I have a 1995 chevy blazer two door with a manual transfer case. Through due diligence and repairing I have installed a new vacuum actuator, a new transfer case shift cable, and a new vacuum switch. Everything seemed cool until it snowed last weekend. Four wheel drive seems to be working at low speed as I tried to make a tight turn to test it and it tightened up. But when driving under acceleration the lights on the front wheel indicator go out. Let off the gas and they come back on. Any ideas. Hopefully I gave you enough info.

 

There's a vacuum leak, or a faulty vacuum check valve. Check the vacuum lines, the check valve, and vacuum reservoir.

 

Where would the check valve be?

 

Follow the vacuum line from the intake manifold. Should look similar to this:



The larger fitting goes toward the vacuum source, (intake manifold). One of the smaller ones go to the reservoir. The other small one goes to a TEE. One side of the Tee goes to HVAC & the other side goes to the vacuum switch on the transfer case. If the check valve, reservoir or lines are leaking, it will cause the HVAC airflow to go to defrost, and the front axle to disengage, when manifold vacuum is low, (up hills etc). Another possibility is a leaky diaphragm in the axle actuator, (under the battery tray).

 

Reservoir being the ball correct?

 

On 95, yes, round black plastic ball.

 

Diaphragm is good. Tested it last night. So thinking line or check valve. Any suggestions on the best way to test.

 

The vacuum switch on the transfer case has 3 vacuum lines in one connector. It is keyed so it will only go on the switch one way. It is possible to put it on so the key doesn't line up. If it's not on correctly, the actuator will not get vacuum when it should, and it won't vent when it should. You'll need a mirror and a flashlight to make sure it's plugged in correctly.

If that checks out ok: With the engine at idle, unplug the vacuum connector, one line should have vacuum.

One lines goes to the actuator. If you apply vacuum to it the actuator must pull the diaphragm and hold vacuum.

The third line is a vent and should be clear at all times.

EDIT: From your first post: This has "vacuum problem" written all over it: "when driving under acceleration the lights on the front wheel indicator go out. Let off the gas and they come back on".

 

Would changing the lines out be a good idea. 221000 miles on the clock

 

Changing the lines would make sure that the lines are OK, (no leaks or restrictions). Just make sure they are routed correctly from the vacuum switch.