Mysterious 4wd problem

Yea those values are fine, your always gona have a slight variance in voltage.

Needles make fine backprobes in a pinch so nothing wrong with that either.

 

So all my tests come back normal except the ADD in 4H which reads 12.2 instead of 0, and 4WD (B22) which reads 0.07 instead of 0.

Can you think of anything else I should be looking for other than an improperly installed actuator (or something in the differential that is blocking the collar from moving its full range)?

(The actuator tested fine before installing in the differential. I didn’t check voltages but plugged it into the harness and observed the fork move as expected, and watched the dash illuminate as expected.)

My 4L readings are currently all the same as 4H, but I’m assuming that’s because I can’t shift into 4L while the 4wd light is blinking.

 

Noted

 

Nothing to note, Tacomas don’t have manual or auto locking hubs.

 

So it's pretty much like we suspected, it's either an issue with the actuator/installation (unlikely since 2 have been tried with the same results and it works when not installed) or something is wrong in the front diff keeping the actuator from moving to the fully locked position thus the 4wd ECU being unable to complete the shift.

 

1st gens did have locking hubs back in the 90s then they went to first a vacuum operated ADD and finally the electronic ADD that's pretty much remained unchanged through the present.

The only manufacturer I'm aware of that still uses locking hubs is Ford on the F-Series trucks and they tend to be very problematic, over 90% of the 4wd problems I get are on Fords vacuum hub-lock system.

 

Yeah sorry, when I say “Tacomas,” I’m always talking about 2G+. I’m aware of the 1st gen but I don’t talk about them much. Either way, hubs aren’t relevant to this discussion since it’s a 2G, which is what I was getting at.

 

I’m assuming if I permanently fix the collar in the locked position (and spoof the actuator position for the 4wd module) I give up the ability to shift on the fly to 4H, since it could grind the gears for the TC’s front output?

 

It would still shift fine, front and rear are spinning the same speed. I deleted the ADD in my 3rd gen for a while and the tcase shifting was better and faster than it had ever been.

 

I don't think you would hurt anything if you could spoof the ADD but I'd be curious what's going on in the front diff. Your not the first with this issue but I've yet to see what the root cause/solution is.

 

Did you permanently afix the slide collar or use FJ parts? What did you do for the dash lights and 4wd module? I was just going to plug in an ADD tucked up next to the radiator somewhere.

 

I used FJ parts and I built a spoofer harness using one relay that tricked my 3rd gen 4WD ECU into being happy. It was quite easy, even on a 3rd gen with the more complicated ECU.

 

If I go the route of bypassing the ADD, making it permanently locked, is there anything else I need to worry about on the transfer case side? Seals, bearings etc.?

 

Unless the seals are badly stuck in place, it should be fine. The system is perfectly fine with spinning all the time.

 

So the only downside is fuel economy. Was the drop in fuel economy noticeable for you?

 

Didn’t notice it at all, but I wasn’t really keeping track.

 

Other thing I’ve considered, but don’t currently have the know-how, is making the ADD cable operated, and perhaps also the transfer case. There’s a member on here who has done it, using a boat throttle lever (I believe), to operate the transfer case. I think I’d want to make it twin-stick style, with one lever operating the ADD and one the TC.

 

Yes
Lol

 

I think either of those are far more trouble than they are worth trying to come up with.

 

Problem solved. I errantly installed the actuator fork to the passenger side of the engagement collar.


If you are right handed and doing this on the ground without a lift, you are probably lying on your back and left side, with your head toward the passenger tire. From here, inserting the actuator fork is very likely to push the collar to the 4wd position, and is pretty hard to see this has happened, even in full daylight. To help, I wore a headlamp upside down under my nose to shine into the ADD tube.


Looks funny but it works. However, two out of my three tries mock-installing the actuator slid the collar to 4wd, so I decided to plug the actuator in and move the fork to 4wd and slide the collar to 4wd for the install.

To help eliminate chance of error, installing the differential actuator in the 4wd position is the way to go if you are lying on your back under the truck.

I was able to get a small torque wrench on all four of the actuator’s mounting bolts — I reached the top passenger-side bolt by inserting the butt of the wrench upward past the actuator, outboard of the differential support arm. 15 ft lbs. (180 inch lbs.) is correct. (Photo to come.)

I also covered the lower end of the breather tube with a heat shrink sleeve and a liberal coat of RTV gasket maker to help prevent future water ingress. (Photo to come.)

Of note: my old actuator tested fine outside the differential, though it took twice as long to move the fork as the new one. Inside the differential, it was apparently unable to completely move the disconnect collar. I didn’t check its voltage but I would bet, based on its speed, it is only reading 6v or so. The terminals on the motor look tight and show no corrosion or evidence of arcing but a small amount of rust is visible on the motor body.