I don't drive the T a Whole lot since picking up a TDI Jetta (nearly ALL of our mileage is on-road to and from the nearest town, which is a 300 mile round trip drive), and I don't need 4WD very often while in the T ~ mostly just in the winter when going skiing or in the freak snow storm. It seems that every time the truck goes for awhile (time frame, not mileage) without getting into 4WD, it doesn't Want to do 4WD. I'll pull the lever and nothing will happen ~ even if I stop and put it into 4-low, it doesn't act like it's in 4WD and the idiot lite on the dash never comes on. Now, if I play with it for awhile (maybe an hour of actual time in the truck), it'll start clicking behind the dash (like when the idiot light comes on), but without the light and seemingly without 4WD. Play with it a little more and eventually it'll click once, the light will come on and I'll get a slight buck if I'm moving and the 4WD is very much on (most my testing is on dry pavement, so I get a little binding going arround corners and such).

Anyone else have the problem? (I'm guessing no cause everyone else actually USES their truck <img src="/forums/images/graemlins/rolleyes.gif" alt="" /> ) Does the in-cab lever work a linkage that may be binding? Or is it just an electronic switch that may have corrosion? Any other thoughts/ideas? I don't have a manual, and don't really know much about 4x4's in general....

Thanks

Brian

Well I'm by no means the expert but when my 4WD indicator went out it was a vacuum line. This particular line was at the top of the engine and did not directly connect to the ADD actuator. The symptom was the same as yours. Could pull the TC lever and felt the appropriate notch but definitely no 4WD. A friend, who runs an import repair shop, said it was a line that attached to a "vacuum reservoir" which was letting the vacuum fail and caused the ADD actuator to also fail its function. I've also read here that there is another line at the actuator that can get pinched off by mud accumulation and fail similarly. Brew <img src="/forums/images/graemlins/cheers.gif" alt="" />

bmccoy,

There are generally two things that happen when you put your truck in 4x4. First, the "lever" you are pulling on in the truck is directly attached to the transfer case and shifts the transfer case into 4x4 to send power to the front drive shaft. Second, there are two vacuum lines (as mentioned previously) that actuate the front hub system to lock the wheels onto the front axle. From what I understant, the light on the dash will not come on until these front hubs are locked in. It could be as simple as a small vacuum leak.

My vacuum lines are on the passenger side on the engine and run to the inner fender well where tehre are switching soleniods and then the lines run down to the front axle. Check there first for a vacuum leak.

Good Luck

So it's a direct linkage and as long as the lever moves all the way into place (and there's nothing else funny going on), the front drive shafts should be turning. Is that right? Then since I have manual Asian hubs, it would be in 4wd even if the light doesn't come on. Sure doesn't Feel like that.

And I'm not sure if I'd made this clear before, but once I spend the time fiddling with the lever in the truck and get things working, it then works 100% fine till I go and don't use it for a month (it's be switching in and out of 4wd as it should the past day, and I remember it doing so for well over a week 2 different times last winter when I was doing a lot of mountain driving).

Thanks for the info ~ I have a better idea of what to look for now.

Since no one has mentioned it, and I have had this issue several times. The first time I had an issue with it, I replaced the switch on the side of the transfer case and that took care of it. The switch is what activates the solenoids that shift the fork in the front diff and enables the front axle to be engaged. I would suggest checking the switch with a multi-meter. IT is located where it can get all kinds of gunk into the wiring connector and not get a good signal to allow the solenoids to work. The last time mine acted up, which was last year, I took the wiring connector apart, cleaned each side of the connector with electrical contact cleaner and added some "Di-electric grease" to each side, then reconnected the wires. It worked flawlessy the rest of last year. I think that is why Toyota recommends that you engage the transfer case and 4 wheel drive at least once a month. Which reminds me that maybe I should check mine out, since I haven't for quite some time.

One more item,is the fact there is also another switch on the front differential. This switch is the one that actually causes the light on the dash to come on, but I have never had a problem with that one. I have checked the operation of it though and it has always worked, as long as the fork was shifting, it was OK.

I'll see if I can find the article about disconnecting the ADD feature and post a link. Here it is: http://www.4x4wire.com/toyota/tech/add/
Another link that might help would be the one that has the '93 Toy Truck manual on it. It would give a breakdown of the ADD system and should show the location of all of the components. All T's should have the ADD system that was in use on the runners and small trucks.
Here's the link for the FSM for '93 Toyota truck: http://personal.utulsa.edu/~nathan-buchanan/93fsm/

If you disconnect the ADD, then all you have to do is lock the hubs (if you have lock-out hubs) and pull the lever back.

Not quite... read carefully what he said. It is a direct linkage to the front driveshaft, not to everything else. Your Automatic Disconnecting Differential (ADD) uses vacuum pressure that actuates the front differentials drive of the front axles. The only thing your manual hubs allow you to do is unlock the hub from the front axles.

For 4x4 to work the following must be in place:
1) Lock your hubs. Trying 4wd without locking the hubs is ill-advised. Before you put Aisin's on, you had a flange plate that essentially was a permanently locked hub
2) Pull your 4wd shifter. This engages the transfer case to the front driveshaft.
3) Vacuum pressure engages the front axles (this is done via a switch connected to your shift lever). If for some reason you are not getting vacuum pressure then the light doesn't come on and you don't truly have 4x4.

Does that make sense? I'm not totally sure why fussing with the 4wd shifter finally makes it work for you. But for some reason you aren't getting vacuum actuation (either because of a vaccum leak, switch malfunction, etc.)

Good luck,
Joel

Thanks Bill and Joel - I've got a better understanding of what needs to happen for 4WD now. I'm just going to crawl arround the truck as soon as it quits this freaking 110+ daily weather and see what I can figgure out. Sounds like maybe that electrical switch is a pretty good suspect (would seem to be more of an intermitant electrical issue than a vacuum issue ~ which are Rarely intermitant like this).

I'll post back when I figgure it out. Thanks again guys.

I had the same problem when I first got my truck a couple of years ago. You move the lever to 4WD and it was slow to engage, you might have to drive several hundred yards before the 4WD light came on. I did two things that seemed to fix it, as I've not had any trouble with it since, but I'm not exactly sure which one was the fix as I did them both at the same time. First, I unplugged and replugged the connectors. If it was an electrical contact problem, this may have fixed it. Second, I replaced the front differential fluid with Mobil 1 (I think it's 75W-90). The old fluid looked thicker than what should have been in there, and maybe that was making it engage slow, or maybe the synthetic just works better if you aren't in the habit of using 4WD a lot. It's been working greater ever since.

actually, that switch is tied to the shift rails internal to the tcase, not in the shift lever.

Okay, I was out of town for a week so the truck sat again. This morning I took it out to drop off some mail and tried 4WD again. I heard a LOT of clicking (that I would link to that of a relay), the dash light clicked on and off close to 2 dozen times and then it stayed on and fussed no more. I kicked it in and out about 3 more times over 7 miles and it worked as it should.

I'm going to get under the truck soon... though probably after the monsoon season (raining a lot up here right now).