4x4 will not engage please help

[kingtim]

i have an 86 blazer and when i shift it in to 4 wheel drive the shifter lights move as i shit it however the little light that shows the front wheels on doesnt light up, nor does it engauge, i checked the vacuum actuator and it seems to be workgin properly is there an easy way to test why its not working or any ideas WHY woudl be helpful its zegitive 2 outside and we ahve 6 inchs of snow, i really would like to get out of my driveway Thanks inadvance
--tim

[vtmecheng]

So the vacuum actuator is working and is pulling the cable connected to the diff. Jack the truck up on the passenger front side. In 2X4 check to make sure the wheel spins free. Then start the truck up, put in 4X4, and check to see if the wheel spins. It could be either the light is out or the sensor in the front diff is not working. If the wheel spins free in 4X4 then you know either the actuator is bad, vacuum lines leak, vacuum switch (on transfer case) is bad, or cable is frozen (good possibility with -2 outside). Good luck and let us know how things went.

[kingtim]

well, part of the problem im having is i dont fully understand HOW things are saposed to work, therefore i cant work on fixing the problem, its too cold today to jack it up i did that yesterday however i didnt turn the truck ON so, if you could give me an idea of how all the parts are sapoose to work, that would also be helpful, Thanks
--tim

[jackson5]

I have been going through this same drill with my 91 s10 blazer. Here is how it works. You push the floor shift to 4 wheel drive. This activates a small vacuum switch on the transfer case which sends suction through a vacuum hose to a vaccum actuator located underneath the battery box on the right font of the car. This actuator then retracts a cable when a suction is applied. The cable goes into the front differential and is connected to a shifting fork. This fork moves an inch or so and couples the right front axle to the left front axle. There is a switch located on the cable housing on the differential that turns on the light in the drivers compartment showing that it is in 4 wheel. drive. Now These vacuum set ups are not to relable. Here is how you can check your differential. Unfortunately you would need all wheels off the ground. You can disconnect the differnential cable from the vacuum actuator (located under the battery). with the engine running and the car in reverse and in 4 wheel drive ( you don't want it to run over you if it comes off the jack stands). Pull on the actuator end of the cable with pliers and see if it goes in and out of 4 wheel drive as you pull. If you push the cable it should go out of 4 wheel drive. if all of this is working you are in luck! you simply have an inexpensive problem in the vacuum system, that pulls the cable. You will have to check it out. pull the vacuum hose off the actuator under the battery and see if you have suction. if you do and the actuator isn't moving you have a leaking vacuum actuator. If you don't have suction you either have a rotten vacuum line or a faulty vacuum switch located on the transfer case.

I wasn't so lucky I had a mechanic pull my differntial today. and will have to install a junk yard differntial tomorrow. $125-$175 for the differntial and $200-250 for the labor. Good luck.!

[jackson5]

I forgot to mention that there is an aftermarket kit on the internet that will replace the complete vacuum system with a simple pull cable mechanism similar to an old fashion choke cable. It cost about a $100. You manually engage the transfer case as usual then you pull the handle on the cable mechanisim (you mount it in a convinent location under the dash) when you pull the cable by hand it will pull the cable to the front differential. Pretty slick and you don't ever have to worry about this crappy vacuum system failure. here is a link that explains the system and the fix. http://www.4x4posi-lok.com/inst_tsg.html

[vtmecheng]

I tried that posi-lok crap, DONT BUY IT. While it will probably work, I didn't trust it. I mounted it on my truck, had it all set up, and tried it out but found one problem. Because they wanted to make the part work for multiple vehicles it was not quite a correnct fit for my truck. Either engage or disengage was at the absolute extream (depending which hole I used) never giving me a feeling of full on or full off. This could cause the dog tooth gear to strip out in the differential. I ended up returning it.

[Mushroom777]

SAME HERE that light that shows ALL 4 tires lit up dones not work on mines either ? :-( any way too make it WORK