4x4 help

[90 t4r]

ok so needless to say i found out that my 4wd isnt working after getting stuck and trying to use it, and having to be winched out. i have a 90 toyota 4runner v6, i thought it was working because i can feel the transfer case engage because when i put it in 4lo it crawls real slow but apparently either the front diff or something is preventing it from engaging, i really want to get this fixed so that my 4x4 is not actually a 4x2 and so i can go out and play in some mud.

 

[Hyde802]

Auto or manual hubs?

If its Auto, my guess is that you have a vacuum leak.

Get in your truck and start it up. Put it in 4lo and drive forward about 10 feet. Now, leave the truck in 4lo, shut it off and climb under it, can you spin the front drive shaft by hand? How about the cvs?

Edit: Just went through your pictures. Looks like you have auto hubs? Yes?

If you cant turn the drive shaft, chances are the slide collar in the front diff isnt moving due to a vacuum leak.

 

[fourwd1]

Auto or manual hubs?

If its Auto, my guess is that you have a vacuum leak.

Neither auto nor manual hubs use vacuum.

The ADD 4WD system does use vacuum to lock/unlock the front axle, but it does not use hubs at all. The wheels are permanently connected to the axle shafts via drive flanges (unless a previous owner has modified the vehicle).

A 90 most likely has the ADD system, and a bad Vacuum Switching Valve is likely if 4LO provides the gear reduction but the front end does not lock.

 

[90 t4r]

yes it does have the ADD system and i checked all of my vacuum lines and they are all connected and dont seem to be leaking now as for the vsv is there any trick to testing those or is it a replace and c if it works, i googled it and all i found were testing vsv on newer models dealing with a evap trouble code.

 

[Hyde802]

ADD stands for automatic disconnecting differential, so they are referred to as auto hubs all over the place. But I agree, technically wrong term.

Back on topic, You need to pressure test the vacuum lines to check for leaks and dry rot along the way, not just check they are connected.

Ive never owned an ADD before (not working anyway, mines locked "on") But I think you should be able to test the shift fork by blowing air (compressed?) into one of the tubes. Should be able to hear the collar moving.

 

[90 t4r]

yea ik they are not leaking cuz when i did my rebuild i carefully replaced all my lines. now when u say blow compressed air into the tube which tube are you talking about the vsv or the lines that run to the front diff?

 

[Hyde802]

The 2 lines coming out the diff. One should push the fork, one should pull it. Try just blowing into it, compressed air might hurt it.

But like I said, ive never owned a opperating ADD diff. Some one else might be able to shed a bit more light on it.

 

[90 t4r]

ok so try blowing into the vacuum hoses coming out of the diff and c if it goes into 4wd? should it stay in 4wd when i quit blowing or will it go out, and thanks for the help btw. i just wanna get this working so i dont get stuck again

 

[fourwd1]

ADD stands for automatic disconnecting differential, so they are referred to as auto hubs all over the place. But I agree, technically wrong term.

Right, Toyota has had manual hubs and auto hubs on the standard (non-ADD ) front axles.
ADD axles have NO hubs (they have drive flanges)
Many people do confuse ADD system with Auto hubs, which is incorrect.