4wd not engaging. transfer case vs diff actuator question

Morning all; Original owner of an '04 TRD 4x4 V-6 double cab, ~315K. Motor, trans, diff and t-case have never been out of the truck. I replaced the transfer case actuator 200k ago. Push button ADD actuator (Not J-shift), with the electronic diff lock, no grey wire mod. Yes, I forget to put the truck into 4wd occasionally. From new, it went up to Tahoe every weekend when we were in the Bay Area for the first 6 years, then we relocated to San Diego and does 3-4 Mammoth trips and Baja surf trips every year now. Guessing 20-25k miles in 4wd?

At about 100k the truck starting having what has turned out to be the same recurring problem/symptom's that I've not seen anyone else have here so far. I had the t-case actuator changed out, it shifted into/out of 4wd smoothly but the problem came back.

What happens: I push the button, and it usually takes a few miles to turn on. I try park, neutral, forward, reverse (Not knowing if that helps) but it eventually turns on. Once it turns on, it then works flawlessly. It is now not engaging the 4wd after two day of trying at low speeds. No matter what, I always hear the actuator below me click at the transfer case when being turned on and a longer noise when I turn it off. When the 4wd won't work, the 4wd light does not come on, does not flicker, does not blink (That's the symptom I've not read others having). The front wheels do not engage. However, I can then put the truck into low range. The diff lock will not engage though, the light keeps blinking (When the 4wd system is working and in low range, it works and the light stays solid). When the truck actually shifts into and out of 4wd, it does it smoothly.

My interpretation: the transfer case is switching into 4wd, which is why the sensor will allow 4-low. But the front diff is not operating so a sensor somewhere realizes the front wheels aren't powered. (is that possible?) This is keeping it from being in 4wd and the fact that when it does work and the 4wd is turned off it disengages smoothly means the transfer case is likely working correctly.

I've seen two threads here that look promising; the transfer case actuator being gummed/rusted up and the front diff actuator's two contacts having a gap. Would the front diff actuator be the place to start? Or should I just take them both apart, clean them and rebuild? If I do that way, what grease do you use inside? Is there likely to be any other problem that I've not seen after lurking here for more than a decade? Put the truck up onto jackstands and see of the transfer case then move the front propeller?

Thanks in advance.

 

I would start with the front diff actuator. Before you pull it apart, just disconnect the harness from it, and give it a clean with electric contact cleaner. Don't dielectric grease the pins or grid of the female side, just put a little dielectric on the rubber seal. Then move on to more invasive operations like remove the actuators.

I recall one of those actuators is a pain if you take it apart too much... they have to be clocked and installed the same way, so really do your homework on that before charging in there.

 

Update: It's almost certainly the front diff actuator. I had a coworker drive it in both 2wd and 4wd while I was looking at the front propshaft: doesn't turn when in 2wd but does turn in 4wd. After reading the various front diff replacement threads, it seems that I'll have to remove the front trailer hitch>skid plates>loosen/remove the long diff bolts by the steering rack>loosen the driveshaft and raise the trans? Then get the forks into the correct position upon reinstallation & refill the diff. That sounds like all day on a Saturday and some curse words. I think the front trailer hitch is not going to be reinstalled...It blocks the skidplate bolts in front.

 

I'd start with taking the actuator apart while its still on the front diff.
I think its like 3 screws to get the plastic cover off.
90% of time, the issue is in the electric motor housing.

I don't the right voltages on the 1st gen to help you check it easier.
I might take a look at the diagrams later just to get an idea. But I bet you could check it all in the cab at the 4WD ECU.

 

I agree. Don't pull the diff. Unless the fork is stuck, there is nothing you can do in there, and even it is, it would be better to move that from the actuator attachment point.

Start with the actuator.

 

Add remove your sway bar to that list too. Even more fun when you go to reinstall the actuator in that tiny space and have to find a way to run a bead of FIPG on it and not smear it on anything so as to get a good seal. Good luck.

 

Thanks everyone. I'll take a look this weekend and see what I come up with. Adding the sway bar into the mix and the goopy FIPG may tip it into the I'll just throw money at it category.

 

Latest update: A Friday victory! The system is working! Yes! I decided to push the button randomly at a stoplight on the way home. It turned on while stopped at a light and turned off like it's supposed to. It took 4 days of trying to get it to go. Thankyou to everyone above for their advice; it's obvious that it needs a cleaning/greasing in there at some point and I'll be referring to this when I get in there.