Vacuum controls for 4x4

[Cessilia]

I have everything running very well but I am positive I have the vacuum lines hooked up wrong. The vacuum on the front differential engager is always under on full.



Does anyone know what the correct vacuum routing is for my truck or where I can find it.



S10 Blazer running a \'90 305 TBI with 700R4.

[Koerbs]

Just tap into the brake bootser vacume line, Thats what I did, Works fine for 20k so far.



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You can see the brass fitting in the line next to the brake booster.

[spacecadet]

Commonly the vac* swith goes bad and either lock the front diff on or when you really need it -off. Theres 3 lines going into to switch 1 is the vent tube which in 2wd allows vac to pass thru and when in 4wd engages front axel. Take a vac gauge and test the positins from both vac lines. If readings stay the same no matter what shifter postion then rotate vac plug to switch and retest. It should relese and stay locked off in any 2/4 postion. If yes then replace switch.

[speeder]

On mine the switch had this 3 pronged adapter on it. It was the problem. I removed the adapter thing from top of the switch and hooked up the lines directly to the switch. Then I tested the lines I think 1 held vacuum and the other two did not. So one of the two was the vent the other was the line that hoked to the manifold right next to where I hooked up the AC blower-fan controller line on the intake. Then I shifted the transfer case into 4X4 now the one that held vacuum did not and the other two were connected. Now the vent held vac*. So I just used some deductive reasoning and BAM she worked. It took me about 3 days of thinking about it before I realized what to do, but my 4X4 worked great, until I took it off.

[evil_admin]

Basically you have 3 ports. One is a vac source, one is vac out (or in if your a half full kind of person) that goes to the central locking feature plunger and the 3rd is a vent. The system works by sealing the input when the xfer case is in 2hi only. Also in this position, the output to CLF plunger is connected to the vent. When you enter 4(hi,lo,neutral) the vac is diverted to the CLF plunger and disconnected from the vent.



When you exit 4 and go back to 2, the CLF plunger hose is connected to vent and vac supply is sealed. If it did not vent the CLF plunger, it would stay on all the time until you unplugged the hose from the plunger.



These valves are not cheep and must be bought from a dealer. Parts stores dont have them. Saw a guy on ebay selling them for $30. Search for \"4x4 valve\" or something like that.



To figure out what hose goes ehere, start by finding what hose is sealed when in 2hi. Once you find that one, pull it into 4hi. That line should no longer hold vac. Now, look to see which of the other 2 lines now have vac. You can do this by connecting the source line to a vac pump or running engine (BEWARE!!) then placing finger over the hose. (If you do this on a running engine, use wheel chocks and put xfer case in neutral.)



Now, you have 3 hoses found, a source, a switched vac and one that is doing nothing. Connect the source to the main vac line off the manafold. Brake booster is a good place. Connect the switched line to the CLF plunger. Connect the 3rd hose that does nothing to the xfer case vent and bring that up to the front left of the rad support. (there is a water proof vent there)



Another thing you can do is connect a manual pull cable to the CLF cable. That way if you out in the woods and rip out your vac lines, you still have 4x4.



Oh, heres a little tip. Keep a C clamp in the cab big enough to pull the plunger all the way in. Backup 4x4 starter wigit.