Shift Solenoid/4WD theory of operation

[wpurple]

(1997 5 speed stick) Had an issue with getting stuck in 4WD, 4WD and 4WL flashing on and off every other second.
In a quick attempt to get it to 2WD I removed the shift soloniod and moved the transfer case position to N thinking no 4wd...Well that put all in N, no go forward at all, I was like ??? thinking it was always a direct link to the rear diff and 4WD and 4WL was commanded??

So, I moved it to the H position and back to going....driving today it didn't seem like it was in 4WD, I could spin the rear tires and I didn't "hear" the front diff...

Can someone clarify my experiance? My expectations that you move the x-fer case to H you get 4WHigh, you move it to L you get 4WD low, you move it to N you have 2WD...

Thank You!

 

[Fix4Dirt]

(1997 5 speed stick) Had an issue with getting stuck in 4WD, 4WD and 4WL flashing on and off every other second.
In a quick attempt to get it to 2WD I removed the shift soloniod and moved the transfer case position to N thinking no 4wd...Well that put all in N, no go forward at all, I was like ??? thinking it was always a direct link to the rear diff and 4WD and 4WL was commanded??

So, I moved it to the H position and back to going....driving today it didn't seem like it was in 4WD, I could spin the rear tires and I didn't "hear" the front diff...

Can someone clarify my experiance? My expectations that you move the x-fer case to H you get 4WHigh, you move it to L you get 4WD low, you move it to N you have 2WD...

Thank You!

If you have the BW4405, which Im 99.9% you do, the HLN only controls the range. Its not like your traditional stab it from 2h into 4h transfer case you might be used to.

The front wheels are controlled by a clutch in the case. HLN is only the range. High means 2wd with the front clutch disengaged, 4H with the front clutch engaged, Low means 2low with the front clutch disengaged (if you do the brown wire mod you can achieve this) and 4L.

Neutral is to put the case into neutral for tings like flat towing

Essentially, the shift motor only controls the range, the clutch controls if the front wheels are powered or not.

The clutch is a ball and ramp assembly that when the elctromagnet is engaged it engages the fornt wheels.

 

[wpurple]

If you have the BW4405, which Im 99.9% you do, the HLN only controls the range. Its not like your traditional stab it from 2h into 4h transfer case you might be used to.

The front wheels are controlled by a clutch in the case. HLN is only the range. High means 2wd with the front clutch disengaged, 4H with the front clutch engaged, Low means 2low with the front clutch disengaged (if you do the brown wire mod you can achieve this) and 4L.

Neutral is to put the case into neutral for tings like flat towing

Essentially, the shift motor only controls the range, the clutch controls if the front wheels are powered or not.

The clutch is a ball and ramp assembly that when the elctromagnet is engaged it engages the fornt wheels.

So, if the front diff is stuck engaged its the clutch? And I assume in order to troubleshoot/repair the diff has to be removed and disassembled?
And the rear wheels are controlled also by the clutch? Is there anyway to force the truck to 2WD?

 

[C420sailor]

something with the clutch, yes. Whether it’s electrically or mechanically stuck on, you’ll need to do some tests. But as mentioned, the shift motor controls the gear reduction in the case. L drops the ratio down into that low range granny gear, H is your normal high range ratio. Clutch engagement is controlled via pulse width modulation of the clutch.

 

[wpurple]

something with the clutch, yes. Whether it’s electrically or mechanically stuck on, you’ll need to do some tests. But as mentioned, the shift motor controls the gear reduction in the case. L drops the ratio down into that low range granny gear, H is your normal high range ratio. Clutch engagement is controlled via pulse width modulation of the clutch.

Tnank you..will look up the schematic tomorrow and do some troubleshooting.

 

[C420sailor]

It should de-energize with the truck off. So if the front shaft is locked up with the truck off, likely a mechanical issue.

 

[Fix4Dirt]

Did 97 have CAD?

It should de-energize with the truck off. So if the front shaft is locked up with the truck off, likely a mechanical issue.

 

[amj441]

here is a full description of the transfer case. listed there is a electromechanical ball ramp clutch.

That clutch gets power on a brown wire going to the transfer case. as seen here:

verify that wire does not have power going to it when you are in 2wd or the truck is off.

good luck hope this helps

 

[wpurple]

View attachment 460601

here is a full description of the transfer case. listed there is a electromechanical ball ramp clutch.

That clutch gets power on a brown wire going to the transfer case. as seen here:

View attachment 460602

verify that wire does not have power going to it when you are in 2wd or the truck is off.

good luck hope this helps

Thank you for this, excellent information. Drive around yesterday and it appears the clutch released as I do not hear the front diff and I can spin the rear tire. The connector does have some corrosion so my first step is to clean that up. Only 51K on the clock and the truck has been used very seldom over the years, and even less in 4WD mode, not sure of lack of use can lazy the clutch. (Most of the mileage is from the first 15 years..)

 

[amj441]

Thank you for this, excellent information. Drive around yesterday and it appears the clutch released as I do not hear the front diff and I can spin the rear tire. The connector does have some corrosion so my first step is to clean that up. Only 51K on the clock and the truck has been used very seldom over the years, and even less in 4WD mode, not sure of lack of use can lazy the clutch. (Most of the mileage is from the first 15 years..)

a lack of use can definitely get a clutch stuck. the only 4wd vehicle i had was a grand cherokee i got for free with 250k miles on it. I found the full time 4wd would lock up like part time 4wd or 4lo. Its supposed to have a clutch that lets it slip partially while its in full time. The transfer case had low fluid in it and that clutch had seized. I filled it with some new fluid and let it soak a day and then took it to a cul-de-sac and creeped the jeep until it would bind, and slowly move fowards and reverse. eventually the clutch broke free and operated as it should.

glad yours broke free/released. Double check that fluid level next time you get the chance.

 

[410Fortune]

FYI the t case does have a N position and that is between 2wd and 4hi
Will leave you in neutral if the pointer is directed to the n you won’t get front or rear axles

The 97 should not have a cad, only 95-96 4.0 trucks had that
Cad is center axle disconnect located on the front differential

I believe your 97 is control Trac awd and the issues in the t case could be related

The t case shift motors get lazy when not used… good idea to exercise them regularly

 

[Fix4Dirt]

The t case shift motors get lazy when not used… good idea to exercise them regularly

They can get lazy? Hmmm wouldnt put up with lazy shifter hahahaha I use my 4x4 weekly if not more. (thread hijack over)

 

[wpurple]

UPDATE: Changed the fluid, it was changed a couple years ago and no more than a few thousand miles and it was silvery so I assume from the clutches.
Before the fluid change it didn't bind up on moderate cornering so I thought 4WD clutch disengaged, but a tight corner it still did. Hummm
so I had previously brown wire mod'd it, so I reached under the seat and cut the wire and bingo, couldn't get it to bind.
(I used a test light on the wire and it lit when in auto, going to do some voltage measurements. Strange that if I drove on gravel it would just spin the rear wheels...)

 

[wollimann]

I used a test light on the wire and it lit when in auto

There are 5V in auto all the time at the brown wire,
if the rear tires spin a little the brown wire get a pulsed 12V on the coil,
coil housing engages the clutch, clutch engages the front wheels.

Changed the fluid, it was changed a couple years ago and no more than a few thousand miles and it was silvery

The silvery particles came from the internal transfer case oil pump

and maybe from a worn out
rear output bearing seat (one of the known issues, bearing rotate in its seat).