1998 SR5, 3.4L automatic selectable 4WD via lever next to Transmission shifter. Had an issue about 2 years ago with the 4WD indicator not coming on and no 4WD. Ended up being a faulty selector switch on the Transmission/transfer case but was repaired by the dealer under an after market warranty I purchased when I bought the truck. I had to leave the truck undriven this past winter for a couple of months due to working out of the area.

I could not find for the most part on the forum my particular issue. I shift into 4WD Hi/Lo, the indicator lights but I don't think the front wheels are pulling. discovered this potential issue when I had to try to tow my son's car out of a ditch. This was my first indication of a possible non-function of my front wheels as when I started backing up to pull him out, my rear wheels would start to spin but the fronts did not. Changed direction, changed from Hi to Lo and back again but still only getting spin from rear wheels (breaking traction).

Are there some ways of trying to exercise the ADD actuator to verify operation of the front drive wheels? If the Actuator fork is sticking is there a way of manually releasing the fork or will it require removal of the Actuator? What is the correlation between the 4WD green indicator, drive wheels and the operation of the actuator? If the light is 'green' is this just an indication that the transfer case is engaged to the front drive shaft and not linked to the actual operation of the front differential? If not what could be the potential issue while still giving you indication of 4WD engagement?

After reading some of the threads on 4WD issues, I did not notice any where about the 4WD incidator being illuminated and no power to the front wheels. Lots of threads about no indication or flashing indicator. I will trace out the vaccum lines but is the indicator tied to the correct operation of the ADD and actuator meaning adequate vaccum? Thanks guys

 

Anybody?

 

Anyone have a remedy for testing?

 

Ok, I don't have an auto so I stayed quiet. On the manual, the light is tied to a sensor switch in the front diff--if light is on, ADD is engaged. And ADD only gets the signal (vacuum) to engage, if position switch on t-case says 4WD is on. So light is pretty much a guarantee you have 4WD. I think the auto 4WD is similar.

So your problem is kinda weird. Maybe ADD engages enough to hit switch but not transmit power, or the T-case is doing a similar thing. I assume you could apply vacuum directly to the ADD to try to engage it by itself. Then you could confirm engagement by rotating the front driveshaft by hand, it would be locked if ADD is engaged. The two VSV's for the ADD are on the driver fenderwall; one to engage and one to disengage. One or the other has full time vacuum.

If I were you, I would verify that vacuum switches back and forth, depending on whether 4WD is engaged or not. You can put it in 4WD and then turn off engine, reservoir will maintain vacuum. Front shaft should be locked from both ends, but I assume it is hard to feel if only one, and which one, is locked. In your case, I am pretty sure that one end or the other is not engaged.

After this test, you will know which VSV has vacuum in 4WD (engage).So then you could route vacuum directly to the engage hose of the ADD while clamping the disengage hose. If shaft rotates, problem is in ADD/front diff. If not, ADD works and problem is in T-case.

The vacuum setup is:

manifold>>check valve>>4-way split>>
1.Reservoir
2 Engage VSV>>ADD actuator
3. Disengage VSV>>ADD actuator
4. (this is inlet from manifold)
Just pull the hose from the ADD to the enage VSV and plug it onto the 4-way in the spot where that VSV gets its vacuum from. I think it will reach. Then check shaft.

I've never tried this but it ought to work. Engine running, trans in Park, obviously.

 

Thanks for the input, will have to give it a try this weekend