4wd Problem, Please Help

[mike8578]

Hello, I have a 99 Blazer LS 4door. My 4wd just stopped working the other day. When i hit the button to engage it. The front tires are not engaging. The rear are engaging. Don't know much about, friend of mine said its plugged in, and all vacumes appear to be plugged in. What are some things to check, or possiblities of this problem, any help is greatly appreciated. Thanks in advance.

[old_master]

3 or 4 button switch on dash?

Do the lights in the switch blink when trying to shift into 4WD?

Does the transfer case make any noises when trying to shift into 4WD?

[mike8578]

Hello, it has 3 buttons. 2wd, 4low, and 4 high. No when you push whatever they stay solid. No noise other than the rear engaging that I can tell of.

[old_master]

The rear wheels are always engaged. If you're hearing something from the transfer case, the TCCM, (Transfer Case Control Module) is commanding the encoder motor to shift the transfer case to 4WD. I'll take that one as a "yes"

Next step, you'll need an assistant for this one: With the engine idling, check for vacuum at the actuator under the battery tray when attempting to shift into 4WD. NOTE: Vacuum may only be momentary when attempting to shift into 4WD.

If vacuum is applied, can you see the cable pull in? The cable operates a clutch on the right front axle shaft which engages it with the front differential. (The left front axle shaft is always engaged with the front differential.) When the right axle is engaged with the differential, the front differential becomes "live" and the 4WD is operational.

[MikePathfinder2001]

Man, I've had a similar problem with mine for years. Every so often, my 4wd accuator (located under the battery) corrodes and is left not working properly. The car would say it was in 4wd, but is wasn't. Anyway, you should check that (as stated in an earlier post). You will probably need to just replace it and you will be good. I read a very good post on how to do that on this forum, but if you just take that battery out and (unfortunately) the plate that holds it. (I couldn't totally get my plate out and had to bend the rusty bastard). Anyway, there are like only 3 screws that hold it in. Just remove and replace. The tricky part is latching the wire in the actuator. Anyway, I bet that will fix your problem.

[mike8578]

Hello, just wanted to let ya know. pulled battery and checked actuator under there. Had a rip in the boot, changed that, 4wd workes great again. Thanks for all your help, greatly appreciated!!

[old_master]

Glad you found the problem and thanks for posting the fix.