With the locking center differential and MTS/ATRAC, what is the use case for the locking rear differential? (1 Viewer)

[ryant]

I’m trying to understand the four-wheel-drive system of the Lexus GX 550. Since I’m a novice at this, this may be an ignorant question. But, I haven’t been able to find an answer.

Given the fact that the truck has a locking center differential and MTS, what is a use case for the locking rear differential?

 

[Mack]

It will cause less wear to your brakes in very traction limited environments. The MTS uses the brakes to transfer power to the wheel with traction.

 

[rangertrace]

I spent 3 days last week in Moab and I tried it both ways. I honestly couldn't tell you the difference. I went up and down some very difficult obstacles and it basically drove itself in crawl mode only came away with a couple minor dings.

 

[cmfhsu]

Caveat that I own a Lux+ and have no interest in off roading it, but here's my understanding of the benefits of a rear locker:

• Less shock load on the rear differential, theoretically increasing reliability and longevity
• More consistent, reliable traction, especially when one front wheel and one rear wheel are losing grip. I've seen videos of the GX struggling in some MTS modes in that scenario. If you're in a precarious place, you don't want to have to give it a bunch of gas and jiggle around while ATRAC sorts you out.
• It still works when you give it full throttle. I've found older versions of ATRAC struggle if you need momentum and wheel slip and high throttle openings to make it up a slippery hill - especially in extremely low grip scenarios like snow and ice. Will see how this gen ATRAC works this winter, I guess
• It still works if one of your wheel speed sensors dies - "it will always get you home", as people say
• It should give you a little more rotation & slide when turning in sand or loose surfaces (purely vehicle dynamics theory - not sure if this is proven in our cars), which should help with frustrating understeer in dunes and higher speed desert stuff

 

[Arewethereyet]

Thanks to the power of AI....

A locking rear differential forces the two rear wheels to spin at the same speed, improving off-road traction on a single axle. A locking center differential forces the front and rear axles to turn at the same speed, distributing power equally between both axles and converting an AWD vehicle into a 4WD system for better traction on all wheels.

Locking rear differential

• Purpose:
  To prevent one rear wheel from spinning while the other sits idle in low-traction situations.
  
  
• Function:
  It locks the right and left rear wheels together, so if one wheel loses traction, the other still receives power and pushes the vehicle forward.
  
  
• Use case:
  Ideal for situations where one rear wheel is on a slippery surface (like mud or ice) and the other is on solid ground.
  

Locking center differential

• Purpose:
  To provide a 50/50 power split between the front and rear axles in an all-wheel-drive or full-time 4WD vehicle.
  
  
• Function:
  It locks the front and rear axles together, forcing them to rotate at the same speed, which is useful when one axle starts to lose traction.
  
  
• Use case:
  Essential for off-road driving on surfaces like dirt, gravel, or snow, as it prevents the vehicle from getting stuck if all wheels on one axle lose grip.
  

Key difference

Feature	Locking Rear Differential	Locking Center Differential
Function	Locks the wheels on the rear axle together.	Locks the front and rear axles together.
Effect	Distributes power between the two rear wheels.	Distributes power between the front and rear axles.
Primary benefit	Improves traction on the rear axle.	Turns an AWD system into a 4WD system, improving overall traction.

 

[Arewethereyet]

As I understand it the lock diffs are mechanical while Atrac is electronic. I ran Red Cone and Radical Hill on stock wheels and suspension in Colorado a few weeks ago primarily using Atrac/Crawl control finding it much better on off camber obstacles particularly when flexing the suspension to the point two of the four tires were off the ground. I could see using the locking rear diff if I need to place power to the non slipping tire focusing power on the rear axle while the center diff would serve if negotiating deep snow or mud. The A trac is a competitive advantage for these vehicles off road.

 

[AtomicEric]

In very slow speed rock situations the rear left and right tired turn at the same speed without any delay, especially in low to "NO" speed maneuvers when any slippage could be an issue. Slow rock work when maximum flex is exceeded the rear lock can be better than the automatic control with breaking. A few videos reviews are noting the system is now very very good and the Delta between wanting the rear locker on or allowing automation to take over.

So you are likely correct noting it was not needed, but it can be a preference to many who have used them in the past.

In general I only activate during some short slow technical trail work then turn off while driving normal terrain as when it is engaged the locker induces slip during turning. In these cases the track controls do a much better job. This is also true in snowy driving. Better to let the track controls do the work to minimize braking the tires free.

A rear locker engaged on the road in snow quickly gets both rear wheels to brake free in turns which (although fun at times) can land you in a ditch.

 

[rangertrace]

What mode disengages the sway bars?

 

[AtomicEric]

I think the rock would let both go, but it may need to be put into a flex situation vs just being connected or not. I also read that the dirt mode in MTS disconnects the rear. That word very well for me.

 

[rangertrace]

From what I read today the EKDSS locks/unlocks the sway bars as need with driving conditions.