Shifting Issue into 4WD

[Renegade]

Yes
and I believe my book says 45 mph. It's got to connect something spinning road speed to something not spinning. (front drive shaft)

Yes, but it’s actually even more complex than that. While moving in 2wd, the t-case and front axle disconnect are both disengaged. The left front tire is rotating forward, the driveshaft is stationary, and the right front inner axle shaft is turning BACKWARDS. The t-case needs to engage the driveshaft, the front inner shaft has to change direction, then the FAD has to engage. I’m really not sure how all of this happens smoothly. I actually had difficulty disengaging 4wd this weekend. I was climbing a muddy hill, attempted to disengage 4wd in effort to spin the rear around, and the front axle remained engaged despite the shifter having been moved back to 2wd. The computer is controlling more than we are aware of here.

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[ShadowsPapa]

Yes, but it’s actually even more complex than that. While moving in 2wd, the t-case and front axle disconnect are both disengaged. The left front tire is rotating forward, the driveshaft is stationary, and the right front inner axle shaft is turning BACKWARDS. The t-case needs to engage the driveshaft, the front inner shaft has to change direction, then the FAD has to engage. I’m really not sure how all of this happens smoothly. I actually had difficulty disengaging 4wd this weekend. I was climbing a muddy hill, attempted to disengage 4wd in effort to spin the rear around, and the front axle remained engaged despite the shifter having been moved back to 2wd. The computer is controlling more than we are aware of here.

I know - I rebuild differentials - however in the past I've been smacked for trying to explain the details and tech aspects.
So I tried to dumb it down.
I sort of rather slightly doubt the electronics was doing that. Likely force on the axle parts was holding things in place - or, traction or stability control kicked in.
There should be an interlock that prevents transfer case engagement if the axle doesn't engage, and axle disengagement if the transfer case is still engaged and so on.
In any case, if the front axle was still engaged but the transfer case disengaged the differential action inside the front carrier would allow the L and R wheels to turn independently like any other differential - they'd not be locked together (or is this a Rubicon with lockers?)
With my Overland, even if the front axle stayed locked, but the t-case disengaged it would cause no issues- it would simply spin the front drive shaft and load the vehicle a bit more than if it was fully disengaged. The front wheels would still turn independently of each other, you could raise a front corner and spin a tire on one side without effort.

Yes, there's great speed in the axle rotations, compounded by the fact that the front left will, in forward motion, be turning as expected as will the right outer axle end - with the right wheel. However, due to the action of the differential gears - those within the carrier - the axle side gears and spiders, the right INNER axle half will be turning the opposite direction, same speed as the left axle because those carrier gears reverse the motion. So you have the right axle turning forward at road speed while the right inner axle is spinning the other direction, same speed as the outer axle but opposite.

In the earlier axle systems, in the 1980s, the axle engagement was a simple sleeve and NOT synchronized. But the transfer case was synchronized. So you had to stop to engage or disengage 4 wheel drive. Then some systems deleted the front axle disconnect and you only disengaged the transfer case - the front drive shaft still spun. Some people when the axle vacuum motor failed went inside and moved the sleeve over and locked the fork in place with a hose clamp, locking the axle halves together, so they could "shift on the fly".
Later they synchronized the front axle disconnect system as well, so you could at least engage or disengage at some sort of speed - usually limited to about 45 mph.

(Transfer cases, anyone?? This is part of my stash of springs and transfer cases, heads, transmissions and front and rear differentials as I know one or two people (not in this thread, however) don't believe I've touched the stuff. I gave away a transfer case and transmission last year. )

 

[Renegade]

I know - I rebuild differentials - however in the past I've been smacked for trying to explain the details and tech aspects.
So I tried to dumb it down.
I sort of rather slightly doubt the electronics was doing that. Likely force on the axle parts was holding things in place - or, traction or stability control kicked in.
There should be an interlock that prevents transfer case engagement if the axle doesn't engage, and axle disengagement if the transfer case is still engaged and so on.
In any case, if the front axle was still engaged but the transfer case disengaged the differential action inside the front carrier would allow the L and R wheels to turn independently like any other differential - they'd not be locked together (or is this a Rubicon with lockers?)
With my Overland, even if the front axle stayed locked, but the t-case disengaged it would cause no issues- it would simply spin the front drive shaft and load the vehicle a bit more than if it was fully disengaged. The front wheels would still turn independently of each other, you could raise a front corner and spin a tire on one side without effort.

Yes, there's great speed in the axle rotations, compounded by the fact that the front left will, in forward motion, be turning as expected as will the right outer axle end - with the right wheel. However, due to the action of the differential gears - those within the carrier - the axle side gears and spiders, the right INNER axle half will be turning the opposite direction, same speed as the left axle because those carrier gears reverse the motion. So you have the right axle turning forward at road speed while the right inner axle is spinning the other direction, same speed as the outer axle but opposite.

In the earlier axle systems, in the 1980s, the axle engagement was a simple sleeve and NOT synchronized. But the transfer case was synchronized. So you had to stop to engage or disengage 4 wheel drive. Then some systems deleted the front axle disconnect and you only disengaged the transfer case - the front drive shaft still spun. Some people when the axle vacuum motor failed went inside and moved the sleeve over and locked the fork in place with a hose clamp, locking the axle halves together, so they could "shift on the fly".
Later they synchronized the front axle disconnect system as well, so you could at least engage or disengage at some sort of speed - usually limited to about 45 mph.

(Transfer cases, anyone?? This is part of my stash of springs and transfer cases, heads, transmissions and front and rear differentials as I know one or two people (not in this thread, however) don't believe I've touched the stuff. I gave away a transfer case and transmission last year. )

I hated the old vacuum disconnect systems. I actually did a trail repair on my ‘87 YJ by inserting a large nut on the shift fork shaft to permanently engage the shift fork. I’m not really liking what the new electric FAD system does at this point either...

 

[ShadowsPapa]

I hated the old vacuum disconnect systems. I actually did a trail repair on my ‘87 YJ by inserting a large nut on the shift fork shaft to permanently engage the shift fork. I’m not really liking what the new electric FAD system does at this point either...

You were not alone in disliking the vacuum system. It was complex, lots of hoses and lines and the connectors would get oil on them and swell or crack, sometimes the vacuum motor diaphragm would rupture.......... leaving you to do what you did.
I have two spares (one used, one new) for the transfer case and two spares (one used and one new in box) for the front axle on my SX4.
I grab them when I can find them.

 

[hjdca]

On my manual Gladiator, I had a hard time the first time going from 4WH to 4WL. After a couple of off-road days and about 15 miles in 4WL including lockers, the transfer case shifts easily. For me, it was just a break-in issue.

 

[Majormajor]

All those razor sharp factory gear profiles won’t tolerate just being stuffed it to mesh at a stand still, the small motion of the drive line without an engine load will give them some progressive interaction and they will start to bed and conform to each other. Totally normal. And the noise will stop being so serious as well. Also totally normal.

Using the Rubicon as an example it takes 4 turns of the transmission output shaft to get 1 turn of the transfer case output shaft. So if the transmission output is spinning it’s going to make an awful racket unless you timed it just right where as if the transmission is in neutral or clutched and the wheels are turning now the slowly turning transfer case gear has an easier time mating to the unloaded but able to have sympathetic motion transmission.

Best explanation of this issue I have ever heard. Thank you

 

[treefrog]

Ugh. After reading this thread yesterday, I decided to run my transfer through its ranges today. This is my 8th Jeep and I ain't ever had to play with one this much to get it into low range. 4 high was no pick-nick either. This one is gonna need lots of foreplay to make her happy. Gonna have to make it a point to do this often to wear em in together whether it needs it or not.

 

[ShadowsPapa]

Ugh. After reading this thread yesterday, I decided to run my transfer through its ranges today. This is my 8th Jeep and I ain't ever had to play with one this much to get it into low range. 4 high was no pick-nick either. This one is gonna need lots of foreplay to make her happy. Gonna have to make it a point to do this often to wear em in together whether it needs it or not.

Yeah, I've had 4x4s before with transfer case shifting, but this is about the hardest shift from 2H to 4H (NOT TALKING 4L) I've had yet.

 

[Trippin01]

I just followed the directions, creep along, put in 4-hi, stop, transmission to neutral, yank'r back to 4-lo, transmission to "D" (for duh ?) and a little weight applied to that big floor pedal on the right. Seems to work just fine.

 

[PyrPatriot]

Going from 2H to 4H and vise versa is easy at any speed, as long as no tires are slipping.

To shift to 4L you need to be in neutral with the vehicle moving at 2 miles per hour. Otherwise you will stress the linkage and bind it up.

"need" is a bit of a strong word. I believe it is just hard on the system to do so standing still. But the old saying applies: you shouldn't use 4L to get unstuck. As for actually moving, actual movement does help, as the manual says not to be pressing on the accelerator while shifting into 4L

 

[MarineHawk]

They carried this over from the JK???? Wow

I'd love to say this POS design didn't result in me ending up stuck in N in the middle of no where in CO, and then cause me to get burnt to hell on my forearm getting my tcase back into gear.... But it did do just that.

I never broke mine on my '12 JKUR, but, knowing that others did, I had my local shop (when doing other things to the Jeep) find a more-permanent fix. I think they installed some type of metal e-clip or something that was permanent. I may do that again, but does anyone know the part number for the plastic bushing? In the short-term, I may just order a bunch of them to have some extra spares on hand in my recovery gear tub.

A really smart and loveable gentleman posted that on another forum: https://www.wranglerforum.com/f274/jeep-stuck-in-4wd-help-plz-162882.html#post2409702

 

[rafaelsmith]

Hmm, in every Jeep I have owned(Cherokee, TJ, JK....ive always been stopped and in N when switching into 4L. As far as I can tell, I never caused any problems or dmg being stopped when going into 4L.

As for 2wd to 4h...its always been pretty much anytime I need while at reasonable speed.

 

[WXman]

"need" is a bit of a strong word. I believe it is just hard on the system to do so standing still. But the old saying applies: you shouldn't use 4L to get unstuck. As for actually moving, actual movement does help, as the manual says not to be pressing on the accelerator while shifting into 4L

I don't think need is a strong word, because that's how the transfer case was designed to be operated. Yes, it'll go in (sometimes) if you're sitting still, but it's hard on the gear teeth. So, I think it's prudent to say that we need to do it the correct way and be moving.

 

[ShadowsPapa]

As a person who has, and still, rebuilds transmissions, differentials and other boxes - the issue is that you MAY end up with tooth butting against tooth. They have angles on the teeth so if they are offset even a little bit while shifting they will angle past each other and engage. The edges or sides of the teeth aren't blunt or flat, they have angles on them.
If you are fully stopped and the teeth butt head to head so to speak, it won't be easy and you won't be helping the shift mechanisms. You'd have to bang it hard to damage a tooth, but hey, maybe some would try.
With it coasting slow, under load, the chances are the teeth will not be butting edge to edge - and it will engage as the angles on the teeth slide past each other.
If I had a box up on my bench open for repairs, I'd video how that works and why they say transmission in neutral, road speed SLOW - so they go together no load and can gently slide past each other into engagement.
There is no synchronizer between 4H and 4L, 2 to 4H yes.

 

[Cleankat]

Funny, I tried shifting into 4H yesterday for the first time (at a stop) and it wouldn't budge.

Saw this thread and tried again this morning going 3-4mph, shifted in like butter.

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