Question about A.D.D. System

[mtbtim]

I've got a question about the Automatic Differential Disconnect system. I know the CV axles are turning all the time because they are bolted to the wheel hubs, but, does that mean the ring and pinion are turning all the time as well? Since the front driveshaft doesn't turn until you put it in 4wd, I assumed the ring and pinion were not turning. One of the sites I found discussing this subject said the ring and pinion are turning all the time.

Can somebody also explain how the ADD system works to switch from 2wd to 4wd? What is actually happening in the differential to make the switch?

Thanks!

 

[spartacus]

I've got a question about the Automatic Differential Disconnect system. I know the CV axles are turning all the time because they are bolted to the wheel hubs, but, does that mean the ring and pinion are turning all the time as well? Since the front driveshaft doesn't turn until you put it in 4wd, I assumed the ring and pinion were not turning. One of the sites I found discussing this subject said the ring and pinion are turning all the time.

Can somebody also explain how the ADD system works to switch from 2wd to 4wd? What is actually happening in the differential to make the switch?

Thanks!

As I understand the ring and pinion rotate even when not engaged. I think it explains it fairly well here
https://www.off-road.com/trucks-4x4/tech/the-automatic-disconnecting-differential-system-19259.html

 

[spartacus]

this is for a hilux surf but explains it in detail.
https://www.toyotasurf.asn.au/techsite/add.htm

 

[JZiggy]

[MENTION=120071]mtbtim[/MENTION]

The ADD system disconnects the pass side stub shaft going into the differential. The pass side CV and stub shaft remain connected and spin on their own. The driver side CV is plugged into the differential carrier and so it at least makes the spider gear on that side spin. If you have an open diff then the "path of least resistance" is for the other spider gear to spin the opposite direction, keeping the ring & pinion from spinning at all.

 

[mtbtim]

As I understand the ring and pinion rotate even when not engaged. I think it explains it fairly well here
https://www.off-road.com/trucks-4x4/tech/the-automatic-disconnecting-differential-system-19259.html

That's the same site I found as well which left me confused. When I change the front differential oil, it looks brand new as opposed to the rear diff fluid that looks like it's broke down quite a bit after all the miles. If the front differential ring and pinion are turning all the time like the rear diff, you'd think the oil would look a little worse after 30k miles.

 

[mtbtim]

[MENTION=120071]mtbtim[/MENTION]

The ADD system disconnects the pass side stub shaft going into the differential. The pass side CV and stub shaft remain connected and spin on their own. The driver side CV is plugged into the differential carrier and so it at least makes the spider gear on that side spin. If you have an open diff then the "path of least resistance" is for the other spider gear to spin the opposite direction, keeping the ring & pinion from spinning at all.

Hey Jordan, so you're saying the ring and pinion doesn't spin in 2wd, correct? That website linked said the differential is turning all the time but maybe they just meant the spider gears and not the ring and pinion.

This makes more sense to me and why when I change the fluid it looks brand new.

 

[gamefreakgc]

Very interested in this since I have a sound in the front end I can't seem to diagnose and the dealer is just making stuff up. So the CV axles and part of the front diff is rotating under normal 2WD operation? Anything else?

 

[JZiggy]

Hey Jordan, so you're saying the ring and pinion doesn't spin in 2wd, correct? That website linked said the differential is turning all the time but maybe they just meant the spider gears and not the ring and pinion.

This makes more sense to me and why when I change the fluid it looks brand new.

If the ring & pinion are turning then the driveshaft has to be turning as well. It should be simple to verify if that's happening in 2WD mode.

 

[mtbtim]

If the ring & pinion are turning then the driveshaft has to be turning as well. It should be simple to verify if that's happening in 2WD mode.

Ok, this is the exactly what I was thinking as well. I know for a fact the front driveshaft doesn't turn in 2wd because I've looked under the rig while somebody drove very slowly next to me in 2wd. So, that article above should have been more specific what they meant when they said the differential is also turning in 2wd with an A.D.D. system.

 

[spartacus]

That's the same site I found as well which left me confused. When I change the front differential oil, it looks brand new as opposed to the rear diff fluid that looks like it's broke down quite a bit after all the miles. If the front differential ring and pinion are turning all the time like the rear diff, you'd think the oil would look a little worse after 30k miles.

I think as [MENTION=148218]JZiggy[/MENTION] explains. essentially because of counter rotation on opposite ends the ring and pinion remain stationary until the 4x4 is engaged which makes sense and so you would be right when it comes to differential oil looking clean.

 

[Tyler James Inc]

I agree with the conclusion the spider gears are the only thing spinning when in 2WD. What I think is crazy is how you can shift into 4WD on the fly(in the push button cases) when the front driveline isn't spinning, and the shafts are actually spinning in opposite directions at the ADD sleeve!

 

[JZiggy]

I agree with the conclusion the spider gears are the only thing spinning when in 2WD. What I think is crazy is how you can shift into 4WD on the fly(in the push button cases) when the front driveline isn't spinning, and the shafts are actually spinning in opposite directions at the ADD sleeve!

That's an interesting point. If you have manual hubs and the hubs are unlocked and you're moving forward in 2WD the shifter will crash if you try to push it into 4WD. Clearly this doesn't happen with the ADD systems.

Perhaps there is some way for the front prop shaft to accelerate while the system is shifting into 4WD?

Even if the ring & pinion are spinning it's not surprising that the oil would come out clean since they're running under zero load. I don't think clean oil verifies our "R&P don't spin" theory.

 

[TheDurk]

That's an interesting point. If you have manual hubs and the hubs are unlocked and you're moving forward in 2WD the shifter will crash if you try to push it into 4WD. Clearly this doesn't happen with the ADD systems.

Perhaps there is some way for the front prop shaft to accelerate while the system is shifting into 4WD?

Even if the ring & pinion are spinning it's not surprising that the oil would come out clean since they're running under zero load. I don't think clean oil verifies our "R&P don't spin" theory.

Well, wait a second. If the prop AND left wheel are both engaged first, then there should be a speed match when the sleeve engages the right stub shaft. The system just has to do the prop shaft first. The front prop shaft is tied to the rear wheels through the TC which are spinning at the same rate as the engaged front wheel, assuming straight line driving, of course.

Do I have this right? Diffs always confuse me....

 

[mtbtim]

That's an interesting point. If you have manual hubs and the hubs are unlocked and you're moving forward in 2WD the shifter will crash if you try to push it into 4WD. Clearly this doesn't happen with the ADD systems.

Perhaps there is some way for the front prop shaft to accelerate while the system is shifting into 4WD?

Even if the ring & pinion are spinning it's not surprising that the oil would come out clean since they're running under zero load. I don't think clean oil verifies our "R&P don't spin" theory.

Well, I know for a fact the front driveshaft does not turn in 2wd. So, how the hell is the ring and pinion turning with the driveshaft stationary?

 

[TheDurk]

Well, I know for a fact the front driveshaft does not turn in 2wd. So, how the hell is the ring and pinion turning with the driveshaft stationary?

They don't--only the two spiders and the left stub-shaft drive gears turn. The ring is attached to the right stub-shaft inboard of the disconnect and those stay still. The pinion too, obviously.

That's my point--once the pinion is engaged by the TC, THEN the pinion is turning, so does the ring, then so does the right side inboard half-shaft, the wheel is already turning, so it engages smooth. The right-side half shaft inboard piece does not move in 2WD.

 

[TheDurk]

I agree with the conclusion the spider gears are the only thing spinning when in 2WD. What I think is crazy is how you can shift into 4WD on the fly(in the push button cases) when the front driveline isn't spinning, and the shafts are actually spinning in opposite directions at the ADD sleeve!

Not opposite, the right inboard half shaft and side gear are stationary. It's just the carrier which is going backwards, with one side gear fixed and one side turning.

 

[spartacus]

Well, I know for a fact the front driveshaft does not turn in 2wd. So, how the hell is the ring and pinion turning with the driveshaft stationary?

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

 

[JZiggy]

Not opposite, the right inboard half shaft and side gear are stationary. It's just the carrier which is going backwards, with one side gear fixed and one side turning.

But the ring gear is bolted to the carrier, so if it's going backwards then the R&P and DS are spinning too.

Last time I messed around with an open diff I saw that if you spin one side gear forward and hold the carrier still then the other side gear spins opposite.

 

[mtbtim]

My head hurts. I find this confusing as all hell. That video [MENTION=50279]spartacus[/MENTION] linked was a helpful representation of what's happening but I'm still a little mystified.

 

[phattyduck]

My head hurts. I find this confusing as all hell. That video [MENTION=50279]spartacus[/MENTION] linked was a helpful representation of what's happening but I'm still a little mystified.

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