Hey everyone,

First post on the forum but I have been reading/researching for quite some time. the 4wd thread that user "Hanr3" posted is a good detailed explanition of how our system works.

I have been having issues with my 4wd and have finally gotten around to diagnosing it. Detailed below is where my 4wd system stands as well as the steps I have taken to fix the 4wd:

Currently when i press the 4hi button the switch will send signal to the TCCM; TCCM will send signal to encoder motor and engage the transfer case. The front axle will spin at this point.

4wd Maintenance performed:
• Replace encoder motor
• Replace TCCM
• Replace dash switch
• The vacuum actuator under the battery does move when the 4wd button is pressed, I am not sure how much it is supposed to move to diagnose if the engine is creating enough vacuum.

I believe my next step would be to replace the vacuum switch on the transfer case. Last night I unplugged the hose on the switch and could feel vacuum out of 1 hole. Is it possible I do not have the hose plugged into the right holes on the switch?

I should note that when I took the vacuum hose off of the vacuum switch there was oil in/around the hose.

I read about engaging the front hubs manually by using vice grips on the actuator cable. If i can get it into 4wd this way would that narrow my problem to either the actuator itself or the vacuum hose?

Before I go and buy a new vacuum switch tonight does anyone have any other suggestions?

Thanks for the help.

 

The actuator under the battery should pull the cable 1/2" to 3/4" when vacuum is applied.

A vacuum gauge should tell you if you have a vacuum leak somewhere in the vacuum system between the engine & the actuator.

 

The cable probably moved between .25 and .5inch. I am going to try using the vice grips to engage the 4wd and see what I come back with. So two scenarios:

what are my next steps if a) 4wd engages by manually pulling the actuator cable and b) if the 4wd does not engage?

It seems if the 4wd does engage by pulling the cable manually that tells me there is not enough vacuum coming from the engine in which case I most likely have a leak in a hose somewhere?

If the 4wd does not engage by pulling the cable, what's next, replace the vacuum actuator or does the test of pulling the cable bypass the vacuum actuator entirely?

Do I still want to change the vacuum switch first?

 

If the 4wd engages when you pull the cable and you are getting vacuum to the actuator, replacing the switch is likely not necessary. You may have to replace some vacuum line though. Testing the vacuum at the switch as well as at the actuator (with the 4wd engaged) and comparing that to the vacuum level at the engine will tell you if you have a leak.

If the front axle still does not engage, then there is a problem either with the cable itself or inside the front axle itself. If the cable moves freely when disconnected at the front axle, then you'll need to pull the passenger side extension housing off to get access to shift fork and associated parts inside.

 

Attached is a picture of the actuator: Do I want to pull from #1 or #2 and I want to pull towards the actuator correct?

 

The rusty portion is what you want to pull on. From the picture, it looks as though the actuator bellows (rubber portion) might be broken.

 

Thanks, that isnt an actual picture of mine, taken from the link to the posi lock diy 4wd thread. After reaching my hand down there I'm not sure how i'll get vice grips all the way to that position... that is assuming this needs to be done with the vehicle running and in 4hi; so having the battery installed.

 

Try disconnecting the cable from the actuator and the cable bracket and then use some pliers to get it moving freely. Mine would only move 1/4-1/2" and after I worked it loose it now moves 3/4-1" and engages properly

 

Ok thanks I'll give that a shot. Did you lube up the cable at all? My 4wd has not been engaged in quite a while so the cable could well be very tight.

 

yea, I sprayed some pb blaster inside the cable to help loosen it. Wouldn't hurt doing it where the cable goes into the axle housing as well although I didn't since I didn't have the truck jacked up at the time