*searched* 4x4 wont engage ADD
 

93 22re 5spd and all of a sudden my 4 wheel drive doesn't work. Nothing has been done to the truck to screw with the vacum hoses or wiring, it just didnt work one day. The relay behind the instrument panel clicks and the solenoids also make a sound and you can hear/feel the vacuum as someone moves the shifter back and fourth from 2wd to 4wd. You can also feel this vacuum down on the differential when the hoses are removed. Now im not entirely sure, i just had someone in the cab moving the stick back and fourth but it seemed like i had vacuum on both lines when the stick was in 4wd and no vacuum on either when it was in 2wd, i dont know if this is how its supposed to work. Also i dont know how much vacuum there is supposed to be but you can barely hear the hiss when the motor is on and you really have to try and notice its "pull" on your finger. This is the case at both the ADD solenoids on the wheel well and at the diff, so it isnt a bad line going from the solenoids to the diff. Any ideas?

Sounds like the solenoids to me. You could get a vacuum testing gun and hook it up to the actuator. Then pump it up, and see if it moves. That way you will be able to eliminate that as the problem. Then you could look towards the solenoid.

Or get some manual hubs and bypass it. :D I'm not against ADD while its working but I wouldn't spend any money to keep it working.

I am going to put manual hubs on eventually but mine are on an axle that is buried in snow and its pretty cold out now so i was hoping it would just be a simple fix but if it isnt ill just have to get to work. Ive read an article on toyotaoffroad.com about add and it seems to me that when in two wheel drive vacuum should be going to one side of the actuator and in 4wd vacuum should be going to the other side. Is this true? if it is true and i have vacuum to both sides in 4wd only is does this mean that one of the solenoids is gone?

http://toyota.off-road.com/toyota/ar....jsp?id=399612

The bottom of this article might be able to answer your questions as to which side of the actuator does it. I'm with Mt Goat. I replaced my hubs and ran a vacuum line down to the actuator so the ADD is permanently locked. Well, unless a vacuum line gets a leak, which happened the other week, so I simply traced down the problem and replaced the hose.

you say you get vacuum on both lines in 4WD, and none in 2WD? Thats not how it should work. I just spent the last 3 days under my truck of the same vintage trying to solve my 4WD issues before realizing my lines where switched. You should have one line pulling vacuum in 2WD, and the other line pulling vacuum in 4WD. At the front diff where the vacuum lines go in, the one closest to the drivers side should have vacuum in 2WD, and the one closest to the passenger side should have vacuum in 4WD. Why you are getting all or nothing, I dont know. It sounds like the control (whether the ADD relay or 4wd computer or whatnot) is screwed up, but I wouldnt be able to tell you what....

good luck with that

I would suspect what ever controls the VSV valves on the drivers side wheel well is the culprit. I think there is a controller module under the dash that does that work. I had a similar problem with a Tacoma that drove me crazy so I vaguely remember all the key components of the system. So, if working and then suddenly not working, assuming all vacuum components are good, sounds electrical. All fuses checked and good?

Hope this helps. I would go to the service manual for your ride, and download the wiring circuit. There is a link on this web site for the manuals best I remember.

my 4runner did the same thing last week, the add takes hardly no pressure to engage. as i could engage mine with my mouth this afternoon. if you have vacume then vsv could be bad, switch the vac lines if that dont help it is not the vsv. pull the add when you can and see if it functions. power brake the truck see if the front drive shaft is spinning, look for your cv joints if one is turning it is either the hub or the cv joint, if not and the add is functional sounds like axel shaft failure( i broke a axel shaft i think, i worked till my hands froze then gave up) i'll pull the front ifs third when i can to crack it open and really see