4WD question

[dannyboy77]

this is more of a question than a problem and kind of stumped my simple mechanic mind. I am currently putting diff breathers on well extending to snorkel and was looking at the toyodiy.com site (fcukin brill I do have to say) and the front diff exploded diagram showed a diff vacuum for the front diff located in the front passenger side wheel arch so when I put it in google it said that the front drive shaft always spins and when you put it into 4WD the vacuum kicks in (don’t know how) and makes the front drive shaft receive torque and hence 4WD. I thought when pushed the 2-4WD lever into 4WD the lever moved a cog in the transfer case and which connected it to the drive train and gave power to the front? Is this correct or not?

[nero279]

both are correct.

It's toyota's automatic disconnecting differential system (A.D.D.)

As in all part time 4wd vehicles yes something happens in the transfer case to send drive to the front prop aswell as the rear when 4WD is selected.

But with the ADD there is also a sliding yoke on the driveshafts which is vacuum operrated and connects the two parts of the shaft together when vacuum is applied to one side, and disconnects them again when vacuum is applied to the other. The principle behind it being to increase economy, and save wear on front end components I believe.

[BUSHWHACKER]

The only way to make it more economical is to fit manual hubs.

The driver's side front CV shaft and diff are always turning even when in 2WD causing drag/poor mpg.
Fitting manual locking hubs disconnects the front wheels from the diff.

There's an electric motor/solenoid on the transfer case that selects drive to the front driveshaft.

[NiftyNev]

I thought when pushed the 2-4WD lever into 4WD the lever moved a cog in the transfer case and which connected it to the drive train and gave power to the front? Is this correct or not?

Not quite as simple as that. Moving the 4WD lever selects low range 4WD rather than high range 4WD when the button is pressed. Other than that the system is still electrically operated as in high range (via the button) through the transfer case shift motor, the 4WD control computer, relay and the VSVs which switch the vacuum on and off for the ADD.

Nev