95t100dx

The truck is a 95 T100 Dx 3400 5spd.

4wd won't engage.
Checked all vacuum lines, intact, in good shape.

I got the truck up off the ground completely and tried 4l, 4h. Front driveshaft is spinning, so the transfer case is doing its job. Yet the wheels won't engage.

I switched the two vacuum lines on the actuator underneath and i felt/heard the diaphragm move and i then had 4wd. Yet when the vacuum lines are on the proper ports on the actuator, i have nothing.

Any ideas? This is driving me nuts!

572ysc

Check out your actuater assembly like take it ok and check it for movement. Sounds like you may have a problems on your hubs.

250000_yota

I wouldn't say hubs persay, as long as their the stock auto hub plates. Does the truck have manual hubs? 572 is right in saying you should pull your actuator out and check it with a vacuum pump to make sure it moves properly. I've seen alot of actuators freeze up from lack of use. When I was working for Toyota, we used to recommend that people put their vehicles in 4wd at least once a month, to prevent this exact issue.

justin_4runner

when u do put it in 4wd do u hear anything a relay under the dash? sounds like ur not getting the power sent to the silanoid on the passenger side wall, the brown one i think. it could be the shift sensor on the transfer case that tells it what postion the shifter is in. this might help...

http://www.ncttora.com/fsm/1993/susp...26addcontr.pdf go to this link....

juandelnorte

There is a lot of discussion about problems with the 4WD ADD system on T100s and 4Runners. It is helpful to have a clear understanding of how the system works, so that you can do a diagnostic run-down and isolate the problem(s).

The following information is pertinent to my 1998 T100 with ADD:

The system does not have "locking hubs." The "hubs" are always locked to the front axles. The locking/unlocking takes place at the ADD actuator, which is mounted at the left (driver's side) of the front differential. The ADD system does not lock the hubs, it locks the front axle drive system. When the vehicle is in 2WD, the front axles freewheel along with the front wheels. When the vehicle is placed into 4WD, the actuator locks the front axles, so that they are coupled to the differential output, and drive power is transferred through the transfer case, into the front differential, and out the axles.

The actuator is operated by a simple vacuum connection. Vacuum applied to one side of the actuator places it into 2WD (unlocked) mode. Vacuum applied to the other side of the actuator places it into 4WD (locked) mode. The vacuum is routed through two solenoid-operated vacuum valves on the left (driver's side) fender next to the fuse box. If 2WD is selected, the 2WD solenoid opens vacuum to the 2WD side of the actuator. If 4WD is selected, the 2WD solenoid is closed, the 4WD solenoid is opened, and vacuum is routed to the 4WD side of the actuator.

Each vacuum line has a colored stripe indicating which vacuum solenoid it connects to. The 2WD vacuum line (brown stripe) is connected to the brown solenoid, and the 4WD line (blue stripe) goes to the blue solenoid.

If you are ever stuck and need 4WD but are having problems getting the vehicle into 4WD, you may be able simply to switch the vacuum lines or connect the blue-striped vacuum line directly to engine vacuum. If everything else is working, you may be able to lock the ADD this way. Move the transfer lever inside the cab to 4WD to transfer power through the front driveshaft, and voila! This will not work if you are having a problem with the transfer case or the actuator itself, but if the problem is a transfer switch or bad solenoid, for example, this may get you out of a jam.

If you're having problems with the system, I suggest that you check the following components in order. They are more or less arranged from simple to complex:

1. Check the vacuum hoses from the solenoids to the ADD actuator. Broken or leaking hoses can prevent vacuum from being applied to the actuator.

2. Check the solenoids themselves (left fender, next to fuse box). Applying battery power to the terminals should activate that solenoid to allow vacuum through.

3. Check the transfer switch to make sure it is operating properly. The transfer switch is screwed into the top-right (passenger's side) of the transfer case and can be tested from underneath the vehicle. Replacing a malfunctioning switch practically requires dropping the transfer case for access. The transfer switch routs power to the appropriate vacuum solenoid (brown or blue), depending upon selection. A malfunctioning switch will not apply power to the correct solenoid.

4. Using a hand vacuum pump, apply a vacuum to each ADD actuator vacuum line (brown stripe and blue stripe). You should be able to use vacuum to manually set the ADD actuator in 2WD or 4WD position, depending upon which line you apply vacuum to. If you cannot move the actuator between 2WD and 4WD this way, you may have a problem with the actuator itself. Start by checking the actuator diaphragm and go from there.

I hope this is helpful!

Best wishes,
Juan

Kamey16

Hi Juan, you seem pretty knowledgable about today ADD systems. My problem is I can't move the transfer case shift lever from 2H-4H with the vehicle stopped or at any point for that matter. Any ideas? Seems to me the Add system is out of the loop for this issue? It's like the transfer case is locked in 2H.
Thanks, Kamey16

juandelnorte

Kamey16,

I'm sorry, but I'm not terribly knowledgeable about the problem you're describing. It sounds to me like there's something going on inside the transfer case that is preventing proper shifting in and out of 4WD. I assume you're depressing the clutch all the way. If the clutch is disengaging normally, then the transfer shift lever should easily allow shifting from 4H into 2H.

I might try a couple of things:
(1) Try turning the front drive shaft just a little bit while you're moving the shift lever. If the gears aren't synchronized, perhaps a little bit of movement might line things up and make shifting possible.

(2) Check to see if the front drive shaft spins by hand. With the transfer case in 4H and the ADD system disengaged, you should be able to turn the front drive shaft (between the transfer case and the front differential) by hand. If that won't move there may be a problem in the transfer case or the front differential that's causing things to freeze up.

(3) I could see dropping the transfer case and opening it up to see why things won't move.

Please take these thoughts as some random musings. There is someone out there who is much more knowledgeable than I am on this issue. I'm sorry I can't be more help.

Juan

Kamey16

Thanks for the reply Juan, I was afraid it might be internal to the xcase. I was wondering if the switch on the xcase worked like a lockout meaning the xcase wouldn't shift to 4wd w/o the front diff being engaged first. As I understand it now, it is nothing other than a switch for the 4wd indicator light. The xcase should always shift when the vehicle is stopped. Is this true?
Thanks, Ben

juandelnorte

Yes, when the vehicle is stopped there should be nothing preventing the transfer case from being shifted from 2H into 4H. There is no lockout. It sounds like something's either frozen inside the case, or the gears are not meshing properly.

Fortunately, the transfer case isn't that difficult to drop. Just make sure you mark the flanges on the drive shafts before you unbolt them. That way you can realign them the way they were previously. If the transfer case has serious problems, it might be easier to find a replacement at a junker and drop it in.

Best wishes,
Juan

Kamey16

Thanks for the information Juan!