.
Step 3) Start the vehicle and let it idle. Place your foot firmly on the brakes, place the transmission in NEUTRAL, engage 4low, then place the vehicle back in park. DO NOT ENGAGE ANY GEAR!! The lurch as the transmission engages could cause the vehicle to lurch and potentially fall off the jack stands.**If you can turn the front driveshaft, the transfer case is not locking. This could be due to a mechanical issue with the transfer case itself, or an electrical gremlin with the control system. Start a new thread with the results of your checks, and we'll go from there.
**If the front driveshaft does not turn, the transfer case is locking properly and we need to continue searching.
Step 4) With the front wheels in the air, engine idling in PARK, spin one front wheel. The other wheel should spin the opposite direction. If both wheels spin in opposite directions, then the front axle *should* be properly engaged. Take it for a test drive (after safely lowering it to the ground, of course). If the front wheels do not spin in opposite directions, there is a problem with the front axle. This could be due to a mechanical problem with the diff, or a failure of the center axle disconnect to engage the passenger side axle shaft. Start a new thread with the results of your checks, and we'll go from there.

Troubleshooting the CAD on a 95-96 is a bit more involved than I want to get into here, and the problems can vary widely. This'll get you started.


97-01 4-door and 96-00 Sports
Your control knob should say 4auto, 4high, 4low.
First, we need to narrow it down to a transfer case issue, or a front axle issue.

Step 1) Jack up the front end and place it securely on jack stands.

Step 2) Verify that the front driveshaft turns by hand. When turning the front driveshaft by hand, the front wheels should turn. (If only one turns, don't be alarmed. One wheel sometimes has more resistance in the brakes, bearings, or CV joints. This is normal)
Step 3) Start the vehicle and let it idle in PARK. Engage 4high. DO NOT PUT THE VEHICLE IN GEAR!!! Crawl underneath and see if you can turn the front driveshaft.
**If you can turn the front driveshaft, the transfer case is not locking. This could be due to a mechanical issue with the transfer case itself, or an electrical gremlin with the control system. Start a new thread with the results of your checks, and we'll go from there.
**If the front driveshaft does not turn, the transfer case is locking properly and we need to continue searching.
Step 4) With the front wheels in the air, engine idling in PARK, spin one front wheel. The other wheel should spin the opposite direction. If both wheels spin in opposite directions, then the front axle *should* be properly engaged. Take it for a test drive (after safely lowering it to the ground, of course). If the front wheels do not spin in opposite directions, there is a problem with the front axle. Start a new thread with the results of your checks, and we'll go from there.


'01-'03 Sport and '01-'05 Sport Trac
Your control knob should say 2wd, 4high, 4low

The transfer case in these trucks functions essentially like the 1st-gens' 13-54 t-case. (i.e. it uses a lockup collar engaged by the transfer case shift motor) The troubleshooting procedure is very similar, but you don't need to worry about hubs or center-axle disconnects engaging.

Step 1) Jack up the front end and place it securely on jack stands.
Step 2) Verify that the front driveshaft turns by hand. When turning the front driveshaft by hand, the front wheels should turn. (If only one turns, don't be alarmed. One wheel sometimes has more resistance in the brakes, bearings, or CV joints. This is normal)
Step 3) Start the vehicle and let it idle in PARK. Engage 4high. DO NOT PUT THE VEHICLE IN GEAR!!! Crawl underneath and see if you can turn the front driveshaft.
**If you can turn the front driveshaft, the transfer case is not locking. The shift motor could be falsely reading an incorrect t-case position, or it could be a mechanical issue with the case itself. Start a new thread with the results of your checks, and we'll go from there.
**If the front driveshaft does not turn, the transfer case is locking properly and we need to continue searching.
Step 4) With the front wheels in the air, engine idling in PARK, spin one front wheel. The other wheel should spin the opposite direction. If it does, the system should be properly engaged. Safely lower the vehicle to the ground and take it for a test drive. If the wheels do NOT spin in opposite directions, there is a problem with the front differential or axle. Start a new thread with the results of your checks, and we'll go from there.


Keep us updated.

Check the transfer case. Put a jack under the rear axle and jack up the rear wheels. Have a helper put in 4 wheel and the trans in drive. Have him/her ease off the brake and see if the rear wheels spin. If they spin, 4x4 isn't working. If the truck tries to pull forward with the rear wheels up then it works. Now, if the rear wheels are spinning carefully look under the truck and see if the front driveshaft is spinning along with the rear driveshaft. If the front shaft is spinning then it is an axle problem. If the front shaft is not spinning then it is a transfer case problem. GM has a problem with the NP263 case.

CHECK FOR VACCUM AT THE HUB IF YOU HAVE VACCUM THEN ITS SOMEWHAT COMMON FOR THE LOCKING HUB TO WEAR

Two things maybe your problem:1 .Front axle actuator to engage 4wd is not releasing. 2. Front axle u-joint needs replacing. Lift car on jacks with front end off ground. Then spin tires by hand as fast as you can and see if you hear the noise and where it is coming from ( spin in both directions).

Having 4 wheel drive is not actually the case unless you have limited slip on both axles. Do you know if one wheel will spin on both axles. If you can't get either wheel to spin on the front axle and one will spin on the rear then I would agree your not getting front wheel drive. Since you can tell a difference between hi/lo the transfer case is definitely engaging

shift into 4wd and move truck a couple of feet.
if light is still off, park truck block the wheels set the park brake jack right front wheel and try to hand spin the wheel if wheel doesn't turn 4x4 is functioning properly but there is a wiring problem use an ohmmeter to check the 4x4 switch wiring fuse and bulb
if wheel turns freely the front axle or transfer case is not engaged
attempt to hand spin the front driveshft if the driveshaft will spin the transfer case is not engaged check the transfer case shift linkage, problem is in linkage or transfer case internals
if the driveshaft will not spin the transfer case is engaged properly
with trnsmission in neutral or park start engine measure vacuum on the two vac lines at front axle shift motor . one line should have approx 20" vacuum. other line should have none
if no vacuum measured look for vac leak or bad vac switch
if both lines have vac look for a bad vac swithc or ruptured cad actuator diaphragm
if one line has 20" +- VAC
move transfer case lever to 2wd measure vac again lines should have swapped vac signals
if no vac switch bad or 4wd shift likage needs adjusting
if yes vac motor bad or stuck or shift fork stuck
remove vac shift motor from the axle attach vac lines to shift motor engage disengage 4wd
does shift motor plunger move at least 1/2 inch
no shift motor bad
yes check axle shift fork and vac motor for binging

Test it by setting the rear end up just barely off the ground with some jack stands and setting the hubs to lock (if they are manual). Put it in 4 wheel and try to drive away. If the vehicle does not move then very carefully have a helper check and see if the front drive axles are spinning while it is in 4 wheel and in gear while running.
Spinning axles... hubs are at issue
No spinning axles... Transfer case issue.

Could be a few things. Bad ball joint, cv joint, or others. But I'ld start with the CV joints. Basically, your axle shaft. First way to tell if that's the prob would be to put truck in 4 wheel drive, LOW gear. This will lock up all four tires. Then jack up that corner of truck. If the tire only moves a little before you can't anymore, it's fine. But if you can spin your tire completely, odds are it's your cv joint.