When I first bought my Jimmy, the 4wd worked fine. After I installed the lift and tires, my front wheels wont spin. When I installed the body lift, one of the steps was to remove the vaccum pump under the battery tray from the firewall.(Im assuming this pump is for the engage/disengagement of the front axle.
When I press the 4hi button I get a small motor noise and a slight clunk at the transfercase. When I put it in 4lo, I get an even louder clunk noise. In 4lo, Myengine revs high to make it move(just like its supposed to) but my front wheels dont spin.
Mabey its the pump I removed and put back on? How do you suppose I check this pump? Ive read of putting your finger over the vaccum line to feel a suction......????

 

It isn't a pump. It is a vacuum actuator. Engine vacuum pulls on the diaphragm in the actuator which pulls on the cable to engage the front axle. The actuator requires engine vacuum supplied from the vacuum switch on the transfer case. For this to work, the other end of the actuator (cable end) must be connected to the front axle so that it can pull on the engagement mechanism.

First, verify that everything is connected properly. Then verify that you have vacuum at the actuator when in 4wd & engine running (a vacuum gauge works great here).

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So the noise and engine rev that I hear in 4lo and 4hi are pretty much guarantees that its just the front axle thats not engageing???? I will check thoughs and let you know.