Recently my 4Runner has been having problems engaging 4WD when it hasn't been engaged for a week or more. When it starts acting up, I'll be able to shift into 4WD and hear the relay click as well as use low range but the 4WD will never fully engage. When it does engage finally tens of miles later, there will be no problem engaging and disengaging it. It seems like the ADD actuator seizes in place and once it breaks loose, it functions normally.

Anyone have any ideas what can be causing this? Any possible fixes?

 

It could be a problem in the diff with the ADD actuator, but I'd investigate the VSV system first:

See if there is good vacuum at the check valve between the manifold and the VSV's on the driver's fender wall. (If the check valve is plugged, a $4 generic from NAPA will solve the problem.)

Look for any loose or split vacuum hoses. A leak in the vacuum reserve can inside the fender is also possible. The two long vacuum hoses going from the VSV's down to the front diff are the engage/disengage signal. Make sure a strong vacuum switches from one VSV to the other where those long hoses plug in as you go from 2wd to 4H and 4L. If it does, problem is in the diff. ADD actuator. If it doesn't switch, then put a DMM or test light on the VSV's to see if the electrical signal is getting there from the TC. 12+ should switch from one VSV to the other. If it doesn't, problem is in the TC position switch or wiring. If it does switch but the vacuum doesn't, your VSV's are suspect. All pretty logical.

I'm betting on a vacuum leak or actuator problem, based on your symptoms.

(VSV= Vacuum switching valve).

 

I'll give the vacuum lines a good check tomorrow or whenever it stops raining here but I really think the problem lies in the actuator because once it finally engages, I can shift it in and out of 4WD with no problem. Wouldn't a vacuum leak cause it to not actuate at all?

I hope to god its not the actuator, I've pulled the front diff before and it was the biggest PITA ever.

 

http://www.toyota-4runner.org/3rd-ge...reference.html

Yeah it's on the other forum but plently of good info on the won't go into 4wd problem...a $37 microswitch in most cases.

 

1. Worth checking first because the fixes are much cheaper in this area.
2. I'm figuring a partial vacuum leak would not engage right off but as vibration plus working friction got things moving, plus a high vacuum moment like a downhill deceleration, could pop it in.

The in-and-out afterwards part is a head scratcher, I'll admit. But you would shoot yourself if you worked on the diff first and the problem turned out to be on the vacuum side, which is much easier to access and easy and quick to check out. As stated by MaxBlast, the TC position switches are also frequently troublesome, and they could also conceivably cause those symptoms. If the vacuum switches normally, you have ruled those out. The switch on the diff only turns on the dash light, it doesn't affect the actual engagement, at least on our 5spd non-electronic systems.

It is better to start in the middle at the VSV's and either fix it there, or move on to the front diff, or move to the TC switches, depending on what you find. IMHO, of course.

I haven't done it, so I'm not sure, but I think you may be able to just pull the actuator. Much easier than pulling the whole diff.

 

hey anybody know i good site to help me install a lockright locker in the front end of my 96 sr5 runner?? shop wants 1200$$$$ to put in...HELP

 

check around forums here or at pirate. i just put an aussie in the rear of mine. after searching for a while, found enough info to do it myself. good luck

 

Dude, just start a new thread, don't jack someone else's