Yesturday I noticed my left hub was not locking and was making a spinning noise anybody have any thoughts?
Thanks tahike

 

Your 99 does not have auto hubs, its has ADD. The hubs are always engaged to the axle. The noise is coming from something else.

 

What does add stand for? thanks

 

This may give you a little bit of insight:

http://www.hunt4steve.com/99RunLtdIFS_Shafts.html

http://www.hunt4steve.com/99RunLtdDT.html#hubs

Here is the page to the FSMs for the 99 4Runner. Read em
http://www.hunt4steve.com/99RunLtdFsm.html

 

Automatic disconnecting differential.

Its a vaccum actuated mechanism that locks and unlocks power to your axles.

Like Cougar said, you dont have "hubs" like the older trucks do. Its set up like front wheel drive CV's are set up. THe CV axle goes directly into the splined wheel hub with no moving parts.