4wd not engaging

[Dubs Chops]

OK I will be starting a Build thread pretty soon, I love this forum and all its info,

However I have not been able to find the exact info I seek this time.


I searched and found a 1999 4 runner with a 3.4 5speed manual and rear locker. It needed a little TLC but all in all I think it will be a good base to work from.

However the 4wd will not engage, I am thinking it may be a vacuum problem but I can't find any charts showing me which lines to check,

This has a 5 speed and the j style tranfer case shifter as well. No button.

when I shift the stick to 4h or 4l nothing happens, No light on the dash, no clunk, and no click behind the guages.

What all should I be checking to start narrowing this down?

thanks again, build thread to come soon I promise.

 

[Doc2012]

Look next to the Battery. There should be two little vacuum pumps. Follow those lines down to the top of the front diff.

Those are the lines that engage the front diff. If you're not getting vacuum, they more than likely need replaced.

You can take them off and try to actuate the diff by sucking on those lines. If nothing happens, your actuator is probably bad. You can take it off and probably just manually move it to break free if it's frozen.

There are three sensors on the t-case, up by the shifter. If the connections to those are bad, your front diff won't engage either.

You should be able to feel the truck go into L. It will be more torquey, as well as rev higher with a small increase in speed. If none of that happens, then you probably have a bum t-case, and would need a new one.

 

[Dubs Chops]

It is definitely going into low. Just not engaging the front axles. My canister by the battery has about 15 lines on it running in every direction. Any chance someone could post a picture of the correct lines? Thanks for the reply BTW it is greatly appreciated.

 

[TheDurk]

My standard post on this:

Don't guess at it, troubleshoot! Start at the twin VSV's (Vacuum Switching Valves) on the driver fender wall. There are two long vacuum hoses that come up from the diff, one goes to each VSV. Check to see that one of the two hose nipples on the VSV’s has vacuum (engine running, 4WD NOT engaged. If no vacuum either side, check the check valve going to the intake manifold and look for loose hoses or a hole in the reservoir. If there is vacuum going to one hose, then put it in 4WD. See if the vacuum switches to the other hose. If it does, and no 4WD, problem is the diff actuator or the line to the diff. If it does not, then just switch the hoses and you should go into 4WD. This confirms diff is okay.

OK, switch them back. Then use a test light to see if electrical signal from the TC also switches sides of the VSV. If it does not, problem is the switch on the TC. If it does, but the vacuum does not, the problem is the VSV itself.

I start troubleshooting at the VSV's because you can figure out where the trouble is without having to climb under the truck.

As far as the hoses, start at the little plastic manifold by the VSV's on the fender wall near the battery. One hose goes to the reservoir, one goes to the check valve and then to manifold, and two go to VSV's (one to each). Then one hose from each VSV goes into a tube and down to the diff. That's it. That's from memory but I think it's right.

 

[Dubs Chops]

OK guys, one of the plugs on the transfer case is plugged in but the wires are just hanging loose. If I remember correctly it is the one on the passenger side about 1/3 of the way down on the transfer case. the problem is I don't know where the plug wires come from???? anyone have a schematic or picture of that so I can trace them down and splice the wires back together?

 

[Dubs Chops]

Anyone have any info on this plug I speak of above?

 

[Chandlerdoom]

I don't have my manual on me so see what plug your talking about. If I remember correctly 2 plugs for 4wd and 1 speed sensor.

Have you checked your vacuum lines yet? I don't have a picture of it but ill describe it. Front of the intake manifold there's a line that runs to the driver side fender wall (check valve in the middle blue/white) that line splits off.

When it splits it goes to the vsv, the vsv has 4 lines plugged into it and two plugs (engine side) one blue one brown. You should be looking at the vsv now

The two vacuum lines closest to the engine are the ones that go to the front diff. Turn the truck on (2wd) and see if you get vacuum from one side,
Go into 4wd and see if you get vacuum on the other line


Check out my thread as well, it may help you elimate some things

 

[Dubs Chops]

OK it is indeed the wires that run to the transfer case that tell it you have engaged 4wd. the have been caught on something and ripped out right at the sensor they plug into on the transfer case. I verified this by putting it in 4wd and bridging the wires. bingo 4wd light comes on.

the problem is the sensor is too hard to get to to remove and fix it. would it be okay to just run the wires to a toggle in the cab?

would this eliminate the need to put the transfer case in 4wd if you just flipped the switch or would it just make the light come on and not actually engage 4wd.

anyone see a problem just running them to a toggle?

 

[Diagram14]

I thought the sensors just sensed whether or not you were in 4x4 and turned on the dash light if they all agreed. It sounds to me like you've been getting 4x4 the whole time but with one bad sensor the dash light cant turn on. With the J-shift TC you are physically engaging the TC, nothing electronic for that side of things. Just solder your wires back together and heat shrink them real well and youre probably good to go. Assuming there are no other issues, knock on wood.

 

[Dubs Chops]

nope I tested it. the vsv did not engage the front diff even when in 4wd. I think that sensor is what tells the vsv to switch. also I can't get to the other end of the wires without dropping the tras so that is why I want to just put in a nice toggle in the cab.

 

[TheDurk]

nope I tested it. the vsv did not engage the front diff even when in 4wd. I think that sensor is what tells the vsv to switch. also I can't get to the other end of the wires without dropping the tras so that is why I want to just put in a nice toggle in the cab.

Yes, you're right, except that it causes the front diff to engage, not the TC. That is done by the J-handle. D14--the sensor does indeed cause the diff to engage, it's not for the light, except indirectly. The light comes on when the front diff engages, which only happens when the TC is engaged in 4H or 4L.

I see no reason why an SPDT in the cab, wired to switch 12V+ between the VSV solenoids would not work. It would have to have a key on source, as those solenoids would run the battery down if left energized with the engine off.

Do you go into 4wd if you swap the hoses as I described above? This confirms there is nothing wrong with the diff.

 

[Doc2012]

You don't have to "drop the trans."

Go inside the cab, and take out the center console. you have a manual, so I can't tell you how to do this....

Take off the shift cover by gently pulling up on it.

Figure out how to get the boot off( I have an auto, so I'm not familiar with the manual boot placement).

Look down at your t-case shifter. See the 4 bolts? Take those out. 12mm. The shifter will then come through the cab.

You should be able to get to that switch now. If not, continue on.....

Get a jack, and place it under the tranny cross member.

Take the 2 14mm bolts out of the tranny crossmember on each side of the frame side.

GENTLY lower the jack. This will cause your tranny to drop a couple inches. DON'T LEAVE IT LIKE THIS FOR EXTENDED PERIODS OF TIME! It will stress out your motor mounts.

you should have even more room to get to that sensor now.

 

[Dubs Chops]

Yes, you're right, except that it causes the front diff to engage, not the TC. That is done by the J-handle. D14--the sensor does indeed cause the diff to engage, it's not for the light, except indirectly. The light comes on when the front diff engages, which only happens when the TC is engaged in 4H or 4L.

I see no reason why an SPDT in the cab, wired to switch 12V+ between the VSV solenoids would not work. It would have to have a key on source, as those solenoids would run the battery down if left energized with the engine off.

Do you go into 4wd if you swap the hoses as I described above? This confirms there is nothing wrong with the diff.

the two wires I would wire into the switch already have power when the key is on. this is what the sensor does I am pretty sure is senses the tcase has been engaged to 4wd and bridges the wires. why wouldnt a spst work to just do the same thing?

Also yes I engaged the 4wd by switching the vsv hoses and it worked great!

 

[JamesDean91]

If you wire the wires up to a switch it will pretty much give you a poor mans 2 low mod, the front shaft will spin but it will not engage the front diff until you flip the switch.
I have the push button 4wd and I only had to unhook a plug to be able to go into 4h-4lo now when I put it into either without pushing the 4wd button the front diff won't engage and now I have a 2lo. Cheap twin stick.

 

[TheDurk]

the two wires I would wire into the switch already have power when the key is on. this is what the sensor does I am pretty sure is senses the tcase has been engaged to 4wd and bridges the wires. why wouldnt a spst work to just do the same thing?

Also yes I engaged the 4wd by switching the vsv hoses and it worked great!

I thought you said you could not access those wires and I assumed you were planning to apply power direct to the VSV's. If you are just bridging the T-case sensor, then the SPST will work.

What needs to happen is power needs to be applied to either the blue VSV or the brown VSV, but never both, because you need vacuum on one hose but not on the other.

 

[Dubs Chops]

Cool,

Thanks everyone I appreciate the help. SPST toggle it is and now I have 2 Low also =]


One more question though. if I put it in 4h but do not flip the switch is there anything different happening than if I was in 2h?

 

[TheDurk]

Cool,

Thanks everyone I appreciate the help. SPST toggle it is and now I have 2 Low also =]


One more question though. if I put it in 4h but do not flip the switch is there anything different happening than if I was in 2h?

The TC will engage the front propeller shaft but the power will not pass through the diff to the wheels. So you will be spinning metal unnecessarily with no gain in performance. Similar to driving in 4wd with locking hubs left unlocked.

 

[Dubs Chops]

Durk,

Thanks man, last question what about reverse of that switch on but tcase in 2H?

 

[TheDurk]

Durk,

Thanks man, last question what about reverse of that switch on but tcase in 2H?

Then the wheels will spin the front shaft through the diff, Same result: unnecessary spinning metal and no benefit in driveability.

 

[MR.H]

I am also having a problem with the 4wd system. Seems like everyone that has is using the automatic.

To add to the discussion, what is this TC people keep referring too. I have isolated the problem, and it seems that there is no signal coming from the J shifter to tell the VSV to switch vacuum. Hopefully this isnt a major fix. Thank you for your input.