CLUBFOOT

1995 T100 DX, 3.4L V6, AT, 136,000 mi.

Having 4WD issues with my new to me T100. I searched the forums and tested a few things but I do not know where to go from here.

When 2WD is selected, the front diff can be easily turned by hand. In either 4WD selection, it cannot be turned by hand.

I have no 4X4 light on dash.

Checked vac lines. Have good vacuum from source to the 4 way. Tested both VSVs in 2WD and 4WD and get no difference - only vacuum at the brown side nipple.

I tested the plugs for the VSVs and the brown side shows battery voltage. The blue side shows no voltage.

There were mouse turds in the glovebox?

Need help from here. Thanks in advance!

Zpd426

I know the 4x4 light has a wire going from the front diff up to the motor on the driver side. Its a crappy connector and can come loose or break. If it does the 4x4 light wont turn on but 4x4 will work fine.

what do you need help with specifically?

250000_yota

It sounds to me like you have 4wd, but the indicator isn't working. The chain of events in this style 4wd go from the transfer case going into 4wd with the lever, sending a signal to the VSV's, which switch vacuum to the actuator to lock, then the actuator locks on the front diff, closing the circuit for the indicator light. If your saying that it locks, but still no 4wd indicator, then yu need to start chasing the wiring from the indicator up to the bulb.

CLUBFOOT

My main concern is that the VSVs are not switching vacuum. I also wondered if both VSVs should show voltage at their connectors. In my case I only have one showing voltage. This is what led me to believe the 4WD system is not working at all.

I also wondered where my blue VSV sources power.

I am not able to get all four wheels off the ground here at home so it is hard to say if it is working or not.

Thanks for the replies.

CLUBFOOT

Had a chance to test the ADD switch tonight and it had continuity when I pressed the button.

Anybody have any suggestions on what to check from here?

Thanks.

CLUBFOOT

Also, tonight I found a connector under the hood that wasn't connected to anything. It is split off from a connector that leads to the brake fluid reservoir and looks like the same type connectors that the VSVs use. It had no voltage when I tested it and has green/white and red/white wires coming from it. Anyone know what its function is?

CLUBFOOT

I have been messing with the truck again today. Looked for signs of mice in the wiring or bedding but came up with nothing.

Did find the specs for the VSVs and tested them - both fell within spec.

Whats the next step?

Zpd426

Ive reached the limit of my knowledge with this one

CLUBFOOT

Can anyone shed any light here?

CLUBFOOT

Anyone?

JasonYota

iTrader: (1)

Seems like a problem with the ADD. You don't have to have all 4 wheels off the ground to test this, just the front tires. ADD works off vacuum, that's what moves the actuator in the front diff.

starrjewel

I know this might sound really silly but my 93 T100 does this occasionally. After I put it in 4WD and then take from neutral to drive, it takes a bit for the actual 4WD light to come on the dash. CLUBFOOT, how far have you driven it in gear to test the 4WD?

CLUBFOOT

Thanks for this starrjewel. I have not had any time for my T100 lately and it hurts my heart.

To be honest I hadn't had it out more than a couple laps around the block in 4WD. I will try this tonight if I get the time.

BamZipPow

Um...you really should test the 4WD system in dirt as testing it on the street will bind and potentially break parts...expensive parts.

CLUBFOOT

Got a new job, moved, and now I'm back under the truck.

I hooked up the vacuum source to the vac line on the passenger side of the actuator. 4wd works, still no light. Nice to know I can get out and manually engage it but ideally the shift can be done from within the cab.

I do know these things:

-The VSVs fell within spec but they do not switch vacuum from brown to blue when engaging 4WD.

-The ADD switch is working properly

-The actuator works when vacuum is applied to the appropriate hose.

Now, I am looking at the switch on the T case as my culprit. After locating the switch, testing it proved difficult and removing it looks brutal. Can anyone shed light on testing the T Case switch?

When I get this and the exhaust done, my uncle is painting this truck for the cost of paint. Needless to say, I am getting anxious.

Thanks.

CLUBFOOT

Up....

JasonYota

iTrader: (1)

Is the switch on the transfer case connected? That's what controls the light on the dash.

CLUBFOOT

The switch is connected. Does the transfer case have to come out to get that switch out?

Thanks.

JasonYota

iTrader: (1)

The switch should unscrew where it's plugged in at.

Bullwinkle94

My 4wd light will flicker maybe for a second when I first try to engage then nothing.. My 94' is manual hubs, does it have ADD and VSV and what do those initials stand for??