DoubleSea

I have recently purchased a 1994 4runner 4wd 5speed with the 3.0 V6 for my son. It appears to be a good vehicle with only a couple of minor issues. One of the issues that's driving me crazy is the 4WD doesn't work. When I shift the manual shifter into 4H, nothing happens. The light on the dash doesn't illuminate, and it does not appear to be in 4WD. After doing a little research, I tried swapping the vacuum lines at the VSVs to activate the ADD system. That appeared to engage the 4WD, but still no light on the dash. To verify, I put the truck on a lift. With the vacuum lines swapped, if I shift into 4H, the drivers side front wheel engages, but the passenger side wheel does not. The passenger wheel appears to be trying to engage, but it doesn't. I'm not a great trouble-shooter of electrical problems. ANY help would be greatly appreciated.

muddpigg

iTrader: (1)

I’m confused by your post.

Light on dash may be burned out. Mines been out for a while. 4wd still works just no light.

the ADD is prone to problems. Is it a 5spd or auto (on my phone so can’t scroll up to reread). When transfer case is in 4wd and front tires are lifted off ground can you turn driveshaft by hand? When you turn one of the tires by hand what does the other tire do?

DoubleSea

5 speed. I'll have to lift the truck again tomorrow. Like I said, with the vacuum lines switched at the VSVs, it feels like it will go into 4wd. I thought this because I could feel the truck "binding" on the asphalt in tight turns. To verify, I put the truck on a lift and discovered that with the vacuum lines swapped, the front drivers side wheel will engage, but the front passenger side wheel will not. With the vacuum lines returned to their original position, neither front wheel will engage.

muddpigg

iTrader: (1)

So ADD is a sleeve that only “engages/disengages” on driverside axleshaft. Makes it more streetable. Can’t remember if you have drive flanges or auto locking hubs. Might be some info on the faqs sticky with more info on ADD. Some manually put sleeve in locked position and install locking hubs, other replace drivers side alxe housing and shaft from earlier IFS to completely remove ADD.

Chock rear tires (both front and rear directions), put truck in neutral, put in 4wd, have truck running (need vacuum, could use vacuum pump) raise driverside front tire. You should not be able to rotate tire if ADD is engaging.

Google or Youtube “open differential” for an explanation of its operation

Pretty sure a later model guy will chime in.

RJR

I wouldn't call ADD a "sleaze"; it's actually a pretty solid system that provides 90% of the function of manual hubs w/o having to get out of the vehicle. It does require some maintenance, esp on 25 year-old vehicles, however.

The '94 has drive plates, which means the front wheels are permanently locked to the CV shafts. The ADD is engaged by a switch on the transfer case, which switches the VSV's and pulls the ADD into gear. When the ADD actually slides into the locked position, the green light should come on.

Do the following tests:
- engine OFF, ignition ON (not accessory). Move tcase lever between 2hi and 4hi. You should hear a relay click under the dash. If not, the tcase switch is probably not working or the wiring is broken.
- If the relay clicks, now raise the hood, stick your head out the window, and again move the tcase lever (may need a helper for this). Listen for the VSV's on the passenger fender clicking. If they don't click, you need to trouble shoot the circuit between the under dash relay and the VSV's.
- If all that checks out, start the engine. Set ebrake, and with truck in neutral have helper move tcase lever from 2hi to 4hi while checking the vacuum at the VSV's. The port with active vacuum should change from one VSV to the other as the tcase lever is moved.

If all that checks out, raise the front of the vehicle, chock it good with ebrake set, start the engine with tranny in neutral, and move the tcase lever from 2h to 4h. Try rotating each of the front wheels as you do that, paying close attention to the front drive shaft rotation (or lack thereof) as well.

I've attached the wiring diagram for the ADD system, so you can see how it is supposed to work.

muddpigg

iTrader: (1)

Meant “sleeve not sleaze” thanks will correct

DoubleSea

Thank you both for the responses. RJR, I did as you described. With the key on, and the engine not running, I shifted the four-wheel-drive shifter from 2H to 4H and back again with no click coming from the relay. Even put my hand on the relay while shifing back-and-forth to see if I could feel anything. Nothing. Took relay off and a friend tested it for me. He said it’s good. So, I’m assuming that my problem possibly lies with the switch at the transfer case? Or the wiring between the two? I Crawled under the truck and I see two switches at the transfer case. One switch where the rear driveshaft comes into the transfer case. Another switch above that, kind of on top of the transfer case. Not sure which switch is the right one.

RJR

It's the top one. It detects the shift rails moving, which are on top of the tcase. The other one isn't a switch, it's your speed detector for the speedometer.

Muddpigg, sorry about the "sleaze/sleeve" misunderstanding. What with auto correct on everything these days, I find I have to read my posts over at least twice to catch all of the "edits" my computer gratuitously makes for me.

Kolton5543

Definitely sounds like the switch. That switch sends a ground signal to the relay to switch the VSVs and a sends a ground to the add detection switch. From there it goes to the 4wd lamp. If you have it in 4wd and switched the vacuum lines and its definitely in 4wd then its a problem with that particular circuit. Unplug the transfer case switch and jump it with a paper clip. If things start working then replace the switch. If not then check for a break in the circuit and check the gorunds.

DoubleSea

Thanks to all who have replied. So, I jumped out the transfer case switch and everything seems to be working as it supposed to. Four-wheel-drive lamp comes on – and I can hear the VSV clicking . Now, the question is, how in the world do I get that switch out without dropping the transfer case?

muddpigg

iTrader: (1)

No worries, it’s a pain to edit on the IPhone is text is larger than dialog box. I should put a disclaimer on my sig block but can’t seem to get that to work. Probably ought fire up laptop and give that a try.

RJR

You might be able to get enough room to remove the switch by unbolting the rear crossmember that holds the tcase and dropping it down carefully on a jack. The whole engine and transmission assembly will pivot as a unit on the front engine mounts. It should come down 4 inches or so before things up front get into trouble. You'll have to watch for fan clearance and wire and hose stresses, but I think it can be done. The FSM recommends doing that to get better access to the upper bell housing bolts when dropping the transmission. Might have to remove the fan shroud. You might also have to go inside and remove the shifter levers before you do this, but that's fairly straightforward.

Alternatively, you could just wire the relay under the dash to a toggle switch on the dash and switch the ADD that way. That would give you the added feature of 2wd lo-range, since with the ADD unlocked, the front wheels will be freewheeling even with the tcase in 4-lo. 2wd lo range can be handy on tight trails for manuevering around sharp corners, particularly on "slick" rock (which is NOT slick.) Also, leaving the ADD engaged during snowy/icy conditions makes it even easier to shift back and forth between 2wd and 4wd on the fly, since everything up front is already turning and nothing has to be dragged up to speed by the synchros in the tcase.

DoubleSea

I got the switch out this morning. Didn’t have to lower anything. The boxed end of an 1 1/16” combination wrench cut off to about 6” works perfectly! Now, all I have to do order the new switch. Do y’all have a preferred vendor for parts? Thanks so much to all that have taken the time to reply. This site is a very valuable resource. Thanks, again. Now on to my next issue. Maybe this should go in a new tread, but does 12-13 mpg around town sound right?

RJR

Rock Auto is good if they have it. Or try ToyotaPartsOverstock.com. That's an actual Toyota dealer in Lakeland, Florida, with an online presence and good prices.

scope103

Does it look like this?
https://www.ebay.com/itm/8422235060-...-/182321898936
(United Arab Emirates??? Hey, we live in a global economy.)

Like RJR, I use https://parts.lakelandtoyota.com/showAssembly.aspx?ukey_assembly=496293&ukey_make=1 060&ukey_model=15426&modelYear=1994&ukey_category= 21647&ukey_driveLine=6750&ukey_trimLevel=18205&sea rchString=transfer Lakeland Toyota as my go-to for dealer parts (I have ordered from them; all was good). Note that there are two possible switches; this might call for a telephone contact.

Sometimes you can get the part number from the website, and google search just on the number. Often, eBay sellers are no cheaper than the dealer, so I stick with the dealer. But every now and then you can get an interesting hit in the Middle East.