Shifting the transfer case

[smokeythecat]

When my 2021 Willys was brand new it was a little difficult to get it into 4LO and even more difficult to get it out of 4LO. I finally found that what works best for me is for the vehicle to just barely be moving while I push forward on the transfer case lever. Also, it got easier after a bit of break-in.

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[YBABRAT]

Just searched and found this. I guess this is all normal. I tried 4H and it was very hard to shift. Mind you the car has 80+k miles and a few trails under its belt. Odd thing going back into 2H, it was very smooth and did not fight.

There are a few service records of maintenance done for drive train through dealer, milage and usage related. The original owner was very good with up keep. So even with that, it is extremely tight.

I actually thought because it was so difficult, I had to find some magical method to shift. Push down, pull up, pull right, pull left, where is the lock button to release? None worked other than strong arming the thing.

 

[jeepoch]

@JeepGeezer,

Michael, first off there are many misconceptions on how to shift a Transfer Case (TC). Many say it's hard until you 'break it in'. Others say that it's normal to be so difficult. Well, both are sort of right but yet still forunately, totally 'wrong'. Each and every shift from High to Low gear should be smooth and almost effortless, if performed properly.

Let's start by going through some background mechanical physics, then approach the shifting with a proper procedure.

First, the transfer case is like any other mechanical connection type of system. Each side has a gear with 'teeth' that must mate with a corresponding 'cog' in order to mesh. Granted, I'm being very simple with the concepts here just to make this easy to picture and understand. Modern Transfer Case mechanism's are way more sophisticated than this description but the physics of how this works in principal is what we're after.

When in 'gear' (either high or low, it doesn't matter), then the teeth are meshed with the corresponding cog. And all rotational shaft energy is synchronized with no loss. The input shaft from the powertrain spins at the same rate as the driveshaft connected to the differential. In 2Hi, only one drive shaft is engaged.

When shifting gears, a mechanism must disengage the meshing of the teeth and cogs from one gear and then mate (and remesh) the teeth to the cogs of the other. However, this is typically done without the benefit of a clutch. So this meshing must be done manually (by you).

Now let's consider what the TC actually does and also what it doesn't do. It provides the following:

1. Engages and disengages power to one of the driveshafts. For the JL this is the driveshaft to the front axle. The rear driveshaft is always engaged (when in 2HI). The front driveshaft is only engaged when shifting to 4HI. Note that no gearing is actually changed when shifting from 2 to 4HI or vice versa. This is why you can make this shift at highway speeds.

2. Changes gear sets from High to Low gear. This happens only in 4WD.

3. Disengages everything, both driveshafts from all gearing when in 'Neutral'.

These three things are exactly what the Transfer Case does. Nothing else. It also provides no clutching, so all gearing changes are performed manually by the force of your arm.

When things align or mesh, the shifting force is small and really easy. When the teeth and cogs don't align then the shift force is high, hard or even impossible. So the magic 'secret sauce' is to find a way to get everything to naturally align while making the shift.

The best and most practical way to accomplish this is at very low speed (not stopped). If the entire width of the gear's teeth perfectly fit the hole of the cog, then and only then can an easy shift happen. If any part of a tooth doesn't fit, then the shifting force will be high.

If you provide enough force (through muscle strength), you can actually grind part of the metal and start 'shaving' the teeth so it becomes more rounded. So for those who advocate using force to 'break-in' the TC, this is what they're doing. Rounded teeth will certainly make it appear that the shifting has become easier. There is less tooth area that needs to fit. However, with the additional side-effect of metal shavings in your TC fluid. That in and of itself has it's own set of rules regarding the law for diminishing returns over time. Rounded teeth also makes it much easier to fall out of gear as well. So keeping the teeth square as possible throughout the life of your vehicle is certainly in your best interest.

Moral of the Story: Never force the shifting into or out of gear. The shifting should always be smooth and effortless when performed properly.

OK, so how do you do that? With practice it should become remarkably easy, you'll almost never have to even think about it. The key is low velocity. There's two ways to achieve this:

On a flat surface use the engine and transmission to achieve a slow roll. Just a single mile per hour is sufficient, (a very small rotation movement of the powertrain). Once moving, place the transmission in neutral or press in the clutch. Make the shift smoothly from 4HI through Neutral (disengage) into 4LO (engage).

On an incline, with the transmission in neutral or clutch pressed, take you foot of the brake letting the vehicle roll (either forward or backward, doesn't matter) make the TC gear shift. Again it should me smooth and effortless.

Recall at very low rotational speed, either from the input shaft (the transmission) or output shaft (the wheels), the teeth will mesh with little to no effort. Each and every time.

Also reiterating again, the shifting from 2HI to 4HI (and vice-versa), there is no gearing change. The TC is only engaging or disengaging the front axle. It is safe to make this shift at any reasonable speed, but transmission neutral should be set in order to minimze powertrain torque and reduce any overall binding.

Lastly, this diatribe only applies to the low-end Transfer Cases. The higher end 'Auto' 4WD with both partial and full-time 4WD modes do have computer controlled automation that perfoms these functions. But the underlying low-level physics are always still in play.

With practice, you'll find that you'll never ever have a hard shift again. I promise.

Happy Jeeping, happy shifting.
Jay

 

[Heimkehr]

Now let's consider what the TC actually does and also what it doesn't do. It provides the following:

1. Engages and disengages power to one of the driveshafts. For the JL this is the driveshaft to the front axle. The rear driveshaft is always engaged (when in 2HI). The front driveshaft is only engaged when shifting to 4HI. Note that no gearing is actually changed when shifting from 2 to 4HI or vice versa. This is why you can make this shift at highway speeds.

N.B. -- Per the "Shifting Procedures" text in the Owner's Manual, the vehicle's recommended maximum speed shouldn't exceed 45 MPH when shifting from 2HI to 4HI or from 4HI To 2HI.

This makes sense when one considers the driving conditions that would compel use of the transfer case.

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