Rear Differential Lock

I was testing out the rear differential lock system on my '19 TRD 4WD, having never used it. With the vehicle stopped and in neutral I switched to 4L and the 4LO light lit (along with a couple of others). I moved forward a few feet and stopped, back to N. I pushed the rear differential lock switch. The light flashed red and the orange ABS light lit (steady). I waited a while, it didn't stop flashing red so I shut off rear differential lock. I went out of 4LO. I tried the process 3X, and once it seemed to engage, i.e. the rear differential lock light went to steady red. Is there a reason engaging the rear differential lock is hit or miss? Or am I doing something wrong?

While I am at it, can someone please explain the difference between LSD and rear locker? The manual only tells how to activate. Also, I understand that Toyota rear locker uses the brakes, rather than clutches within the differential itself. Is that correct? it sounds more practical and cheaper in the long run.

 

In order for the locker to engage the axle shafts in both axles have to be lined up which make both axles turn at the same speed always, not to be used on hard surfaces, only very loose.

Next time push button when flashing put in gear and steer easy rite or left and creep forward till lite goes solid.

LSD=limited slip differential is now computer controlled, meaning open differential, when one rear tire slips the comp. will apply braking force to that wheel so power is directed to the tire that has traction.

08 down uses clutch packs inside the diff. to achieve the same action.

 

OK. Thanks Sparkystaco. So LSD is different than rear locker. Got it.

 

Yes, the biggest difference is the Locker is Locked all the time.
The tires spin all the time, at the same time.
There is no delay before the wheels are locked together.

LSD requires a wheel to spin before the differential “locks” the wheels together.
Technically it’s not locked together like a real locker. But for comparison purposes, we’ll go with this explanation.

If you really want to know the differences.
You could look up “Mechanical Locking Differential”
And “Brake Actuated Limited Slip”

You have the best of both world.

My truck is Locked, or it is not.
I have no type of LSD.
My truck is of course older.

 

Thanks for the education. Anyone know the type of locker Toyota uses? There are quite a few different designs available.

While I'm at it, this truck lacks A-TRAC but has CRAWL feature. I think with a rear locker and no A-TRAC the front differential is open. Does the CRAWL feature make up for lack of A-TRAC?

 

The Locker in the Tacoma is Electronically actuated.

There are primarily 3 types.
Mechanically, Electrically, and Air.



I am not sure on the CRAWL.
I’m not up on my 3rd Gen knowledge.
But I would guess, Yes.

I’d ask in the 3rd Gen section.

 

Crawl is another system that piggybacks on atrac. ATRAC is an electric brake booster that can create maximum braking force at idle vs the vacuum booster that requires rpm to generate boost.

The brake booster has individual solenoids for each wheel. When the abs sensor detects slip at a wheel ATRAC can brake that wheel with variable force without braking the other 3 wheels.

crawl is another layer of computer intelligence using that system

 

The e-locker in your truck is a solenoid that pushes a plunger that engages a dog clutch locking a side gear to the carrier. This turns your diff into a spool as both wheels are locked together and must spin the same speeds no matter what and therefore there is no differentiation. All selective lockers are this, either traditional open diff or locked into a spool. The method of actuation (air, electric, cable, etc.) is not relevant to the tractive performance.

To get your locker engaged you just need to get the dog clutch aligned and you can do this by driving forward and backward and turning slightly. There's no problem engaging the diff while moving mostly straight ahead though Toyota now limits you to under 5 mph for the engagement process.

An automatic locker is effectively a spool that allows some differentiation. It does this in a unique but simple way and this leads to some odd road manners but maintains spool level effectiveness.

An LSD only limits wheel slip and biases torque to some amount by creating resistance at the faster spinning wheel. It is limited in its effectiveness, especially compared to a locker, and different versions have vastly different torque biasing capabilities but they still allow for differentiation and good road manners. An LSD still requires some level of traction at the slipping wheel to have any effectiveness. Simulated limited slip is just a fancy term for modern traction control that applies selective braking to a wheel when it senses wheel spin. This type of slip control can easily be more effective at slow speeds and very low levels of traction than traditional LSD's.

MTS is the use of A-TRAC in the autos. It's just selective braking at slipping wheels to get more torque to the wheels with traction. Crawl control utilizes this traction aid while it tries to maintain a set forward speed. With the rear locked the MTS/A-TRAC will only operate across the front axle as the rear is locked and therefore there will be no slip across the rear axle to modulate.

Traction wise crawl control, A-TRAC, and MTS will never be as capable as a locker. The braking systems operate at a 50% bias ratio because they are braking across an open diff whereas a locker is capable of a 100% bias ratio. Having said that, anything that limits wheel slip is going outperform an open diff in offroad situations.

 

Well said