well my runner has me stumped on this one. I have a 96 2.7 and after replacing a steering rack and power steering pump and sitting for the winter months ive discovered that my 4wd wont engage in the front diff. when i shift it down into 4wd it shifts into the transfer case but nothing in the front diff (light on dash does not come on). I have went over the vacuum lines and cant see any cracks or leaks.
So my question is where should i be checking for a problem.


Thanks, Tim

 

first when u put it in 4wd do u hear a click in the dash area? have u checked at the actuator to see if u have vacuum on the 4wd side? side closest to the electrical plug? do u know for sure that the actuator is moving? they do get gummed up a little sometimes and u need to pull apart and clean and reinstall. if that's not it then check the switch down on the diff that it has continuity threw it when in 4wd, if not that then i would look back at the indicator switch on the transfer case.

 

Yes I do have a click in the dash. I have a closer look at the actuator see what kind of problems i can find there

 

This is all good advice. I would add that the twin VSV's on the driver fender wall are also a possible trouble area. There are two long vacuum hoses that come up from the diff, one goes to each VSV. Check to see that one of the two hoses has vacuum (engine running, 4WD NOT engaged. If no vacuum either side, check the check valve going to the intake manifold and look for loose hoses or a hole in the reservoir. If there is vacuum on one hose, then put it in 4WD. See if the vacuum switches to the other hose. If it does, and no 4WD, problem is the diff actuator. If it does not, then just switch the hoses and you should go into 4WD. This confirms diff is okay.

OK, switch them back. Then use a test light to see if electrical signal from the TC also switches sides of the VSV. If it does not, problem is the switch on the TC as justin said. If it does, but the vacuum does not, the problem is the VSV itself.

I start troubleshooting at the VSV's because you can figure out where the trouble is without having to climb under the truck.

 

thanks guys, this is helping me understand this vacuum system a lot more. it seem i got a lot of good vacuum going too the actuator when in 4wd. While i was out frigging around checking over all the vacuum lines again i unhooked a line coming from a vacuum valve (parts number 25860-75160) up along the fender in the drivers side. when i hooked it back on it kicked into 4wd. so im not sure if that vacuum valve would be a problem or not?. i think put it back into 2wd and could not get it too engage back into 4wd again.

 

here is a diagram and pics of some more info on the system.

http://www.ncttora.com/fsm/1993/susp...26addcontr.pdf

see if any of this might help if not look for the one for the yr of your truck.

 

hey there yota fans i have 85 excab automatic have a problem with it not going in to 4 high or 4 low could this be a transfor case prob would be great to get some advise thanks yota willy

 

Please don't post things that have nothing to do with the model in question. Thanks.

 

This post doesn't tell me what I need to know to help you or answer your question. There are two lines sending vacuum to the actuator. (The 2002 is electric, that's why that on-line FSM is useless for us earlier years with vacuum.) One line pushes the actuator so that the diff axle sleeve is in locked in the 4WD position. The other line pushes it the other way so the sleeve retracts and the wheels are free from each other. Those valves on the fender wall decide which hose gets the vacuum in response to electric switches on the TC. Only one line gets vacuum at a time.

Follow my procedure and you will know if the problem is in the the diff, the VSV's, or back at the TC. You need to be specific about which VSV you connected the hose to, and where the TC was set when you did it, and then what happened when you changed the TC back again. Does the vacuum switch between valves when you choose 2 or 4WD? is the big question you need to answer. The second one is: Does the diff engage and disengage when the vacuum switches hoses?

 

I know this is an old thread but I have a 96 4runner 3.4l that is not indicating 4wd. I was trying to follow your instructions and have no vacuum from the 2 long hoses coming from the differential. I looked at the check valve side coming from the intake manifold and I have good suction. Can't find and holes or cracks in the vsv reservoir. Any ideas?

 

Well, the long hoses are never going to have vacuum. They get vacuum from the VSV on the fender wall where they connect. So, the key question, do you have vacuum on one of those nipples where the long hoses connect? Does it switch sides when you go from 2wd to 4wd?

If you are saying those nipples never have vacuum (no vacuum TO the long hoses, as opposed to FROM), then check the other hose to each VSV. Do those have full-time vacuum? If they do, does ONE of the wires have a 12V signal? If neither does problem is the VSV.

I can do this all night. You need to test things and report precisely what you find, or we won't get anywhere. I need something to work with.