Guys,

Sorry this post belongs in this forum. I posted it in the runner pick up forum accidently.

Snow is here and I've put off fixing my 4WD long enough! My 91 V6 Auto with ADD will not drive the front wheels when shifted into 4 HI or 4 low. It will shift into low gear when shifted into 4 Low but only in 2 wheel. So the hi low clutch is functioning. The 4WD dash light does come on when shifted into 4, so the ADD is locking.

Things that check out ok:

ADD
Transfer Chain
Transfer Case oil pump
Transfer clutch looks ok

Since the ADD is working, the ADD transfer pressure switch must be seeing hyd. press. So does this mean hyd. press. is getting to the transfer clutch?

I'm going to put some low press. compressed air into the hyd. vlave control box to trace the flow and see if it is obstructed somehow.

Is the #4 Solenoid only a high speed safety lockout for the 4 low?

Anything else I should check?

Great Thanks to anyone who can help!

Steve

 

Seems like the transfer switch body may have been clogged. The thing looks like a complicated rat maze of hydraulic channels inside. I ran some air through the transfer port that runs to the transfer clutch and moved the plunger that swithes the path of the hydraulic pressure. It didn't switch. Took it apart and didn't see any debris but did find a small amount of sludge. The little filters were clean. Put it back together and tried it again and it switched. So i'm hoping this was the problem.

We'll see if it works. I'm going to leave the front drive axle disconnected and put the rear end on stands. this way I can check to see if the front drive flange turns when in four wheel. I can also try to turn the front diff flange by hand to make sure it's locking.

This truck is the biggest PITA to work on. Nothing is easy! Come spring she's getting a GM 6.2 Diesel and a 700R4. I'm tired of the thing not working. I'm tried of difficult repairs. I'm tired of not having any power and bad fuel economy when it is working.

Hope this post helps anyone who runs into similar difficulties

Steve

 

If you have not found these pages:
- http://www.off-road.com/toyota/tech/add/index.htm
- http://www.4x4wire.com/toyota/tech/add/

Check them out.