4wd will not engage all the time.sometimes it works great and then it will just quit.it is vaccum engaged and i have checked it and the fluids and they seem to be working.

Check the lubricant/oil/fluid level..

Hi, did you check the transfer case fluid level at all ??

Could also be your metal vaccum lines on the cross member and along the passenger side of the frame to the front axle assembly where they connect to the axle vaccum switch diaphragm. are rusty and leaking not engaging the 4 wheel drive all the way in gear.

check the vaccum hoses, mine would not engage on my truck i have a ford. if there is even these slightest whole in the vaccum line it will not let the 4wd engage. if that doesn't solve the problem check the 4wd actuator. i replaced the hose on mine and fixed it right away..

Hello RD.
Yes, Inside your transfer case there is a clutch that is made up of several plates that are designed to slip when there is a difference in torque between the front and rear.
If improper type of fluid was put in or if the fluid levels were allowed to get low it may have caused damage.
If indeed that improper fluid was put in, drain and refill with the proper fluid.

NVG 136-NP4 (1-Speed Automatic) Auto-Trac II Fluid GM P/N 12378508
NVG 233-NP1 (2-Speed Selectable) Dexron III GM P/N 12346143
NVG 236/246-NP8 (2-Speed Automatic) Auto-Trac II Fluid GM P/N 12378508

Thank you for using FixYa.

KL

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

Did you make sure the transfer case is engaging? Have someone put it in 4wd and look at the front drive shaft see if its turning. If so that means the vaccum switch is either not engaging the lever on the axle hub. Make sure the lever on the axle punkin or gear hub is not sticking. Also check the linkage under the truck.

check the vaccum hses on the back side of the tire if there ok then with the engine running the selector in 4x4 pull the hose off if you hear or feel vaccum on the hose the your iwe is most likely bad on a 07 they cost about 25.00

check the vaccum lines behind your front tires if they are on, with the truck running and lever in 4x4 high pull the line off if theres vaccum then you need to replace iwe. On my 07 its was 25.00

www.amazon.com/Chiltons-Repair-Manual.../0801981425


Hope this helps you

this is most commonly caused by the motor on the transfer case that engages the 4X4 either sticking or defective, sticking can be caused by dirty fluid, have u ever serviced the fluid in the transfer case, it should be done around 30,000 miles if u use the 4X4 allot.