fsbi2

Hi there, I've got a 4WD issue.
I drive a '89 pickup (V6) with ADD hubs and manual trans.
So I just replaced my CVs the other day and afterward I tested the 4WD and everything was working fine. Then the next day I had it in 4WD and I went over some rough bumps and the 4WD light went off. It took me a few tries but it finally clicked back in and the light came back on.
Then today I go to throw in into 4WD and I get the "click" behind the dash but no light comes on and therefore the wheels don't engage.
My first thought is that my vacuum tubes are either busted or coming loose. Really don't know much about my ADD system though...
Any Ideas?

Thanks.

scope103

My first thought too. Did you look at them before making this post?

fsbi2

Hah! I would have except it was -30 out this morning and I was late for work. I'll try to have a look today if I get a chance but I'm not really sure what I'm looking for. Are they just tubes coming from the differential and running up to the soleniods?
Thanks...

scope103

Mostly. Underneath are two vacuum tubes. They come up to the rt hand apron (inside of fender) to two vacuum switching valves. The valves get the vacuum from the plenum, paralleled to a reservoir which is on the wheel side of the fender (so there is a vacuum line through the apron.)

Philbert

iTrader: (2)

are you sure you're not engaging 4WD or is the light just not coming on? Could be your 4WD indicator wiring got jarred loose? that happened to me - thought I had a burned out dash bulb but the harness was fubared and not completing the circuit when I was actually in 4WD.

Stuwy123

iTrader: (1)

There are two circuits that make the 4WD dash light come on.
The first is the closed circuit from the front diff switch. The small plug on the front of the front diff. There is a plug that connects the diff to the engine harness. If this is disconnected at the plug or the sensor, the light doesn't work.
The second circuit is the same sort of switch on the transfer case. There's a plug on the harness. Check for breaks in either circuit.

Are the vacuum lines connected? Check at the diff and at the actuator on the passenger side of the engine bay beside the fuse box. Just follow the lines up from the diff.

4wd will engage even with the light on in the dash. Easy way to find out is find an icy patch next to drive pavement. Rear wheels on the ice and front on the dry. Put it in 4wd and gas it. If you move forward, then you have 4wd and no light. If no forward movement, you're not in 4wd. Check the front diff vacuum actuator and vacuum lines.

fsbi2

Ok, here is an update:
I checked the vacuum lines for anything obvious. I don't think I’d be able to see any hair line cracks but both hoses are attached and the actuator looks intact for the most part.
So the 4WD still wasn't working until just a few weeks ago I happened to be going about 50 with the shifter in the 4H position. All of sudden I hear a “tick” “tick-tick” sound coming from the steering column, right near the turn signal area. It does this for a few minutes and then, as I slow down, my 4WD light comes back on! Sure enough, my 4WD works great. I can engage and dis-engage it just fine.
So it worked well for a few weeks and then this last weekend I tried it and its not working again. Same thing with no 4WD light or “click” sound when you move the shifter. I tried driving with the shifter in 4H again to see if that might make it start working again, but no luck so far.
I happen to have a new actuator for this truck so I thought I’d try throwing that on first to see if it made a difference. I don’t have any other good ideas other than double checking the vacuum lines and making sure the diff fluid level is good. Any ideas?

scope103

Rather than just looking at the vacuum lines, pull each off to feel for vacuum when someone switches between 2wd and 4hi. If no vacuum there (or it doesn't switch), trace the lines back to the two VSVs and check to see if they are getting vacuum.

Just be systematic and you will locate the source of the problem. http://personal.utulsa.edu/~nathan-b...26addcontr.pdf Fixing the problem might take a little more, but it sure beats driving down the road with it left in 4hi just to see if something happens.

Gevo

My 4WD engaging issues are due to the relay under the dash (this is the tick tick tick sound). I would do as scope said, but since you seem to have a few symptoms like mine just have someone shift to 4WD while you are at the two VSV's in the hood and have the hoses unplugged, check that you feel a vacuum change from one VSV to the other, if so then your relay is working and your problem is some other part. If no switching happens then your relay and/or something in the circuit is bad.

Easy way to test if mechanically everything is working is to jack up the front, turn one tire and see if the differential is engaged (if it is you will see the other tire spinning AND the drive shaft from the transfer case to the front diff). Then, pull the two hoses from the two VSVS that go down to the actuator and apply vacuum (mine works by me just sucking on them) to one, repeat the wheel spinning test, and the other and again repeat wheel spinning test. That's what I did and i narrowed my problem down to the relay (aka fuel pump relay) which is a badass expensive relay and i hate toyota for it!


PS: I wrote this fast so hope it makes sense

fsbi2

I'm revisiting this issue again as the temperature recently dropped and my 4WD stopped working again. It was working all summer long and then as soon as snow started falling it started acting up again...
I'm considering following this guy's instructions for bypassing the vacuum system entirely and having the sleeve inside the differential permanently locked : http://www.4x4wire.com/toyota/tech/add/
Any disadvantages to going this route?

Thanks

RJR

The only disadvantage is that the 4wd system (driveshaft, differential, ring and pinion) will be turning all the time, even in 2wd (unless you also add manual hubs). No real harm in that except that it causes more drag and a slight loss of fuel economy.

Since the problem appears to be temperature related, it sounds to me like you have an actuator that is reluctant to work when it gets cold. Could be your gear oil is turning to glue at -30F. I'd pull the cover off the ADD actuator mechanism on the diff and check for stiffness in the mechanism. Maybe you just need to drain the diff and refill it with some synthetic gear oil that will not get so stiff at low temperatures.

fsbi2

Thanks Ron. That's a good thought. I remember checking the gear oil level last winter but I never pulled the actuator off to fiddle with the mechanism. I'll give that a try.

I spent some time last winter checking the vacuum situation at the solenoids. I think I remember the suction not switching in the lines when 4Hi was engaged at the shifter. I need to check that again but if that was the case then the problem probably isn't the actuator right?

As far as getting rid of the ADD system altogether, I would definitely prefer to not have the driveshaft and differential always spinning. I live in a very cold climate and that seems like asking for trouble.
How hard is it to install manual locking hubs? Which brand is recommended?

Thanks!

RJR

That would be correct.

Manual hub installation is pretty straightforward - you don't even have to jack up the vehicle. There are multiple articles about it on the web, I think 4x4wire has a good writeup. You can buy new Warns, but web wisdom says that the Aisins (OEM brand) are the best, and they are readily available on ebay for around $100 per set. That's where I got mine. Just make sure you get the right ones - I think there are different numbers of splines depending on the model year.

axs4all

This happened to me where it all started with my 4WD light indicator not turning on. I removed the ADD relay and checked for continuity and then checked that it engaged when connected to my battery (pins 2 and 6). I also checked the Ohms on the vacuum solenoids, connected them to my battery to make sure one sucked air and one blew out air, and also checked the continuity on the transfer case switch. Everything checked out as they were supposed to so I figured that it'd have to be some type of wiring issue. Sure enough, the wire connector coming out of the differential to the engine harness was loose. The connector is not the one to the transfer switch by the ADD but rather above the differential in line with where the 4WD shifter is located inside the cab. I removed it, put some bulb grease and immediately heard the ADD relay engage and then saw the 4WD indicator light come on. Of course, I took it for a test ride and could immediately notice the 4WD working on the pavement when making a turn. Hope this helps others!