4x4 not working!

[Amick99]

Ash,

The JL Sahara comes standard with the NV241 Command-Trac or the optional MP3022 Select-Trac Transfer cases. By the sound of it you have the standard Command-Trac. If this is the case your shifter knob should look like: 2Hi, 4Hi, N, 4Lo and has the 2.72:1 (rather than the 4.0:1) gear ratio.

This transfer case is purely 'manual'. In other words there is no automatic full or part time 4WD. When you take it from 2Hi to either 4Hi or 4Lo you are in 4WD regardless of what your cluster lights illuminate. The trouble you are experiencing can likely be as simple as a lever sensor malfunction.

It can also be related to the FAD (front axle disconnect). This is a device that disconnects the front axle so that each wheel can rotate independently without actually turning each of the planetary gears on the differential when in 2WD. This provides additional fuel savings when the front differential is not being powered. However, if the control computer can't determine the position of the sprocket in the FAD, that is whether or not the two sides of the axle are actually connected, this could prevent 4WD functions (like sway bar disconnect or engagement of the lockers). But since you have a Sahara you should have neither, or just the rear LSD. But this is most probably the cause of your 4WD issues.

Regardless, rest assured that by placing your transfer case lever in anything but 2Hi, you are certainly in 4WD.

Jay

Thank you. I also am leaning towards the fad. Seems like a lot of others have had issues with that as well. Going to be calling the local dealer this week. I was hoping it was something simple that I could check at home. But it doesn’t appear so.

Sponsored

 

[No Spark V6]

Does the front driveshaft rotate when you're in 4h?

 

[jeepoch]

Does the front driveshaft rotate when you're in 4h?

Of course it does. Both axles need to be powered in any 4WD mode.

 

[mwilk012]

Ash,

The JL Sahara comes standard with the NV241 Command-Trac or the optional MP3022 Select-Trac Transfer cases. By the sound of it you have the standard Command-Trac. If this is the case your shifter knob should look like: 2Hi, 4Hi, N, 4Lo and has the 2.72:1 (rather than the 4.0:1) gear ratio.

This transfer case is purely 'manual'. In other words there is no automatic full or part time 4WD. When you take it from 2Hi to either 4Hi or 4Lo you are in 4WD regardless of what your cluster lights illuminate. The trouble you are experiencing can likely be as simple as a lever sensor malfunction.

It can also be related to the FAD (front axle disconnect). This is a device that disconnects the front axle so that each wheel can rotate independently without actually turning each of the planetary gears on the differential when in 2WD. This provides additional fuel savings when the front differential is not being powered. However, if the control computer can't determine the position of the sprocket in the FAD, that is whether or not the two sides of the axle are actually connected, this could prevent 4WD functions (like sway bar disconnect or engagement of the lockers). But since you have a Sahara you should have neither, or just the rear LSD. But this is most probably the cause of your 4WD issues.

Regardless, rest assured that by placing your transfer case lever in anything but 2Hi, you are certainly in 4WD.

[Edit]
Of course if your FAD is stuck open (disconnected), then you'll only be 3WD. Two rear wheels but only one front wheel would be powered.

Jay

Jay, you are wrong.

With any 4wd system fault that causes the FAD to disconnect, you are in 2wd. The front differential will prevent power transfer to either of the front wheels even though the front driveshaft is turning.

 

[jeepoch]

Jay, you are wrong.

With any 4wd system fault that causes the FAD to disconnect, you are in 2wd. The front differential will prevent power transfer to either of the front wheels even though the front driveshaft is turning.

Not completely accurate. The differential will apply some torque but essentially just because of brake lock differential (BLD). Recall, BLD is always enabled on the JL.

But in your defense, yes a purely open diff would behave as you describe.

Jay

 

[mwilk012]

Not completely accurate. The differential will apply some torque but essentially just because of brake lock differential (BLD). Recall, BLD is always enabled on the JL.

But in your defense, yes a purely open diff would behave as you describe.

Jay

This is the function of the FAD. With a 4wd system fault active, you WILL NOT have 4wd. The transfer case will mechanically engage, but all other systems will prevent actual operation of the 4wd function.

And to the OP, arbitrarily targeting the FAD itself as the source of the problem is misguided. Something as simple as a transfer case shift cable adjustment may be necessary.

 

[Amick99]

This is the function of the FAD. With a 4wd system fault active, you WILL NOT have 4wd. The transfer case will mechanically engage, but all other systems will prevent actual operation of the 4wd function.

And to the OP, arbitrarily targeting the FAD itself as the source of the problem is misguided. Something as simple as a transfer case shift cable adjustment may be necessary.

That’s true I don’t know for certain if it’s the fad or not. I just don’t feel or hear any movement from the fad when I’m underneath it and had someone else shift it into 4wd. Looks like a trip to the dealer is in my future

 

[jeepoch]

@mwilk012,

As long as the front drive shaft is powered, all the mechanics of the front axle is in play. Granted the control computer might not like it and prevent some other functionality (like preventing the sway bar disconnect). But all things that can spin, will spin from the torque applied from both drive shafts. The control computer cannot disconnect the transfer case. That can only be done by the driver from the shift lever in the cockpit.

Jay

 

[mwilk012]

@mwilk012,

As long as the front drive shaft is powered, all the mechanics of the front axle is in play. Granted the control computer might not like it and prevent some other functionality (like preventing the sway bar disconnect). But all things that can spin, will spin from the torque applied from both drive shafts. The control computer cannot disconnect the transfer case. That can only be done by the driver from the shift lever in the cockpit.

Jay

The front axle disconnect will prevent power transmission to the front wheels. The transfer case providespowe to the front driveshaft but that does f* all to get you out of a mud hole.

 

[jeepoch]

The front axle disconnect will prevent power transmission to the front wheels. The transfer case providespowe to the front driveshaft but that does f* all to get you out of a mud hole.

Agreed. But the really nice thing about these JL's with an open diff and BLD, (and even with a broken disengaged FAD), is that you still have some available torque being applied to at least one front wheel. Granted nowhere near as much as the torque being delivered to the rear wheels, but any amount of torque being applied in any of the four corners in order to help maintain traction is way better than none.

Three wheel drive (even if just partial) is better than two wheel drive any day of the week. Especially on Sunday when you find yourself in that mud-hole, driving home from church in your fancy going to meeting duds.

Cheers,
Jay

 

[No Spark V6]

Of course it does. Both axles need to be powered in any 4WD mode.

I'm aware that it should... my post was directed at the OP since he's having issues.

 

[jeepoch]

@mwilk012,

Also what may be confusing is that the Front Axle Disconnect is a little bit of a misnomer. It doesn't disconnect the entire axle, it only disconnects one wheel on that axle. The other wheel is still connected to the differential and drive shaft.

It's primary purpose has nothing to do at all with 4WD, at least not directly. It's intended to disconnect the spline within one side of the axle from being connected to the differential in unpowered 2WD mode. This reduces friction from rotating the planetary gears (under load) within the differential when that axle is not powered (2WD). Thus saving on excess drag and helping achieve stated CAFE goals.

In 4WD, the FAD is engaged allowing both wheels on that axle to be powered. However, with any open diff, the wheel that's spinning fastest (the one with the least resistance) gets most of the applied torque.

Enter either Brake Lock Differential (BLD) or lockers. With lockers things are easier to visualize. Each side of the axle are locked together so that they always rotate at the same rate regardless of any wheel slip. So with locked front and rear axles as long as just one wheel (any one) grips the ground with sufficient traction then momentum can be maintained.

Whereas with open diffs, since any slipping wheel gets the majority of the torque, you need at least one axle with both wheels that grip in order to maintain momentum.

Enter the JL's BLD functionality. It applies braking action (via the ABS system) to any wheel on either axle that's spinning faster than it's other side, (the slipping wheel). This allows proportionately more torque to be applied to the other, non-slipping wheel. This is tremendously advantageous in 4WD applications. This means that instead of needed two gripping wheels on the same axle, you now only need two gripping wheels on either axle in order to maintain momentum. Certainly not as good as locked axles but way (way) better than purely open diffs.

Now the case that started this all, 4WD with a disconnected FAD. Recall, the FAD should only ever be disconnected in 2WD on the unpowered front axle. However in 4WD mode, the transfer case applies torque to the front axle in either 4Hi or 4Lo depending on the shift lever position. Regardless, the controller should engage the FAD in any 4WD setting. But for some reason the FAD does not engage and only one wheel is connected to the differential.

This then means the wheel that the FAD disconnects is always 'slipping' so it should get nearly all of the applied torque. On a purely open diff the disconnected spline spins as fast as that torque would allow. No power is physically applied anywhere but to an unloaded shaft.

But with BLD, the brakes are now being applied to any slipping wheel. Since the speed sensors are attached to the wheels and not the splines within the axle and there is at least one connected wheel that will get some (even if very little) torque, this should result in that one attached wheel to spin faster than the physically disconnected one (due to the disconnected FAD). Therefore, the BLD will apply more braking action which will only increase the amount of applied torque to that one connected wheel.

Granted there is the law of minimizing return where the applied torque will maximize at only some fractional point, but again, something is better than nothing. So in the 4WD mode with a dysfunctional FAD, you still have the potential of realizing at least some amount of 3WD.

Clearly this is not something you would want to live with since the brake pad on that wheel would be degraded faster but it would at least be better in some 4WD condition better than nothing at all.

So if it were me finding myself in some driving condition which requires 4WD, either 4Hi or 4Lo with a disconnected FAD, I'd still use 4WD and cope with the potential 3WD result.

Much, much better than simply leaving my rig in 2WD in order to prevent any cluster warnings.

For what this diatribe is worth.
Best regards,
Jay

 

[mwilk012]

Jay, I’m not reading that and I guarantee you almost nobody else will either. With the fad disconnected you don’t have 4wd. Simple as that. BLD will not function on the front axle with a 4wd fault. Do some testing yourself with 4 wheels off the ground if you like.

 

[jeepoch]

For the record BLD is always enabled, 4WD fault or not. As long as one wheel is spinning faster than the other on the same axle (while going straight), BLD will apply braking action on just that specific wheel.

If the FAD is disconnected (no matter the reason) one wheel is still being powered whenever the transfer case has engaged the front drive shaft (4WD fault or not). If that powered wheel slips, spins faster than the other one (even if disconnected), BLD will still be applied. Thus increasing the available torque to just that connected wheel.

Three wheel drive is better than two every day of the week. Of course 4WD is so much better. And yes, that can only occur with a functional FAD.

Jay

 

[mwilk012]

For the record BLD is always enabled, 4WD fault or not. As long as one wheel is spinning faster than the other on the same axle (while going straight), BLD will apply braking action on just that specific wheel.

If the FAD is disconnected (no matter the reason) one wheel is still being powered whenever the transfer case has engaged the front drive shaft (4WD fault or not). If that powered wheel slips, spins faster than the other one (even if disconnected), BLD will still be applied. Thus increasing the available torque to just that connected wheel.

Three wheel drive is better than two every day of the week. Of course 4WD is so much better. And yes, that can only occur with a functional FAD.

Jay

Jay, you’re being stubborn here for no good reason. With the FAD disconnected, neither of the front wheels will spin. BLD will not work.

Sponsored