Stuck in 2H, won't shift into 4H/4L any more

I've been scouring the threads looking for a solution and I think I'm getting a better idea about what's going on:

I have a '98 3.4, with a manual transfer case/gear box/whatever. No push buttons. It's 20-below and yesterday, 4-wheel drive worked. Today, not any more. I'm sensing that since it's a 15 year old truck, the vacuum hoses might be a tad word and/or disconnected, and I'll check that. But what else could it be? Does electricity play a part in engaging & disengaging the 4-wheel drive, like on the push-button shifters?

I have replaced both front axles 15K miles ago (last June) and I've hear NO grinding noises or anything out of the norm. Just abrupt failure to go into either 4H or 4L.

Does my truck also have a ADD? Is it electric? Would the oil level in a gearbox or transfer case affect it's ability to go into gear? I have less than 4 hours of daylight to get under the thing this weekend, and it's going to be cold this weekend. I'd like to have an idea what I'm looking for, so any suggestions are welcomed.

Thanks.

 

If your vac. lines are old & worn maybe check them all & I'd check into what kind of damage can occur when in sub zero climate, thats all i got for ya man sorry...

 

If there aren't any vacuum lines, theres a sensor that actually locks it in 4wd when you pull it into 4H your ADD motor could be shot. When I did my conversion I applied 12v and left it locked in and by passed the switch, but I know the switch activates the gear because I use it for my 4wd indicator light

 

This is from a 1996 repair manual.

 

Well THAT'S interesting! Thanks for that, Sin...I appreciate it.

I went out today and pulled off the skid plate and checked my front transfer case gear oil. It was low, and took more gear oil than I expected, about 3-4 oz. I got underneath and checked anything visible I could check. Wiggled a plug connector thing underneath where the gear shifter goes through the floor.

...And it goes back on again. After some quick, staccato clicks underneath the gear-shift, the 4x4 light came back on. I don't know if it's because I topped off the transfer case or whatever. But for now, it's working again.

 

I was working on a 2003 3RZ Tacoma before with a 4WD inop situation. I put it on jack stands, shifted the transfer case into 4HI, and let it idle in 1st gear. I went under the truck and gave the ADD actuator on the front diff a few taps with a plastic hammer and the 4WD worked. Those actuators are famous for sticking if you don't use 4WD a lot.



I used a regular hammer not a plastic one.

 

When mine was new it would hesitate going into 4hi and 4lo. Usually had to shift between D-N-R a few times. It only hesitates a little on 4lo now. I attribute this to wearing in from use. This probably doesn't help you, just letting you know what I experienced. I vote for the ADD actuator mentioned by rat107.

 

Interesting, Sin, that the repair manual troubleshooting chart doesn't even consider a problem with the vacuum lines. I would have thought it would have...

When I got inside and tried again with the selector lever and heard a series of audible fast clicks beneath the floorboard, I learned that there's an electrical connection possibility going on. Perhaps I should get in there with some dielectric grease and clean that connector up.

 

I'm not familiar with the issue, so I'm trying to get a better idea what's going on. When you say "won't shift into 4h/4l". You weren't able to physically shift the 4wd lever, or you could shift the lever, and nothing would engage?

I assume the numbers in each row point to what to check in that order?

There's an actuator that...does what? I've never heard of this. I always thought if you had a 4wd lever, it was 100% mechanically activated.
How can this be avoided? Smother the actuator in dielectric grease every couple years or something?

 

It's to engage the automatic disconnecting differential (ADD). The actuator is internal. That's why Toyota recommends that you drive in 4WD at least 10 miles per month to keep everything lubed up and functioning properly. They put that in the owner's manual.


http://www.off-road.com/trucks-4x4/...-disconnecting-differential-system-19259.html

 

Aside from checking the vacuum lines, you should definitely give this ^^^ a try. I've seen this "fix" many 4wd systems that were not engaging from either cold or lack of use.

 

The only way it is 100% manual is if you have a j-shift transfer case (no "4wd" button) and manual locking hubs. Most 1st gens have ADD (Automatic Differential Disconnect), which is what took the place of manual locking hubs. So although the transfer case may be manual, the ADD still has an actuator (electronics & vacuum) that needs to work properly to lock the hubs to be in 4wd.

 

Ahhh. This is starting to make more sense.
But ADD or Automatic Differential Disconnect implies that it only disconnects the diff, not engages it. Judging from the name, I wouldn't think it would cause a problem with lack ofengagement. or is it a bit of a misnomer?

 

ADD takes place of manually locking hubs. For instance if you put the transfer case in 4HI and don't lock the hubs you won't have 4WD. Same is the case with ADD. If the ADD doesn't engage you will not have 4WD even if the transfer case is in 4WD.

 

I just had this problem on my 96. Drained the TC and found chunks....no bueno...turns out the "stopper" sheared off. Apparently its not a common part and there are only 2 left in the country. Hopefully its not the same problem im having.

 

I've had that happen to me about 2 weeks ago. Now everyday I switch into 4H, and 4L atleast once daily to make sure that doesn't happen again. Once you get it fixed I suggest you do the same.

 

instead of posting another thread, what causes the shifter to become really hard to shift from 2hi to 4hi, while moving? I can only shift if im doing like 20 miles an hour. lame

 

The faster you're moving the harder it gets to shift, naturally. This is due to the fact that you are trying to get two different gears to mesh/ line up, while both moving at a decent speed. I'm assuming you have the j-shift style transfer case shifter, rather than the push button style, correct? I believe the push button style is the only true "shift on the fly" style in the first gens. Plus, you shouldn't be needing 4wd much if easily exceeding 20+ mph, but if you do, slow down/stop, shift, then ramble on.