93 Jimmy Is it possible to replace 4wd actuator system with simple cable ?

[Luka1]

My 4WD will not switch out of 4WD.

When I bought the truck, it would not switch into 4wd. That was because of vacum hoses that were burned in half. I fixed that problem, and the system has been sweet, (best 4wd I have ever had !!), up until a couple months ago.

The hoses are fine. Pulling one apart proved they were holding vacum. Unfortunately, it also proved they held a bit of tranny fluid...

Pressing the switch causes all the normal clicking sounds from under the dash/at the top of the transfer case. But it never switches out of 4wd.

There were a few times at the start of the trouble when it would switch back into 2wd if I let it sit overnight before trying again. Now it doesn't make any difference what I do, it simply will not switch.


The research starts...

My haynes manual holds absolutely nothing worthwhile on the subject.


I read all over the place here on this forum, and I think I have figured out the basic system. An actuator under the battery, some vacum lines, and the switch on the transfer case.

Switch on transfer case is probably what gets switched by the toggle switch on the dash. That feeds vacum to the actuator under the battery. The actuator pulls the cable when vacum is applied. Pulling the cable switches the TC into 4wd.

Am I right ?



Now, the postulation...

Since there was fluid in the line... (Means possible problems in the switch on the TC.) Since the lines have been a problem before... Since the actuator under the battery may well be shot now, as well...

I am wondering if I couldn't just bypass the entire system, and hook up an old manual choke cable to pull on that cable that runs between the actuator, and the transfer case ???

I am perfectly capable of setting up a system of brackets, springs, etc, to make it work correctly. IF my hunch is correct.

But I need some basic info first, that I hope that someone here can provide.

First, if you take everything else about the entire system away... WILL simply pushing or pulling on that cable, switch the transfer case into and out of 4wd ?

Second, If the answer to the first question is yes... Do you pull the cable to switch it into 4wd, or do you let the cable back in, to switch it to 4wd ?

And versey-visey, of course.

Third... If pulling the cable out of the housing switches it into 4wd... Does it switch to 4hi if you pull the cable just so much... Then switch to 4lo if you pull the cable another equal amount ???

Can someone explain all of that to me?


Now...

If the answers to those questions are,
1. Yes
2. Pull the cable to switch into 4wd.
3. Yes.

Then I will make a project of building a simple cheap solution that bypasses any future problems of this sort. I will take pictures. I will show a list of materials needed. And I will explain the process.

If my hunch is right, I can use a choke cable that can be had for less than ten dollars, or even something like an old hood release cable, etc... And some cheap nuts, bolts, metal shelf brackets, small springs, etc.

It should be a fairly simple installation with a drill and a few hand tools.


One last question...

If I am right, and can do this.. and I DO the project... Is this going to end up messing with the computer because that switch on the dash is not being used anymore ?

Thank you in advance.

[Jari]

4w drive system has nothing to do with the computer, it has it's own controller, which drives transfer case shift motor to engage 4wd. Toggle switch on the dash simply gives commands to this controller. There's a vacuum switch over the transfer case which allows vacuum to the actuator when transfer case is shifted to 4wd. Actuator pulls cable which engages front differential. There is a switch on front differential which then tells controller that 4wd is on.
If you have transmission oil in vacuum hoses it tells that this vacuum switch on the transfer case is broken. In case of repairing the system replace that switch.
Changing the system to manual should be quite easy. Just take transfer case shift motor out and install a shift cable instead of it...

[Luka1]

Originally Posted by Jari

4w drive system has nothing to do with the computer, it has it's own controller, which drives transfer case shift motor to engage 4wd. Toggle switch on the dash simply gives commands to this controller. There's a vacuum switch over the transfer case which allows vacuum to the actuator when transfer case is shifted to 4wd. Actuator pulls cable which engages front differential. There is a switch on front differential which then tells controller that 4wd is on.
If you have transmission oil in vacuum hoses it tells that this vacuum switch on the transfer case is broken. In case of repairing the system replace that switch.
Changing the system to manual should be quite easy. Just take transfer case shift motor out and install a shift cable instead of it...

Thank you for the quick reply.

I am thinking it is even simpler than that.

If leaving everything intact but the vacum system disconnected, will not ruin anything, then I am thinking that I can run a cable from the dash, out to the actuator, remove the actuator, and just use my cable, to manually do exactly what the actuator was doing.

Is that switch on the TC any sort of 'modulator' ?

What exactly does the actuator do when the vacum reaches it ?

Does it put a steady pull on that cable and lock it in where it pulls it to, or does it pull the cable once and let it go, in some sort of pattern ?

Sounds to me like that vacun switch is clickng once for 4lo. Twice for 4 hi. And twice to come back to 2wd from 4hi.

That would indicate the cable or chain is pulled on in a pattern, kinda like turning on and off a closet light.

My original assumption was that the cable from the modulator to the TC directly pushed and/or pulled on the shift linkage inside the TC. But it sounds like you are saying that the cable tells a separate motor inside the TC, what to do.

~~~

Maybe I should just go back to the beginning.

Could you describe the system to me, and explain how it works ?

ie, "The system has these basic parts"... ETc And "you push the toggle on the dash... and this happens. Then this happens... etc.

Thank you once again.

[Luka1]

Oh, and how can I get it out of 4wd for now ?

Thank you.

[Jari]

In that case you would leave transfer case in fast 4wd position and control only front differential. I guess it will work. You can't use slow 4wd then.
Switch over the TC is mechanical, when a lever inside the TC pushes it gives vacuum to the actuator.
When vacuum reaches actuator it simply pulls the cable and holds it until there is no vacuum, so steady pull.
Vacuum switch does not click, it is open allways when fast or slow 4wd is engaged and closed when 2wd is on. When you hear click it's the relay inside the controller which is driving transfer case shift motor.
Transfer case shift motor rotates a shaft in TC, which then selects 2wd (not engaged), fast 4wd and slow 4wd. Motor is outside the tc , you see it (round thing looks like a filter) just below TC.

So I try to explain it (with my not so good english):

1. you press 4wd button on the dash. LED is flashing
2. 4wd controller drives transfer case motor, which rotates until the shaft in TC is in 4wd position. This engages fron drive shaft.
3. inside TC there is a lever which pushes vacuum switch over the TC. Vacuum switch opens and gives vacuum to the actuator under the battery.
4. Actuator pulls cable and engages front differential.
5. The switch over the front differential closes and gives a signal to the 4wd controller that 4wd is engaged. LED is on.

[Jari]

Originally Posted by Luka1

Oh, and how can I get it out of 4wd for now ?

Thank you.

To get it out from 4wd, you have to remove the transfer case shift motor and manually turn selector shaft counterclockwise until front drive shaft is rotating freely.

[Luka1]

Originally Posted by Jari

To get it out from 4wd, you have to remove the transfer case shift motor and manually turn selector shaft counterclockwise until front drive shaft is rotating freely.

Ouch.

I was hoping it would be simpler than that.

Thank you again, for your time.

[Luka1]

I swapped the vacum switch for a new one.

No change.

The front diff seems wacky now. (Maybe because it was locked in the on position for so long. Now something is worn, or sticky or whatever, inside the diff.)

I am wondering...

Originally Posted by Jari

There is a switch on front differential which then tells controller that 4wd is on.

If that switch is now always telling the controller that the diff is activated... Could that be what is preventing the controller from switching the transfer case out of 4wd ?

Originally Posted by Jari

Changing the system to manual should be quite easy. Just take transfer case shift motor out and install a shift cable instead of it...

Ok, I discovered the 'posi-lok' cable system to replace the actuator. (Pretty much exactly what I was thinking of doing when I started this thread. Someone else beat me to the concept. LOL)

I am wondering if there is a similar kit/system so I can change the TC over to manual... Without having to install that center console, or something equally intrusive ?

[Jari]

You can test your vacuum switch: remove it and press the ball and then release it, if it comes back easily it's ok.
Maybe you still have transmission oil in vacuum hoses. You have to clear those hoses very carefully...