4wd automatic locking hubs

how can i test to make sure my hubs are completely disengaged even if my light goes off im getting 15 mpg and wondering if maybe the 4wd is not completely disengaging im new to the taco family as well as this site wondering if anyone else is having this problem

 

If your truck has the ADD system it is the differential that is disconnected. On an ADD (Automatic Disconnect Differential) the wheel hubs are always engaged. To test this, you should be able to turn the front driveshaft by hand if the front axles are disconnected from the differential. This would be correct behavior when the ADD is off.

 

My recollection of the front ADD diff seems to disagree with this . Both front axles are not disengaged from the front diff. There is a collar and fork on the passenger side tube that engages/disengages the passenger side cv axle. The driver side is always connected to the differential which causes the front driveshaft to rotate. This in turn keeps the front output gear and the rear output gear aligned for "Shift on the fly 4wd". To confirm that the 4wd is disengaged you would have to lift the front end and spin either driver side or passenger side tire. If the otherside spins then the collar is engaged and still 4wd, otherwise it is disengaged.

Or you can just trust that the engineers at toyota were right with the light

 

You are correct about the pass side axle being the side that is disconnected. But that does not change the way the front driveshaft behaves when the ADD is off.

When you rotate the front driveshaft by hand, the passenger side of the diff still turns freely. It does so because the diff is 'open', so everything is transfered to the path of least resistance.This means the front wheels don't have to be off the ground to test whether the ADD is in fact disconnected.

 

Start the engine, get on the pavement, turn the steering wheel all the way to the right or left, put it in first gear and let out the clutch. If the truck jerks and binds up while you idle through the turn, your ADD is ENGAGED. If the truck turns smoothly, your ADD is NOT engaged. Won't take much, just15 to 20 feet and you'll know.

 

Hi Capt.,

So it is clear... the idea of an ADD vs. auto locking hubs is basically the same: to reduce front end wear, increase mileage.

Auto hubs (my dad had them on his '65 Jeep) can be shifted into, on-the-fly, but for them to disconnect you had to drive in reverse a bit.

An ADD allows to go into and out of 4WD-HI while driving (shift on-the-fly) and frees up a lot of front end wear.

ADD disconnects on one side of the differential, just like when one tire gets off the ground or in mud, it spins and the other tire does nothing... so no 'power' or rotation goes to the front end and both half axles are free spinning.