Auto LSD vs. Locking Rear Diff

To add:

The Auto LSD is operated via sensors, computer, & braking system.

The Locking rear diff is operated via switch that you manually turn on (or engage) and it literally locks the rear axleshafts together so they both spin at the same rate mechanically. The locking rear diff is not computer controlled. It's all mechanical.

The mechanical LSD (for the 05-08 crowd) is mechanically operated via the rear differential and is automatically working via torque/clutchpaks in the diff.
The mechancial LSD is not computer controlled.

 

I wish I had some LSD.

 

+1

 

I think people see "electronic" locking and think of witchcraft. The only thing electronic is the signal from the switch to the actuator on the diff. It's not pneumatic like an ARB or manual hub like an older truck.

 

Why am I limited to a speed of 5 MPH with the rear locker? Does one work better (limited slip vs rear locker) than the other?

 

The locker works much better for what it was designed for, you can go faster then 5mph if you do the grey wire mod so you don't have to be in 4lo.

 

To expand slightly. The rear, in normal operation, is an "open differential." Torque is transmitted to both rear wheels, but the amount of torque available is a result of the wheel with less traction. If you were stuck with one wheel spinning, it effectively has 'close to no torque,' therefore 'close to no torque' is transferred to the wheel with more grip. This doesn't help you get unstuck.

So, how could you go about transferring more torque to the wheel with grip? With a basic open differential, the only way would be to have that spinning wheel produce more torque. If there is no traction this can only be accomplished by applying the brake. With the 2009 trucks the brake is applied to the spinning wheel, which in turn allows more torque to be transferred to the wheel with more grip. That is what Toyota calls an "Auto LSD" and which is why it "incorporates the brakes."

All the controls are already in place via the ABS sensors, EBD system, and ESP...it is simply a programming change for Toyota to incorporate this.

Now as to why you can't exceed 5 mph with the mechanically locked differential, that is because both rear wheels are locked to the same speed. When "locked," for each revolution the right wheel does, the left does the same. When you turn a corner, inherently the outside wheel goes faster than the inside. When the diff. is locked, this is not possible...which will put greater demand on the rear axle train until wheel wheel spin/slipping is induced. Turing with both wheels going the same speed simply is not possible. Toyota apparently feels the drive train can withstand these forces at 5 mph + some safety factor. I wouldn't suggest trying a slalom course at 70 mph...I would expect to see parts of your drive train left all over the course.

The system is designed to get you unstuck. Once you have got out of the mud, switch it off because it is no longer needed.

 

^ good info, but I think you mean mechanical locker, not LSD. A mechanical LSD is designed to disengage around corners! I think the 5mph that Toyota designs into the system is for safety more then anything, your truck will handle very differently with the rear locked. Most drag cars have some sort of rear locker, lots are full spools, they run 150+mph. Another example would be pre-runners with the E-locker, they aren't speed limited to 5mph.

 

Yes, you are correct. I meant to use mechanically locked diff. Post edited.

 

got an 09 trd sport 4x4 was wondering what my rear diff will do will it lock in 4L or will i just have 3 wheels spinning what is the feelings to the auto lsd and vsc

 

sports dont have the rear locker option. you will get 2 wheels spinning, one front and one rear. if you apply the brakes slightly it will kinda give traction to both fronts though.

 

You will most likely have 3 wheels spinning, two rears and one front. The two rears because of the auto LSD. Although, I am not 100% sure if the auto LSD only applies to the rear...if it is for both front and rear, you will have all four spinning.

And Roy is correct, there is no lock on the Sport. You will be relying only on the auto LSD to brake the spinning wheel(s).

 

auto-lsd only works when engaged. it does not engage while in 4wd. I tested this theory out when offroading on some slippery rock. my buddy said only 1 front and 1 rear were spinning. when applying the brakes i got 2 fronts and only 1 rear to spin. kinda stupid imo.

 

Intersting. First off, I was assuming he would have turned it on. But I have a prerunner and am not farmiliar with 4wd operation. I just read the manual and it states the Auto LSD only works in 2wd mode. That would explain your results. Very odd Toyota would do it that way.

 

i agree. maybe they forgot they took the mechanical lsd out and doesnt work automatically in 4wd then. only works in 2wd

its ok, ill bet next year they fix it for the new models

 

It should only be a software change. The ABS module (to control the brakes) and sensors (to monitor for wheel slip) are all in place. They should do an update...it would take the dealer five minutes to flash your ECU.

Has anybody retrofitted the OE locker onto a sport?

 

yea, that would be nice. i asked them to set it up so i could turn the fogs on without the head lights and they had this deer in the headlight look.

 

after reading the replies on my question i got curious n found some mud this afternoon i got stuck in a lil muck the rear left n front right stayed spinning when pressing the brake i got a lil power power to the front left but not significant needless to say i was extremly disappointed i payed for a 4x4 not a 2wd which spins 1 in the front n 1 in the rear the stuff i tried to go thru was a jk my 2wd (rear 2wd) f150 went though the same spot and worse on 24'' rims with street tires i have also been having a lil trouble driving on a sand road when my tires begin to slightly slip the vsc kicks and the shut off only works to 30mph instead of helpin the stupid system throws me off some more its annoying any suggestion on how to fix these problems becaus i live deep in the woods but also drive alot on the highhway and in the city so i need a realistical solution not a straight axle honestly i love the truck but hate the way the rear n front dif work i think toyota messed up on this ystyn its inpractical for a 4wd

 

thats pretty typical of any 4wd system unless you have a locker.

 

I think most people need to understand how differentails work to understand Auto LSD/TRAC function. This video explains it really well. Just skip to 3:00 (the intro is kindda retarded.) TRAC/A-LSD/ATRAC works by breaking the spinning wheel.

http://www.youtube.com/watch?v=K4JhruinbWc