Just got my new truck, but the 4wd doesnt seem to work. When you move the lever into 4wd, i can hear a relay clicking under the dash, the 4wd light on the dash will flash a few times, sometimes stay on for a few seconds, then go off. I deffinately dont have the front wheels turning. The truck is a 91 4runner 3.0 auto

 

check the vacuum lines http://www.4x4wire.com/toyota/tech/add/

 

With the ADD removal. Sounds very interesting and simple, but then are my cv's always going to be turning? From what I get from it, that when you remove the ADD system and clamp that fork into place, the front diff is always ingaged now, but the front drive shaft will not be turning until you engage the T-case correct?

This seems like such a simple thing, why would toyota have installed this ADD system?

 

You should be moving when you engage the 4wd.

 

Your CV's are alway turning now... unless you have manual hubs. What will change if you do that mod is that your front driveshaft will always be turning as well, even in 2WD, but it will be driven from the fact that the front wheels are turning, not because it's being powered through the transfer case. When you engage 4WD in the transfer case, then power will be transmitted to the front driveshaft and front wheels.

The disadvantages of the mod are of course increased wear on your front driveshaft u-joints and splined slip joint, increased driveline noise (I would think), and potentially slightly less power and decreased gas mileage (due to increased drag of turning front driveshaft.

IMO, Just troubleshoot your system and fix what's wrong instead of cutting half of it out.

 

+1 and add the manual hubs! Gas milage will go up and wear issures will go away. How do I know? I added the manual hubs (Warn) back in '91 when I bought mine new off the lot!

Chances its a vac modulator or a line is disconnected or split. Good Luck!

 

How 'bout just fixing the ADD? Your problem is most likely with the vacuum lines. Use that article about defeating it to help fix it!

 

I will probably do the ADD removal when I get my manual hubs in, but for now, I have checked all the vacuum lines and they seem good. The resistance across the VSV is good, the air flows through them as they should. I was trying to find the position sensor on the trans, maybe that is toast so it's not telling the vsv to let vacuum go to the actuator on the diff. What am I looking for down there? Also, I'm thinking it could be the relay, Where under the dash do I find the ADD relay?

 

bump. Someone must know where the relay is?

 

Have taken the vac unit off the front diff? Mine didn't work either, had vacuum down to the diff unit, finally took it off, moved the rod back and forth manually, installed, worked great. It was just stuck. Just be sure you have a pan under the diff to catch the lube, and lube on hand to replace.

 

I think I have found what is suppost to be the relay, down on the steering colum, by the firewall. All the prongs match up to the diagram, but the relay says fuel pump relay :S If this is the ADD relay, it is shot, because i dont get continuity across terminals 2 & 6 or 1&4 when 12v is applied