4wd Not Engaging

elks · #1 (**permalink**) 09-11-2007, 11:01 PM

I posted up in teh 1st gen, somebody siggested to post here. So here it goes.

My 4wd is not engaging in my 01 Tundra. The transfer case switching in, but hte front diff is not catching. I am hoping it is just a bad connection some place, but when I checked teh connection on the Add unit it looked good. I used the 4wd a week earlier while hunting everything worked as expected. THis last weekend I got in a major twist. Rear tire about 3 feet in the air at full flex tires stuffed. Hit the 4wd button and nothing. Again t case iengaged, but not the diff. So is there a way to check the power to the add unit? Does it sound like the Add is out? What options do I have? Is there a cheap way to up grade to manual hub? Any help is greatly appriciated. I use this truck about 70% Off road 30 % pavement (usually geting to the dirt). The last few weeks have been hunting the roads are really wash boarded and I am hoping somehting got rattled loose.

Thanks again for the help.

jjc · #2 (**permalink**) 09-12-2007, 07:12 AM

I would pull the ADD and check to see if it's actually moving when you hit the button, better yet......pull it and make sure the shifting fork has not broke.

DevinSixtySeven · #3 (**permalink**) 09-12-2007, 11:21 AM

Rob-

x2, and check to see if your 01 ADD unit has a vacuum line like the 00 trucks. If the line is broken somewhere, the shift fork will not engage in the front diff. Also, if the line is compromised, it'll take in water over time and rust out the ADD unit from the inside.

Sorry to hear about this, bow hunting sounds like a helluva lot more fun than tearing in to your truck!

-Sean

elks · #4 (**permalink**) 09-12-2007, 02:25 PM

OK it does has a rubber line running from the top of unit. But I assumed it was a vent line like a diff has. But it could be a vacuum line. At any rate the line was cut about 8 inches up from the diff. That could be the issue. Does anyone know for sure if the add unit on an 01 runs off of vacuum?

Also isthere any way to tell without taking the unit off? Does taking the unit off require droping the diff? Or can I sneak it out while diff is in place?

Thanks again for the help. I would assume that if the fork was out or that something was broken I could here it trying to click in. AS of now when 4wd is engaged nothing happens at all.

jjc · #5 (**permalink**) 09-13-2007, 01:08 PM

Quote:

Originally Posted by elks

OK it does has a rubber line running from the top of unit. But I assumed it was a vent line like a diff has. But it could be a vacuum line. At any rate the line was cut about 8 inches up from the diff. That could be the issue. Does anyone know for sure if the add unit on an 01 runs off of vacuum?

Also isthere any way to tell without taking the unit off? Does taking the unit off require droping the diff? Or can I sneak it out while diff is in place?

Thanks again for the help. I would assume that if the fork was out or that something was broken I could here it trying to click in. AS of now when 4wd is engaged nothing happens at all.

I believe its vacuum and electric..... Whichever it is, the hose needs to be fixed and that's a good place to start troubleshooting.

DevinSixtySeven · #6 (**permalink**) 09-13-2007, 01:56 PM

The breather line is extended to the engine compartment, attached to the driver's side skirt inboard of the upper control arm. Look for two small silver caps. If that's the same hose type you're seeing, reconnect the breather line after you've solved the current problem.

The vacuum line is much smaller, maybe a hair over 0.125", certainly no larger than 0.25".

elks · #7 (**permalink**) 09-14-2007, 03:52 PM

OK I need some more help. Does anyone know where the Vacuum Lines connects at both ends? I am pretty the last shop I had the vehicle at may have swapped the 2. As of right now I only have one breather hoes hooked up and it is the larger one from the Pumpkin area on the Diff. The second line that is not connected comes off the rear of the ADD unit and is pretty small. It is taped up to the the wires that plug into the add unit. Any idea if this is a Vacuum line or a breather line. I hate newer vehicles cause you have no access at all to good diagrams.

If somone has a pick of their unmolested add unit hukk up that might help. Of if you can tell me where the vacuum line runs would be awesome. I searched all over and nothing on the web.

Thanks again

elks · #8 (**permalink**) 09-14-2007, 04:08 PM

Ok something else to ponder about. When I first got my truck if the 4wd did not engage there was a beep sound to assist. Of if I tried shift to 4 low in gear etc. That sound is gone. Does that have anything to di with it? I am heading hunting in about an hour and am trying every last second thing I can think of.

Thanks again elks. I have convinced myself that I have no vacuum lines. Just one breather line. Unless some says different I think the vacuum issue is not possible.

Tundra_Hick · #9 (**permalink**) 09-14-2007, 05:55 PM

Since your 4x4 won't be working, remember to take some rope with you.

Wrap the rope around the tires, over the tread, then through the holes in the rim, around and around, until the tire resembles a tractor tire.

It might not be 4 wheel drive, but that will get you out if you get stuck.

Jwitz · #10 (**permalink**) 09-15-2007, 12:41 PM

I wish I knew for my own purposes, but I have some off the top of my head sugesstions. You could turn on acc (not engine running) and have someone hit the 4wd button and find out if any noise is coming from your add unit. If not I would probably pull the connector and attach a light to the connector (this would be good if you had the toyota wiring diagram). If the connector has no positive signal, then maybe a fuse or relay has gone. if it's okay, then its certainly possible that the add unit has gone. I would say if the dealership wants more than 1500 to replace it, you would do better to buy the manual hub kit and rig the add to lock (which I have no idea how to do...) sorry to be so vauge, but I really have no idea, simply suggusting what I would do in your situation...

elks · #11 (**permalink**) 09-17-2007, 07:09 PM

OK so some how I got it working again, but have no idea how. I could not find anywhere on teh ADD unit where the vacuum line exist. The only line comming out at all was the breather for the ADD unit. At this point I am convinced I do not have vacuum to it at all nor does it need it. I might be wrong??? I did notice a slight Transfer Case leak and found my fluid about a 1/2 quart or so low. I filled it up and then proceeded yo hit things with teh hammer for a bit and wiggle all teh wires I could find. I then went showered headed out hunting. Got about 4 miles from town decided to try it at a little speed. 4wd locked right in. I slowed down took it out. Over the weekend I engaged and disengaged it several times not needed, but just for practice. It went in and out each time with out an issue. I even tried it in a situation where it should not go in and the light flashed and thebeep was back? I have no idea what I did, but I would like to know the cause incase this happens this winter while out predator hunting in -20 degree weather and 2 foot of snow.

Any Ideas on what it might be? Is there a possible sensor in the Transfer case that would keep 4x4 from working if fluid is too low?

ANyone else have an idea where the issue maybe?

jjc · #12 (**permalink**) 09-18-2007, 12:01 PM

I'm pretty sure my ADD is electric only now that I think about it.

2kTundra · #13 (**permalink**) 02-11-2008, 04:16 PM

Okay, on Saturday I had the same situation as Elks. I went to the mountains to ride quads and when I got to some snow & ice, I went to engage the 4WD and had the same problems. The light kept blinking; I tried backing up, driving slowly forward, and putting it in nuetral w/no success. Then when I got home that night I tried it again and all of a sudden it worked fine. I have tried it several times since without any problems. What gives?

I had this problem with a 96 Z71 but once it stopped working it never worked untill I swapped the actuator on the front drive shaft. That one was all electric and had a silenoid that would warm up and pop out to engage the hubs.

My Tundra is a 2000 so is it a vacuum plus electric, vacuum only, or electric only? Also does anyone know if it is similar to what was on the Chevy? Thanks!

deadrise · #14 (**permalink**) 04-16-2008, 11:55 AM

I'm having the same problem too. Was working fine, had my transmission fluid changed, got down to the beach and it won't engage. Just blinks at me no matter what I do. I'm not saying it has anything to do with the tranny fluid change, but it was working before that.

I can hear the ADD or something clink/clunking down there, but no 4wd.
If the ADD is making a noise, could it still need replacing??

I've tried all the tricks, backing up, parking, turning on and off, etc.

Hopefully, someone's had the same problem and fixed it....please post what you found out.

Thanks

Cliffy1 · #15 (**permalink**) 04-17-2008, 09:37 AM

I'm not sure if I should even post this because I am a sales guy and not a mechanic. I did however, have a similar problem on my old generation Tundra. It was like the thing was unplugged at the transfer case. I took it to my service department and they told me some part needed replaced. It was under warranty so I said fine. I had them do a complete service on the truck on that day which included a transmission service and I think changing the the fluid in the transfer case.

They ordered the part and it took several days to get it. In the meantime, I checked the 4WD and it worked just fine. By doing nothing except changing fluids, the problem was gone. It continued to work until I sold it and I used the 4WD several times after this incident.

The truck had about 45K miles when this happened. I know this doesn't sound right, but if this happens to you, change the fluids first, then look at other things.