How does 4x4 system work on Gen III? (Full Version)

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How does 4x4 system work on Gen III?

  

tj90 -> How does 4x4 system work on Gen III? (10/9/2006 7:50:39 PM)

OK - Im trying to understand the function of the super selector on the '01 montero / pajero and newer. There are 4 drive positions - 2wd, all wheel drive, 4wd high, 4wd low. The 4wd position is easy to understand - the transfer case distributes power to all 4 wheels with gears. All 4 wheels rotate at the same rate. Transmission must be in neutral and stopped to activate 4wd system. I assume this is the case since gears in the transfer case are engaging and disengaging. Please confirm my understanding....

I dont understand the all wheel drive system. Power is split - I believe 40/60% F/R power distribution - please confirm. The super selector switch shows the transfer case light off. Transfering from 2wd to AWD can be done at speeds below 60 mph and in any gear. How does this work? Is it a viscous coupling in the transfer case? Is the front propellor shaft always moving, regardless of shift position? What is actually happening when you go to AWD? How does the power get split?

Im assuming that both front and rear differentials are open design (no LSD or clutch packs). Does the montero ECU automatically applies breaks to the spinning wheel to prevent the entire axle from loosing traction if one is being lost....

BTW, I replaced the Mobil 1 gear oil in the transfer case and differentials with specialty formulations MTL-R in the transfer case and SP HDS GL-5 in the differentials. I have noticed that shifting in the transfer case(?) seems quieter. The Mobil1 shifts was audible - now shifts are barely audible... Maybe its placebo, but I like it so much that Im changing to MTL-R for my manual tranny on my other car.

  
Manybrews -> RE: How does 4x4 system work on Gen III? (10/10/2006 7:15:29 PM)

there is in fact a viscous coupling in the center differential. and most (if not all) monteros have a limited slip differential in the rear (unless you have a locking diff... some countries offer different things).
basically when you're in AWD, the power goes where its needed most, but still allows differentiation of the wheel speeds as conditions call for it (cornering on pavement, etc).
if you're in deep sand or snow, switching to 4wd locks the center differential solid, not allowing for differentiation, giving exactly a 50/50 power split between front and rear.
as far as the actual switching goes, the transfer case is both electronic and equipped with a large synchronizer assembly. when you move the lever, you're only moving a switch. There is an electronic actuator on the transfer case that moves a shift fork. That shift fork spins the synchronizer up to speed (and thus the driveshaft leading to the front axle).
when its up to speed, the front axle disconnect engages, giving you AWD (or 4WD, depending on what you selected).

its basically bulletproof. The only issues ever encountered involve corrosion on one or more of the 5 switches on top of the transfer case. it needs those switches to identify what mode its currently in. If one fails, the system usually defaults to AWD and makes the dashboard indicator flash.
you can freely switch between 2WD, AWD, and 4WD at any speed up to 60 MPH. switching to 4WD low requires stopping the truck.

keep in mind this is ONLY FOR the super select AWD system. Some cheaper monteros had an old fashioned 2WD/4WD/4WDlow transfer case that was 100 percent manually activated. Basically, it was the same driveline as the montero sport.

there werent a lot of those on the market, but they are present. any 01 and newer montero with a 4 speed auto has the old fashioned transfer case. Any 01 and newer with the 5 speed auto has the super select AWD system (which is most monteros).

tj90 -> RE: How does 4x4 system work on Gen III? (10/10/2006 9:06:57 PM)

Manybrews: Thanks for the information! A few questions on your post.

Im assuming that since the rear axle is LSD design, the front is an open differential. If you are in 4wd mode or AWD, power going to front axle would be lost if one wheel gets into the air or hits ice. I have been 4wheeling and when a wheel looses traction, the indicator on the dash blinks that particular wheel. Somehow, the ECU is detecting the wheel slippage and indicates this on the wheel - there must be speed sensors on each wheel (I can see a splined ring near the outer CV joint is for this purpose I think....)

Anyway, does the ECU send a signal to the ABS system to "stop" the spinning wheel to insure that power transmits to the other wheel on the front or rear axle? I would assume this would be more problematic for the front since its not(?) LSD....

Good to know that the front propellor shaft is not always rotating in 2wd more. I see some electrical wires going to the front axle so I did not know if it was a sensor or it was actually actuating a hub lock or something.

One time I was 4wheeling in mud and got all 4 wheels stuck in the mud. I knew I was screwed when I look down on the dash and all 4 wheels were blinking. How the heck did the montero know that I lost traction on all 4 wheels?! Especially if all wheels were rotating at the same rate!?

On raining days when its safe, I purposely put the truck into a slide to see the traction control system kick in. The power transmission system of the GEN3 is amazing for driving in adverse conditions.


Winshawn -> RE: How does 4x4 system work on Gen III? (10/12/2006 2:25:43 PM)

The Active Traction and Skid Control system (ATSC) was added for the '03 models. It was not present on the '01 and '02 models. The '03 and up Montero's have open differentials both front and rear. The ATSC monitor's a variety of things and then can modulate the braking on individual wheels and/or modulate the accelerator since it is "drive by wire."

The front wheel hubs are always engaged. Only the Gen 1 hubs actually dissengaged the wheel from the front drive shaft. The Gen II hubs were always engaged too.

There is a vacuum actuated clutch incoporated into the front differential that engages the front driveshafts to the differential gears.

So, for '03 on it is a completely "open" 4 wheel drive system aided by electronic brake and throttle activation to help prevent wheel spin and vehicle control.

I too have tried to spin the back end of the truck while in the rain and making a sharp right or left turn. It just cannot be done.

Another time I noticed the ATSC system taking over was when I was manuevering on a steep snowy driveway. I was backing up and making a turn and as a wheel would start to spin I could feel the brakes being applied to individual wheels and the indicator light on the dash would light up. It was pretty cool.


tj90 -> RE: How does 4x4 system work on Gen III? (10/12/2006 2:55:56 PM)

Winshawn you said: There is a vacuum actuated clutch incoporated into the front differential that engages the front driveshafts to the differential gears.

Are the front driveshafts = half axles?

It sounds like the following (for 03 and newer):
2wd mode: transfer case rotates both propellor shafts thru viscous coupling. Power going to rear open diff. Power lost to either rear wheel and ATSC kicks in and transfers more power to wheel with traction. Power going to front differential just spins differentials - since front half axle clutches disengaged, no power to front wheels.
AWD mode: Power thru all wheels. Clutches engage on front half axles. Same transfer case settings as 2wd mode. ATSC still active but now ATSC will insure power not lost to front wheels by using brakes to transfer to power from slipping wheel to the other with traction.
4wh mode: Transfer case shifts so that now gear is splitting power to 50/50 F/R. ATSC active.
4wl mode: Another lower gear in transfer case for more torque. ATSC not active. Wheel spins - your screwed. Indicator wheel lights but ECU drive by wire system does not try to compensate.

I guess I can see why ATSC would not be active in 4wd low setting, cause you dont need the ECU to outthink your power requirements - especially in hairy situations. Maybe the ATSC system is "deactivated" according to the dash, but in reality the brakes are still active - since its so handy with open differentials.

Is this right? Sorry to beat a dead horse, but Im an engineer and I get paid to be detailed (or OCD depending on your perspective).

Im curiuos why ATSC is deactivated in 4wd low mode. I would think that you would loose the brake activation and spin control feature and be purely dependent on the open differential on both axles. This would be bad if you lost traction on one wheel of each axle. I would think that ATSC would be a great feature even when 4wd low mode to effectively get a thorson differential = > power to other wheels if one or more loose traction.

Winshawn -> RE: How does 4x4 system work on Gen III? (10/12/2006 4:04:23 PM)

Crap I typed a full answer and then accidentally deleted it.

The FSM has a little table that describes when the ATSC functions are active. There are two functions "Brake Control" and "Engine Control". The Brake control is alwas active, even in 4LLC. The Engine control is only active in 2H and 4H. It is off under all other conditions. One other thing to note, the Brake Control is active even when you turn off the ATSC with the console switch.

In 2WD mode the transfer case only powers the rear propellor shaft.

tj90 -> RE: How does 4x4 system work on Gen III? (10/12/2006 4:45:10 PM)

If the front propellor shaft does not rotate in 2wd mode, then what is the purpose of the vacuum actuated clutches on the front half axles? I dont see their purpose if the xfer case is distributing the power in all modes.

Thanks for confirming the actual function of the ATSC. Even when off, brake control of spinning wheels is VERY important! Engine control should be on in AWD mode. Dont you think?

Winshawn -> RE: How does 4x4 system work on Gen III? (10/12/2006 9:35:44 PM)

I consider 4H as the AWD mode. In that mode engine control is active.

If you did not have the freewheel clutch, the propeller shaft would rotate in 2H mode. So, in 2H mode the front differential does not rotate and the front propeller shaft does not rotate. It save a little hp. However, the front half axles rotate which wastes a little power.

Manybrews -> RE: How does 4x4 system work on Gen III? (10/13/2006 6:21:28 PM)

quote:



It sounds like the following (for 03 and newer):
2wd mode: transfer case rotates both propellor shafts thru viscous coupling. Power going to rear open diff. Power lost to either rear wheel and ATSC kicks in and transfers more power to wheel with traction. Power going to front differential just spins differentials - since front half axle clutches disengaged, no power to front wheels.


not correct. the front driveshaft is not turning. The transfer case is only delivering power to the rear driveshaft. the viscous coupling is not doing anything in 2WD.
quote:


AWD mode: Power thru all wheels. Clutches engage on front half axles. Same transfer case settings as 2wd mode. ATSC still active but now ATSC will insure power not lost to front wheels by using brakes to transfer to power from slipping wheel to the other with traction.

basically correct but for the transfer case part. The front driveshaft is now engages, and the viscous coupling is trying to transfer equal power to the front and rear (but will allow for differentiation when needed).
quote:


4wh mode: Transfer case shifts so that now gear is splitting power to 50/50 F/R. ATSC active.
4wl mode: Another lower gear in transfer case for more torque. ATSC not active. Wheel spins - your screwed. Indicator wheel lights but ECU drive by wire system does not try to compensate.

pretty much correct.

quote:


I guess I can see why ATSC would not be active in 4wd low setting, cause you dont need the ECU to outthink your power requirements - especially in hairy situations. Maybe the ATSC system is "deactivated" according to the dash, but in reality the brakes are still active - since its so handy with open differentials.

Is this right? Sorry to beat a dead horse, but Im an engineer and I get paid to be detailed (or OCD depending on your perspective).

in 4WD low, you should also have a speed limiter, and the truck should not shift into overdrive.
quote:


Im curiuos why ATSC is deactivated in 4wd low mode. I would think that you would loose the brake activation and spin control feature and be purely dependent on the open differential on both axles. This would be bad if you lost traction on one wheel of each axle. I would think that ATSC would be a great feature even when 4wd low mode to effectively get a thorson differential = > power to other wheels if one or more loose traction.

theyre assuming ultra-low speed trails and such if you're using 4WD low.. traction control/ABS has proven itself unreliable in such situations, often causing issues you dont wish. A lot of off road situations are helped by the use of wheel spin, etc. Also, extreem angles (such as rock climbing) can often fool the systems.
they are best left off in such situations.

carlover626 -> RE: How does 4x4 system work on Gen III? (2/2/2007 12:14:40 PM)

What can I do if my AWD stick is not moving?
I attempted to switch to 4 high this morning and the stick moved from AWD a bit but the light is not on...now I cannot move the stick at all either to AWD / 4H / or 4L.

Any insight?

  

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