Yes to eLSD or No to eLSD on our next Expedition

[Anerbe]

I tried to so a simple test in 2WD mode going uphill on my driveway, with one side off onto the ice covered grass, other side on dry pavement.

I tried the following combinations trying with both locked rear active and deactivated:
- Full Stability On
- ESC off (single brief press on ESC)
- Advance Trac Off (long hold on ESC)
All 3 were done in "Normal" drive mode

In all 3 settings above I didn't notice any difference: all 3 were the same results for the two settings below.
- Locker on - zero slip - went up like the whole vehicle was on dry.
- Locker off - very minor slip, then a light bucking of the rear, then went up driveway without further slip.

My understanding is that ELSD runs independent of the stability system, and in itself monitors slip and readjusts power to the tractive side automatically. I don't think you can deactivate the system to run the rear like an open differential. It's always active it seems.

Now, perhaps the shift of power becomes more or less immediate in different drive modes, but my intent was to determine if you can essentially run the rear as an open diff, which I don't believe is possible.

 

[LokiWolf]

I tried to so a simple test in 2WD mode going uphill on my driveway, with one side off onto the ice covered grass, other side on dry pavement.

I tried the following combinations trying with both locked rear active and deactivated:
- Full Stability On
- ESC off (single brief press on ESC)
- Advance Trac Off (long hold on ESC)
All 3 were done in "Normal" drive mode

In all 3 settings above I didn't notice any difference: all 3 were the same results for the two settings below.
- Locker on - zero slip - went up like the whole vehicle was on dry.
- Locker off - very minor slip, then a light bucking of the rear, then went up driveway without further slip.

My understanding is that ELSD runs independent of the stability system, and in itself monitors slip and readjusts power to the tractive side automatically. I don't think you can deactivate the system to run the rear like an open differential. It's always active it seems.

Now, perhaps the shift of power becomes more or less immediate in different drive modes, but my intent was to determine if you can essentially run the rear as an open diff, which I don't believe is possible.

Awesome Test!

 

[Anerbe]

I'll do any thing for science (engineer) - has a similar experience with my RWD C63S with ELSD as the Expedition w/o locked diff a few days later ( more responsive vs. button off, but clearly not immediate like locked). the system is like in the AMG-GTS, where it can torque vector on top (overdrive the outer wheel, not necessarily equal 50/500. my neighbor thought i was crazy driving half of it on the snow and going up and down my driveway.

My prior M3 had a diff lock, which was clutch based, and differential of wheel speed caused increase of fluid pressure from a pump to actuate. It was a bit slower to actuate, as it had to build up pressure to progressively lock, but it could lock 100% if the variation in wheel speed was still present.

 

[Fastcar]

Yes. Far better to have it and not need it than need it and not have it. You did say "mud", "snow" and "ice" which are exactly where you'll want it.

Truly written! I couldn't agree more!!

 

[LokiWolf]

I'll do any thing for science (engineer) - has a similar experience with my RWD C63S with ELSD as the Expedition w/o locked diff a few days later ( more responsive vs. button off, but clearly not immediate like locked). the system is like in the AMG-GTS, where it can torque vector on top (overdrive the outer wheel, not necessarily equal 50/500. my neighbor thought i was crazy driving half of it on the snow and going up and down my driveway.

My prior M3 had a diff lock, which was clutch based, and differential of wheel speed caused increase of fluid pressure from a pump to actuate. It was a bit slower to actuate, as it had to build up pressure to progressively lock, but it could lock 100% if the variation in wheel speed was still present.

Only clarity I would offer, is these are not truly locked. It is not a pin based system like the 150. The ELSD uses clutches to simulate lock, but it has been proven they can slip, and can get hot because of it. I personally believe the ELSD vs ELD is better in everything except extreme conditions, or off road. Where most people use Expeditions, ELSD and its ability to modulate is better.

 

[Anerbe]

Only clarity I would offer, is these are not truly locked. It is not a pin based system like the 150. The ELSD uses clutches to simulate lock, but it has been proven they can slip, and can get hot because of it. I personally believe the ELSD vs ELD is better in everything except extreme conditions, or off road. Where most people use Expeditions, ELSD and its ability to modulate is better.

I agree with you that the failure risks are greater with a clutch based system, but if the ELSD was designed to send 100% power to one side, it has the same power distribution as a locker. Fully engaging a clutch that is designed not to slip equals an actuated gear lock - I draw similarities to a manual transmission. If the clutch is fully engaged, it is transferring 100% power as locked, unless it's operating outside of its design intent, causing slip.

I see you view on why you see any clutch based system not a true locker, but your definition of locker then requires all the positives of a gear based activation. I see a locker as the ability to send all power to a side with traction, simply that. Both clutch and gear activation have their pros and cons.

 

[duneslider]

Due to the fact that it is a clutch and doesn't have an actual physical pin does mean that at some point torque could overwhelm the friction disc's ability to hold. Most probably won't every have issues with this. I believe Jeep used a similar style "locker" in the grand cherokee and commander for a handful of years and it was generally regarded very well and people really liked it. I don't know how similar they are but they way they work is similar.

I also suspect that the friction discs can wear out and not work at all.

I haven't looked but do these eLSD's require a special friction modifier in the fluid like the chrysler products did?

 

[LokiWolf]

I agree with you that the failure risks are greater with a clutch based system, but if the ELSD was designed to send 100% power to one side, it has the same power distribution as a locker. Fully engaging a clutch that is designed not to slip equals an actuated gear lock - I draw similarities to a manual transmission. If the clutch is fully engaged, it is transferring 100% power as locked, unless it's operating outside of its design intent, causing slip.

I see you view on why you see any clutch based system not a true locker, but your definition of locker then requires all the positives of a gear based activation. I see a locker as the ability to send all power to a side with traction, simply that. Both clutch and gear activation have their pros and cons.

In Ford's ELD(Electronic Locking Differential - F150) an actuator moves a pin, "Locking" both left and right into spinning at the exact same speed. So 50/50 technically. This chatters while turning on any but very slippery conditions. It is locked hard.

In Ford's ELSD(Electronic Limited Slid Differential) - I am sure you already know and some others do to, but for the sake of others, Clutch based LSD's use springs in the Mechanical assembly to provide preload, and depend on the slight movement because of increased increased torque of the spinning wheel, therefore causing the opposing clutch pack to engage, sending power to the wheel with traction. The ELSD does this electronically using actuators. Those actuators provide the force to engage the clutches. In some extreme cases the force trying to be overcome on that side exceeds the holding force of that actuator, and slippage occurs, and the system will disengage the ELSD. Putting it in "Locker" mode helps to prevent this by applying maximum force to send to both sides.

Under most conditions the ELSD is a FAR better option, because of its ability to vary torque between the wheels. Our ELSD is a Limited slip differential, that can be forced to think wheels are spinning even before they are, Lock Mode. That is why your test showed that had less spin before you started moving.

 

[duneslider]

...and this is why I went with air lockers on my 2000 EB.

They work great too, until they don't. I have air lockers in my jeep and on more than one occasion they have stopped working. I keep an air line repair kit in my offroad kit. I currently have a leak some place that I need to track down. I probably should just run all new lines after this many years. They do lock solid when they do lock though.

 

[JExpedition07]

I agree with you that the failure risks are greater with a clutch based system, but if the ELSD was designed to send 100% power to one side, it has the same power distribution as a locker. Fully engaging a clutch that is designed not to slip equals an actuated gear lock - I draw similarities to a manual transmission. If the clutch is fully engaged, it is transferring 100% power as locked, unless it's operating outside of its design intent, causing slip.

I see you view on why you see any clutch based system not a true locker, but your definition of locker then requires all the positives of a gear based activation. I see a locker as the ability to send all power to a side with traction, simply that. Both clutch and gear activation have their pros and cons.

If you really put the truck into a demanding situation with wild wheel articulation the lsd gives way pretty fast, a locker won’t. But for most of what we do an lsd is safer and better. Off road a lot and the locker is better. I will say in most situations where your wheels are articulated that much the lsd give way—one locker probably isn’t going to cut it anyway.