Gday out there.
My 89 4runner wont engage 4wd in hi or low range. When the switch\button on the side of the hi\lo selector stick is pressed, you can hear the electrics ungerneath at the t/case working fine tho she still wont engage the front axle. With all wheels off the deck and in all gear\range combinations, only the rear wheels are rotating. The 4wd light doesnt illuminate and the hubs arent the manual locking type. Any experience on thi matter would be appreciated. Thanks

 

My best suggestion as to find out what's going on would be to jack the front wheels off the ground, turn the ignition on without starting the engine, and then play with certain things under the truck while turning 4WD on and off.

For example, first try to rotate the front driveshaft and see if it rotates freely with 4WD off. Then push the button so it shows it's engaged, and try and turn it again. If the back wheels are still on the ground and immobilized, the front driveshaft should not be able to be moved with the transfercase engaged. that'll tell you if the problem is in the T-case, or in the front hubs.

 

Is yours a manual trans or auto? Sounds like an ADD problem though, plenty of information about it

 

take the steps to determine if it's at the front diff or the t-case. if you're getting zero movement at the front axle, i'm guessing it's tcase related. if the tcase were functioning properly, you will still get the front driveline and front passenger axle to move, since that axle is permanently fixed with drive flanges (non-manual hub)

if your front driveshaft moves and the driver's side axle doesn't move, then it sounds like it's related to the ADD mechanism. make sure all the vacuum lines are installed and intact, so they engage the driver's side shaft.

 

If the ADD is disconnected, neither front axle shaft will move even if the front drive shaft is turning. The differential spider gears just spin internally (they're very low friction), the ADD stub shaft turns (which you can't see), and no power is transmitted to either axle.

 

As JasonYota and RJR suggest, this sure sounds like an open ADD. Seems the most commonly reported problem is a disconnected vacuum line to the front differential. Visually check that they are connected. If they are, disconnect one (or both) and with the engine running (to create vacuum) and the parking brake on (to prevent getting run over) use your thumb to test for vacuum as someone shifts the transfer case.

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

 

What year is this truck again? I guess I was referring to the 89 and down models that don't have the disconnecting differential.

 

OP's truck is an '89. According to Wikipedia, ADD came out in '89 so could be involved in the problem.

 

Thanks for yr help guys.
Ran new vac hose/line direct from manifold to ADD? module on front axle.
INSTANT RESULTS.
Very greatfull.

NEXT QUESTION... TYRES.
Generaltire GRABBER AT2

From what i can find,in Australia they are (as with most tyres), nearly double the price as what you guys in overseas are charged.
Kinda makes tyre choice in oz a bigtime PITA!!