Question about A.D.D. System

[JZiggy]

this video is of a hilux surf but doesn't show the counter rotation. is this different then the 3rd gen? https://youtu.be/nIJwEn_0CPo

Starting at 10 seconds you can see that when the ring gear is not moving the two sides spin in opposite directions.

 

[JZiggy]

It doesn't have to be too confusing. Sadly, the video shows the 'uninteresting' version of the ADD system. If the diff side stub was spun, you would see the side gear out to the ADD sleeve spin opposite direction from the side with force applied.

Here are a few situations:

Driving slowly, 2WD: Driver's side diff side gear spins with CV axle, disconnected side spins opposite direction, ring/pinion is stationary. At the ADD sleeve, the two 'sides' are going equal and opposite directions.

Driving quickly (say, freeway speeds) 2WD: Same as above, but enough viscous force is applied to the ring gear/carrier by the spinning side/spider gears that the ring spins a bit. The prop shaft will spin, but much slower than it would if the ADD is connected. It is free to move at whatever speed it 'feels like'.

4WD: Everything is locked together, uninteresting for this discussion.

Shifting into 4WD while moving: The ADD system does not engage until the transfer case shifter is in the 4WD position. There is a synchro on the 4WD shift sleeve in the transfer case, which applies torque to the front prop shaft to spin it up to the speed of the rear prop shaft. This is why as the transfer cases get older, they get harder to shift into 4WD - the synchro gets worn out! When the front prop shaft and the left CV axle are spinning at the same speed, the right diff output will also spin at the speed and direction of the right CV axle/stub shaft. At this point, the ADD can engage without trouble (the splines are are basically going the same speed).

Hopefully that clears it up a bit.

-Charlie

Perfect explanation. The transfer case has a synchro which speeds the prop shaft up to match the speed of the rest of the driveline. Once it is locked up then the ADD tube "knows" that it can lock up too because it's two components are now running at the same speed (and direction!)

Thanks Charlie!

 

[mtbtim]

It doesn't have to be too confusing. Sadly, the video shows the 'uninteresting' version of the ADD system. If the diff side stub was spun, you would see the side gear out to the ADD sleeve spin opposite direction from the side with force applied.

Here are a few situations:

Driving slowly, 2WD: Driver's side diff side gear spins with CV axle, disconnected side spins opposite direction, ring/pinion is stationary. At the ADD sleeve, the two 'sides' are going equal and opposite directions.

Driving quickly (say, freeway speeds) 2WD: Same as above, but enough viscous force is applied to the ring gear/carrier by the spinning side/spider gears that the ring spins a bit. The prop shaft will spin, but much slower than it would if the ADD is connected. It is free to move at whatever speed it 'feels like'.

4WD: Everything is locked together, uninteresting for this discussion.

Shifting into 4WD while moving: The ADD system does not engage until the transfer case shifter is in the 4WD position. There is a synchro on the 4WD shift sleeve in the transfer case, which applies torque to the front prop shaft to spin it up to the speed of the rear prop shaft. This is why as the transfer cases get older, they get harder to shift into 4WD - the synchro gets worn out! When the front prop shaft and the left CV axle are spinning at the same speed, the right diff output will also spin at the speed and direction of the right CV axle/stub shaft. At this point, the ADD can engage without trouble (the splines are are basically going the same speed).

Hopefully that clears it up a bit.

-Charlie

Thanks for this explanation. By the way, how do you know all this stuff Charlie? You seem to chime in regularly with the answer to how shit works.

 

[phattyduck]

Thanks for this explanation. By the way, how do you know all this stuff Charlie? You seem to chime in regularly with the answer to how shit works.

All the information is out there, just in little bits and pieces spread all over. The challenge is putting all those pieces together (that's kinda what I do for work as an engineer) I love learning about basically anything car related, and I'm just happy to share knowledge after I have learned it.

Heck, before I got the 4Runner, I didn't really even know how a 4WD system works! I was even kinda confused with the 4WD shifter until I messed with it and read about what is going on in the case...

-Charlie

 

[Tyler James Inc]

Yeah- with the carrier/ring/pin stationary- if one axle is spinning, the other is absolutely spinning opposite at an equal rate.
Excellent explanation Charlie. The syncho was definitely the missing piece to the puzzle!