4WD flicks off a bit every once in a while? I haven't used it in a while. Why is that? Cold? ADD going out? Anyone know?! Should I totally take the grease out of the diffs and replace it. What is wrong?


It's a 1990 4Runner with ADD 4WD. I always said once the ADD goes I'm getting locking hubs.

 

Vacuum leak.

Locking hubs won't make a difference (unless you weld the sliding collar in the "engaged" position)

 

like a leaky hose? How do I address this?

 

Ok, anymore help here would be greatly appreciated. I changed ALL of the vacuum hoses involved in the ADD system, from the engine to the axel. It still falls out of 4wd. What should I investigate next. I also found out that a vacuum problem really wasn't the case at all. From what I've found out; when vacuum pressure is applied to place the sliding collar in 4wd, it was stay there until vacuum pressure is applied to move it back, even if there is a sudden loss of vacuum. Obviously, because I have no problem getting into 4WD, there is something preventing the sliding collar from staying in place, or, less likely, something making the vacuum take it out of 4WD.
To further test things, I am going to run a straight vacuum tube from the engine to the locking line of the ADD to permenently lock in the actuator, I am thinking that this will tell me if there is something wrong with the solenoides...
Any thoughts???

 

This should help:

http://personal.utulsa.edu/~nathan-b...26addcontr.pdf

Mike in AR

 

That is a nice guide. I really would like to know if someone had a problem like this and knows what to check.

 

My truck did the same thing. I figured it out but never fixed it.

In the side of the transfer case there is an electrical sensor that senses the position of the shift rod in the transfer case. That sensor is what operates the the vacuum solenoids for the ADD. so when you pull the lever in the cab the transfer case shifts but the ADD doesn't doesn't lock.

There doesn't look like there is much room to work to pull that sensor out. I need to replace my clutch soon, so I'm waiting till I remove my transfer case to fix it.