I know, another Locker vs anti spin Diff question

[Arterius2]

The locker, clutch LSD, and helical differential are all proactive. The helical gears that drive the outputs use torque and axial thrust to generate locking action to bind the wheels together. This is why it's always proportional to the weakest wheels available traction as it needs that torque to generate its locking force. The clutch based LSD applies pressure to the outputs which forces the greater traction wheel to receive torque proportional to the clutch pack pressure. The BLD system is reactionary but should compliment the helical differential nicely as it will magnify the braking affect. The only reactionary LSD I've seen is the Eaton G80 locking differential which requires a spun weight to lock against a mechanism that forces a wave gear to apply immense pressure to a clutch pack.



The difference is that a locking differential is able to bias more toque to the wheels with the most grip while the anti-spin differential will be limited. I'm assuming the trac-lok is a clutch based unit as there are clutch rebuild kits for the JL Trac-lok. This means your wheel with the most traction will always receive at least a minimal amount of torque proportional to the clutch packs force plus whatever torque the lower traction wheel can generate. In extreme situations it simply won't be able to drive the greater traction wheel without the BLD system which is reactionary.

Think of an open differential as a water hose with a T-fitting. If you plug one end up the water will flow to the opposite hole but will still transmit its force to your thumb plugging it. Even though the water isn't flowing it's still applying a force.

It's also important to note that an open differential varies the wheel's speed in relation to the carrier. With a stalled wheel the opposite wheel will spin 2x as fast as the carrier is rotated. As the slower spinning wheel spins closer to the carrier's speed so will the opposite wheel. If the carrier is stalled then one wheel spinning 100rpm forward will force the opposite wheel to spin 100rpm reverse. Spin the carrier at 100 rpm and now the reverse wheel is not rotating and the forward wheel is spinning at 200rpm, but both are still spinning 100rpm relative to the carrier in opposite directions.



You have it backwards, a locker biases torque from 0-100%, a helical diff will bias torque based off its TBR (for example a TBR of 3:1 can bias torque 75/25), and an open differential is always 50/50. It's really easy to understand. Lift a wheel off the ground and it cannot generate torque, so the opposite wheel with traction gets the same torque which is nothing. A locker will send 100% of torque to the wheel on the ground since the airborne one simply cannot generate any. A helical diff would act as open sending nothing to the grounded tire as 3 multiplied by 0 is 0.

Which makes the video you posted patently wrong. Also, torque and power are not the same. A stalled wheel receiving torque does not transfer power, so while an open differential biases torque 50/50 always the power flow is can vary wildly. Opposite with a locker, a spinning wheel that receives no torque is not transferring any power, and its power bias varies wildly as well.

I think you and @Stormin’ Moorman are mixing up AWD with 4WD.

An open front+rear diff in 4WD is still 50/50 front and back. But think of it having a centre diff locker because the drive shaft is basically a solid mechanical connection.

Even if the front wheels are spinning. You will still get 50% traction in the rear, because front and rear are locked solid.

What you were describing is AWD like a Subaru, not 4WD. There is a difference, AWD is like an open centre diff. 4WD is like a locked center diff.

In AWD, if one wheel spins, you get 0% power to all wheels.

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[OffroadCalling77]

Old thread but lots of good information here. Just out of curiosity. The system find on the 392. Since there is no longer a 2H by default, is this a true AWD like a Subaru or is it still 4WD hybrid?

 

[Arterius2]

Old thread but lots of good information here. Just out of curiosity. The system find on the 392. Since there is no longer a 2H by default, is this a true AWD like a Subaru or is it still 4WD hybrid?

It's 4WD.
Because while in 4-auto, the transfer case uses a clutch pack to bias torque from 40/60 to approximate 0/100 depending on wheel slippage.

It will drive normally in 40/60 split, but if one wheel slips completely, it will lock the clutch pack and send 100% power to the front/rear wheels and vice versa. Amount of power sent to the front/rear depends on the amount of wheel slippage. Think of it as AWD with a centre locker.

Here is a good video that explains how Selec Trac II works:
It basically switches between 2wd and 4wd and any varied range in between.

 

[OffroadCalling77]

It's 4WD.
Because while in 4-auto, the transfer case uses a clutch pack to bias torque from 40/60 to approximate 0/100 depending on wheel slippage.

It will drive normally in 40/60 split, but if one wheel slips completely, it will lock the clutch pack and send 100% power to the front/rear wheels and vice versa. Amount of power sent to the front/rear depends on the amount of wheel slippage. Think of it as AWD with a centre locker.

Here is a good video that explains how Selec Trac II works:
It basically switches between 2wd and 4wd and any varied range in between.

Thanks for sending that video over. Makes perfect sense. So with 4WD Auto as the default setting on the 392 is it always driving around with a 42/58 split at all times since there is no longer a 2H dedicated mode? I wonder if the 2022 model year Wranglers will be shipping with 4WD auto as default? Looking to buy a 2022 Rubicon.

 

[Arterius2]

Thanks for sending that video over. Makes perfect sense. So with 4WD Auto as the default setting on the 392 is it always driving around with a 42/58 split at all times since there is no longer a 2H dedicated mode?

Yes, that is right

 

[Arterius2]

I wonder if the 2022 model year Wranglers will be shipping with 4WD auto as default? Looking to buy a 2022 Rubicon.

I don't think they would remove 2WD from any non-392 Rubicons any time soon. As 2H has better fuel economy so lower CAFE numbers.

I think 392 is forced into full-time 4WD due to drive-train limitations. Which is not an issue with other engine options.

 

[OffroadCalling77]

I don't think they would remove 2WD from any non-392 Rubicons any time soon. As 2H has better fuel economy so lower CAFE numbers.

I think 392 is forced into full-time 4WD due to drive-train limitations. Which is not an issue with other engine options.

Got it. What do you think when ordering Selec-trac option for $595 on the 2022 models. Do you think it will still have the 2H option on there or come with only 4WD Auto?

 

[Arterius2]

Got it. What do you think when ordering Selec-trac option for $595 on the 2022 models. Do you think it will still have the 2H option on there or come with only 4WD Auto?

I personally ordered the Selec-Trac on my Sahara so I may be biased here.
I also use the selec-trac extensively during winter since I live north of the border and I do a lot of mountain driving.

If it were me, yes I will order the selec-trac again, even on a Rubicon. Pretty sure 2022 models will still have this option.

 

[wibornz]

On the Rubicon, the Jeep uses brakes to send traction to the other wheel. This has caused us problems a couple of times in different situations. We climb up Red Cone pass in Colorado with out the lockers on. We were about 3/4 of the way up to the pass, on two of the JLURs had overheated the rear brakes to the point they were sticking. It also caused one of the JLURs to go into limp mode. We also had one JLUR overheat the rear brakes in MOAB. Mind you it was already hot, but the rear brakes got so hot that the brakes were sticking. It took 9 water bottles to cool off the rear brakes and about a 1/2 hours of sitting before the JLUR wanted to come out of limp mode. At least laying on the flat rocks up on Golden Rim trail was relatively dirt free and we had plenty of cold water in the fridge. Use a knife poke a hole in the top and spray away.

Also running on the sand will cause the brakes to put on a heck of a work out sending traction to different wheels. I bet my Jeep will apply the brakes a thousand times in an hour while running around the Silver Lake Sand Dunes.

To give you an idea of how often the brakes in the rear were used by Jeep to transfer power around to the wheel with traction, I got about 24,000 miles out of the rear pads before I had to change them. I usually see north of 75,000 miles on vehicles before rear pads are needed. So now if I am in a limited traction area, like sand or know that the Jeep will be seeking traction a lot due to the terrain, I turn on the rear locker. This philosophy has made a huge impact on rear brake longevity. I am currently at almost 49,000 miles and my rear brakes are still in very good condition.

 

[aldo98229]

I personally ordered the Selec-Trac on my Sahara so I may be biased here.
I also use the selec-trac extensively during winter since I live north of the border and I do a lot of mountain driving.

If it were me, yes I will order the selec-trac again, even on a Rubicon. Pretty sure 2022 models will still have this option.

Luv the new pic!

 

[aldo98229]

Got it. What do you think when ordering Selec-trac option for $595 on the 2022 models. Do you think it will still have the 2H option on there or come with only 4WD Auto?

$600 for Selec-Trac is the biggest bargain on JL’s option list, IMO.

In Auto mode, the Jeep drives in RWD unless it detects slip in the front, at which point it engages the front axle. The whole procedure is instant and seamless.

I doubt Jeep would change Selec-Trac’s operation for 2022.

Yes, 392 appears to be in Auto mode all the time. I don’t know if it works like normal Selec-Trac or if it always in 4WD. Like @Arterius2 suggests, it likely has to do with reducing stress on the drivetrain.

 

[Firestarter]

I am not confusing AWD with 4WD. You CANNOT impart torque onto something without it having an opposing force. Just screw something into you drywall until it strips. You'll feel it develop more torque until it cannot. Same for the wheels

Open differentials are 50/50. If one wheel cannot generate any torque, then the other wheel cannot generate torque as well. A locker is 0-100% bias, including the center diff lock (or lack there of in part-time 4wd), and does not need the opposing wheel to generate torque for it to generate torque.

Further proof, a TORSEN uses helical gears to create a locking force within the differential. It is proportional to the input torque on the gears which requires traction to generate. They are referred to as torque biasing differentials because they bias 3x the torque the weakest wheel can generate to the opposite wheel (with a TBR of 3:1). A locker is far better at biasing torque than a torsen.

From auburn gear: "Torque bias, measured in lbs-ft, is the ability of the limited slip differential to divide the input torque unequally, allowing more torque to be delivered to the wheel with the most traction. Bias torque translates to more driving force, hence more horsepower to the ground. Torque bias is the measuring stick by which all limited slip differentials are compared."

Here's an example with one wheel developing 10 lbs-ft and the other 100 lbs-ft. Open differential both wheels develop 10 lbs-ft each for total axle torque of 20 lbs-ft. Torsen 3:1 TBR differential has one wheel develop 10 lbs-ft and the other gets 30 lbs-ft for a total of 40 lbs-ft of axle torque. A locked differential will develop 10 lbs-ft in the weakest wheel and the other will get 100 lbs-ft for a total axle torque of 110 lbs-ft.

If a wheel is not on the ground, how could it possibly develop or transfer torque?

EDIT: I added another source

From eaton: "Locking differentials (generically referred to as “lockers”) can lock the axles together to provide 100% of available torque to the wheel with traction."
https://www.eaton.com/us/en-us/products/differentials-traction-control/locking-differentials.html
This is why locking differentials are so much better than anything else. 100% of engine torque can be delivered to 1 wheel in a fully locked driveline.
Yes, it's a popular colloquialism to say locked differentials or part time transfer cases are 50/50. But they are not. Simply because it's a common phrase doesn't make it true. AWD is 25/25/25/25 (50/50 split at each differential) because if one wheel develops 0 torque then the differential develops 0 torque then the other axle develops no torque and all the other wheels develop 0 torque. Something like the STi uses a helical center diff with a 2:1 TBR (66/33 split) which CAN bias up to 66% of available torque to the strongest differential.


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Interesting... I did not know that.

As a side note, I wish Jeep would quit naming their 4wd systems and give real descriptions of what the products actually are. It's ridiculous that there is a Wikipedia page this long dedicated to the variations. Even Jeep's description leaves me with questions:

I think you and @Stormin’ Moorman are mixing up AWD with 4WD.

An open front+rear diff in 4WD is still 50/50 front and back. But think of it having a centre diff locker because the drive shaft is basically a solid mechanical connection.

Even if the front wheels are spinning. You will still get 50% traction in the rear, because front and rear are locked solid.

What you were describing is AWD like a Subaru, not 4WD. There is a difference, AWD is like an open centre diff. 4WD is like a locked center diff.

In AWD, if one wheel spins, you get 0% power to all wheels.

 

[Firestarter]

If you have a rubicon then you should really use the locking differentials.

Open differentials are always 50/50 split torque. So when one wheel cannot generate much torque the opposite wheel is limited to that. What BLD does is increase the torque that wheel can generate via the brakes to raise the amount of torque the stronger traction wheel can get.

With a locker, it just sends torque unequally to which ever wheel has the most traction. If both have equal traction and rpm demand then it will split torque equally.

The lockers also make it so the driveline torque is much lower than the BLD system because there is no need to impart torque into the brake.

On the Rubicon, the Jeep uses brakes to send traction to the other wheel. This has caused us problems a couple of times in different situations. We climb up Red Cone pass in Colorado with out the lockers on. We were about 3/4 of the way up to the pass, on two of the JLURs had overheated the rear brakes to the point they were sticking. It also caused one of the JLURs to go into limp mode. We also had one JLUR overheat the rear brakes in MOAB. Mind you it was already hot, but the rear brakes got so hot that the brakes were sticking. It took 9 water bottles to cool off the rear brakes and about a 1/2 hours of sitting before the JLUR wanted to come out of limp mode. At least laying on the flat rocks up on Golden Rim trail was relatively dirt free and we had plenty of cold water in the fridge. Use a knife poke a hole in the top and spray away.

Also running on the sand will cause the brakes to put on a heck of a work out sending traction to different wheels. I bet my Jeep will apply the brakes a thousand times in an hour while running around the Silver Lake Sand Dunes.

To give you an idea of how often the brakes in the rear were used by Jeep to transfer power around to the wheel with traction, I got about 24,000 miles out of the rear pads before I had to change them. I usually see north of 75,000 miles on vehicles before rear pads are needed. So now if I am in a limited traction area, like sand or know that the Jeep will be seeking traction a lot due to the terrain, I turn on the rear locker. This philosophy has made a huge impact on rear brake longevity. I am currently at almost 49,000 miles and my rear brakes are still in very good condition.

 

[Arterius2]

@Firestarter you totally didn’t read what I wrote lol.

Then again, it may be me who didn’t read what you wrote. Can’t blame me when you write an essay for a response though.

 

[Firestarter]

I read what you wrote. " Even if the front wheels are spinning. You will still get 50% traction in the rear, because front and rear are locked solid." That's not what happens. A part-time 4wd system cannot send torque to an axle that cannot develop it.

Watch this video.

@Firestarter you totally didn’t read what I wrote lol.

Then again, it may be me who didn’t read what you wrote. Can’t blame me when you write an essay for a response though.

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