97 Blazer Front Differential Problem

[joeclarktoyota]

97 S10 4x4 Blazer, 4.3 V6 (not ZR, just std). Front differential not engaging. I jacked up all four wheels, push the 4H button and I hear a clunk and the drive shaft going to the front differential engages but front wheels don't turn. I unhooked the three bolts that hold the acuator cable in the differential but didn't unhook cable. I pulled on the plate/cable and the front differential engaged, front wheels turned, no noise. I checked the vaccum acuator with cable disconnected and it moved thru the full range of motion. I unhooked the cable from the differential and when 4H is pushed the acuator pulls the cable thru full range of motion. No apparent vaccum leaks, but when I hook everything back up and push the 4H button, the front wheels don't turn. There was a clicking sound coming from front differential when like it was trying to engage but couldn't.

Update: I installed a new vaccum actuator, flushed and changed the differential oil, still only way I can get front differential to engage is to assist the actuator by squeezing in on it with my fingers. I'm thinking it must be low vaccum. Where does the vaccum come from? The hose runs to the back of the engine then it's hard to trace, looked like it was going toward back of the vehicle, but I need to follow it all the way back to source of vaccum.

Any help would be appreciated.

[old_master]

Sounds like you're on the right track...low vacuum to the actuator. There is a vacuum switch on the transfer case with 3 ports: One goes to the actuator under the battery. One vents to atmosphere and is usually attached to the transmission dipstick tube and has a small filter on the end of it. The third goes to a vacuum reservoir under the hood, and has a "Tee" and check valve then goes to intake manifold vacuum. Some systems use an electric solenoid, in which case it is mounted to the firewall, a little right of center. The vacuum switch on the transfer case can also develop a leak. Hope this helps.

[joeclarktoyota]

Thanks for the info. I'll let you know what I find. Again thanks for the help, these forums sure do help.

[joeclarktoyota]

I found the problem. Traced out all the vacuum lines and the one going to the canister mounted on bottom side of hood was the problem. Replaced the line and it works like a charm. A $3.00 fix !!!!

Thanks Old Master for the details you provided.........Joe

[old_master]

Glad you found it, and thanks for posting your fix.