4wd problem

[Chandlerdoom]

I have a j style 4wd shifter and auto for reference.

So about a month ago I decided to go into 4wd because we were supposed to get snow the next day. Put it in 4hi and nothing so I drive around for about 30 mins to see if it would finally go in, still nothing. Decide to park while I search for clues on the Internet and about 20 mins of sitting there it just goes into 4wd, so I drive around and put it back into 2wd and park it.

I assumed it was just cold and needed to get warmed up or whatever. So for the past week I've been trying to get it in 4wd again only with no luck. I've tried 4lo and forward/reverse with nothing.

I do get a click when I go into 4wd, no light on the dash. I've looked at the vsv and checked for vacuum. And I only removed the lines closest to the connections and vacuum on one side with 2wd and it switches when I go to 4wd with vacuum. I've looked for disconnected lines.

Should I check the back two vacuum lines as well? What should I have from them? What electrical connections should I look at? And were are they located?

Also when I engaged 4lo and drove for a bit it was really really hard to get out (two hand pull most of my strength) if that leads to anything

 

[Chandlerdoom]

Another thing front drive shaft does spin in 2wd, and does not spin in 4wd. The wheels can be spun freely in 4wd with the drive shaft locked. So could it be the TC still? Or can the ADD actuator fork lock the driveshaft without the TC?

 

[motobrad14]

Does it shift smoothly back into 2WD? maybe Its in the case and not the Front diff?? Maybe?> Never had problems with mine but I'd sure like to know what to do if I ever come across this issue.

 

[Chandlerdoom]

Yeah 2 to 4hi is fine, just getting it out of 4lo to n was something else.

I also removed both vacuum lines that go to the actuator and tried to rotate the drive shaft, still locked. Would removing those lines and still having the drive shaft locked put the TC out of the question?

 

[Diagram14]

The drive shaft should not be spinning at all in 2wd. How are you checking for spin? Lifting the front of the vehicle or having someone roll it slowly while you look under?

It sounds like someone might have reversed the vacuum lines on either your VSV or front diff actuator. Which is locking in the front diff while in 2wd and making the wheels spin the drive shaft. And when you shift into 4x4 its disengaging the front.

For 4lo make sure youre stopped and in Neutral before shifting in AND out.

 

[Chandlerdoom]

Guess I should clarify, I can grab the drive shaft while its parked and spin it by hand in 2wd and it will not spin by hand in 4wd. And yes parked while shifting into and out of 4lo

 

[cordrayj1]

sounds like something in the diff to me.

or. maybe a sensor is bad on the tcase

 

[Diagram14]

Guess I should clarify, I can grab the drive shaft while its parked and spin it by hand in 2wd and it will not spin by hand in 4wd.

Well, that makes me take back what I said above about the vacuum, for now...

Test: shift into 4hi, park on flat surface, apply ebrake, chock rear wheels, jack front end (one or both wheels off ground), transmission in neutral (only after wheels are chocked and ebrake applied!)...

...Spin one of the free wheels,

a) drive shaft does not spin = problem in front diff. Could be as simple as a sticky/gummed up actuator. Could be something worse. Consider the mileage on your truck vs. how long its been since 4x4 was used. If it is high and years consider changing the diff fluid and pulling the actuator for cleaning as a starting point.

b) drive shaft does spin = its probably just a bad sensor as cordrayj1 stated. Which sensor?, happy researching. I think there are three; one on the front diff to on the TC.

Note: often times while spinning the a lifted wheel the diff will engage. So listen for the click.

 

[Chandlerdoom]

I did that but it was in park, wheel spun drive shaft stayed still. Should I try in N?

Anyone have any knowledge of taking the actuator off? The top bolts looked a little hard to reach. Being that the last time it went into 4wd it took some time so I want to say that it's gummed up

Ill have to wait till I'm home on Monday to check anything else.

 

[Diagram14]

Guess I should clarify, I can grab the drive shaft while its parked and spin it by hand in 2wd and it will not spin by hand in 4wd. And yes parked while shifting into and out of 4lo

Just trying to work with what you're putting out.

Yes you need to do it again in neutral. With the transmission in P it is going to lock the drive shaft with it. That is why you could spin the wheel and the drive shaft would not move. Which also means that your front diff was not engaged, because in 4hi while in park you would not be able to spin the front wheel. Assuming only one wheel was lifted, if both were lifted the far side would spin opposite the one in your hand.

Let us know what Monday produces.

 

[Chandlerdoom]

Did it again and drive shaft would not move when I spun one wheel, so it's the front diff. Not sure what I should check first, I'd like to say its the actuator because it took so long to go into 4wd the last time, and I can't see that being an sensor problem.

 

[Diagram14]

Vacuum test time. There are two vacuum lines that plug into the actuator on the back side of the diff. One will pull vacuum in 2wd and the other in 4wd.

When I troubleshooted my 4x4 I found that the previous owner had at some point pull the motor and smashed a vacuum line in the motor mount upon reinstallation. If you end up not having vacuum trace those lines up to the VSV (vacuum switch unit) and see if youre getting pull at the nipples, ruling out a hole in the line or a faulty VSV.

 

[Chandlerdoom]

Well I can finally post, server was too busy yesterday.

Pulled the vacuum lines on the front diff and one was kind of crusty and did not have vacuum at first and after I pulled the line off and put it back on it started to get some vacuum, still no 4wd

So should I pull the actuator and clean it up?

 

[Diagram14]

If youre certain you have vacuum in one line while in 2wd and vacuum in the other line while in 4wd then it would be time to de-gum the actuator. Being that youre getting vacuum down at the diff means the sensors are working.

If you were able to somehow get it into 4wd I might consider swapping the fluid to see if running it for a bit would free things up. I wonder if SeaFoam would be a consideration for a front diff, maybe someone else will chime in on that.

 

[Chandlerdoom]

I did get vacuum from both lines, and I tried a rubber mallet on the actuator to give it some motivation with no luck.

Anyone have experience removing the actuator, it seems in a difficult place to reach.

 

[revenantdead]

shift in to 4hi in park. switch the out put lines on the VSV's. see if your light comes on. if it DOES you may have some issue with the 4WD relay.

 

[Chandlerdoom]

I wish that was the issue, at least I'd be able to get into 4wd

 

[Diagram14]

This guy has a different T-case than you but his troubleshooting approach is pretty organized and thorough. 4x4 problems

 

[Chandlerdoom]

Well well I'm laying under the truck and decide to suck on the vacuum line to see if I can hear it move. I hear it move and grab the driveshaft and it locked in. Turned it on and put it in 4wd and it turns on. I go play in the snow for a bit and drive home and see if I can turn it off and back on. No luck


So now I need to figue out how to get this actuator off to clean it and replace the lower vacuum lines

 

[Diagram14]

The other vacuum line should pull the front diff back into 2wd. A possibility is that there just isnt enough vacuum coming through VSV to move the actuator.