No 4x4 Bad actuator and more.

[MwTvvo]

Hello all,

My four wheel drive isn’t working and the normal troubleshooting steps aren’t sufficient. I’m doing these tests with the truck in 4hi and the key in the on position. I have the two front tires off the ground. When in 4hi the front driveshaft doesn’t spin (back tires on the ground). I can use a socket and engage the front end and this engages both tires and I can see the front driveshaft moving. Also with the front diff engaged, I checked the switch for the light and it works also.

The two abnormalities are, the actuator acts like a shorted wire when I connect 12v. I’m assuming this is a bad actuator, but I’m also not getting 12V from the transfer case (light blue wire). The transfer case switch is working correctly. I pulled it out and checked it with a multimeter. However, the switch isn’t getting 12V either.

Looking at the schematic, it appears that 12V comes in on a brown wire from the convenience center. I found that brown wire, (measuring continuity) and it’s doesn’t have 12V.

I do have 12V on pin 420 on the front axle diff solenoid. This goes to the tic/stop switch. This part throws me off because this would be a second 12v source.

Anyone have any thoughts? Thanks I’m advance.

 

[RichLo]

Please let us know what your dealing with...

Push Button or Floor Shift T-case? 4-hi means very different things especially with the key off
Manual or Auto transmission?
What year truck? (means different front diff actuator design)
How many miles on the truck?
When was the last time it was working?
Has anything changed since it was last working?

I assume you mean you put a socket inside the diff actuator to manually lock the actuator, is this correct?

 

[MwTvvo]

It’s an automatic 88 k1500 with a shifter. The truck has 220k and the four wheel drive worked about 2 years ago (haven’t used it since). The transmission was rebuilt almost 2 years ago (4x4 worked after the rebuild), but the transfer case has unknown mileage. It could have as many miles as the truck.

Electrically, I’ve added power windows and door locks to the truck which were a direct swap from a donor truck at the salvage yard. (Maybe that’s why it’s not getting 12V? I dunno).

Correct, I used a socket and the original thermal switch to engage the differential. Good questions. Thanks for the reply.

 

[RichLo]

Floor shifted T-case and a socket in the front diff means there is nothing electrical keeping 4wd from working...

unless something is wrong with the mechanical parts.

Is the socket long enough? Did the pushrod for the actuator go into the large side of the socket?

In my Plow truck I have it locked into full time 4wd manually just like your trying but I learned that even if you stick a socket in the actuator it can still disengage. I had to add washers to the large side of the socket to make sure it was fully seated.

With 1 front wheel up you should just be able to barely thread in the actuator before you start feeling resistance then hold the driveshaft (In park or manual trans in 1st) and rock the wheel as your threading in the actuator with a wrench. If you feel a binding on the actuator stop and re-assess. You need to make sure that your engaging the diff teeth as your screwing in the actuator.

If the actuator is fully in and you can still spin the 1 elevated wheel with the t-case in 4wd and trans in park or 1st then you did something wrong, you probably need more spacers/washers in the socket.

 

[MwTvvo]

I should clarify a little more. I used the socket to test the solenoid switch and the front differential engagement. The diff does engage with the socket and the solenoid switch is working too. Also, the transfer case is engaging because the front driveshaft doesn’t move when in 4hi (but freely in 2hi & neutral)

I believe this is an electronic issue (besides a possible faulty actuator), and I want to keep everything factory or maybe upgrade to an electronic actuator. I can replace the actuator, but I’m not getting 12V to the blue wire, so a new one won’t work either. Also, when I apply 12v to the actuator, the wires start to smoke like it’s shorted out (am I testing this correctly and the actuator is bad?)

Here is the schematic I’m using to troubleshoot. I’m hoping to clarify some of the theory on how the factory setup works to determine where my problem might be. Of course, I could just run a separate 12v source to the transfer case switch, but I want to try to fix it before bypassing

 

[yevgenievich]

Older thermal actuator when going bad often will short. Would blow a fuse as well. Good actuator will also have very low resistance, but should keep the current draw peak under 10 amps or so

 

[MwTvvo]

Well, I don’t have any blown fuses. According to the schematic, the 4 wheel drive taps off the a/c fuse. That fuse isn’t blown and does have 12v, but there is no continuity between them. Is there supposed to be?

That’s good and bad news on the actuator. I’ll have to pick up a new one. Thanks for the reply.

 

[MwTvvo]

Thanks for all the replies. I’m still missing 12v at the switch of the transfer case. I do have 12v on the pin 420 of the front axle solenoid switch and all switch are working, verified with a multimeter. Does anyone know how this circuit works and where the 12v comes from?

 

[Schurkey]

The thermal actuator works with power (light blue, circuit 300) and ground (black, circuit 150), no additional wires.

Black 150 wire goes through a 3-wire connector, and a multi-wire splice, but actually plugs into and grounds at the "Convenience Center". This is--apparently--still functional on your truck.

The light blue 300 wire gets power via the Transfer Case Switch, which itself is supplied by power from a brown circuit 50 wire. Brown 50 from the Transfer Case Switch goes through a splice, that same 3-wire connector, another splice, and ends up plugged-into the Convenience Center. At the other end, it goes past the Transfer Case Switch to the Front Axle Solenoid Switch. APPARENTLY Circuit 50 gets power from the 25-amp AC-Heater fuse.

Power on Purple Circuit 420 of the Front Axle Solenoid Switch means that you have power on Brown 50 beyond the Transfer Case Switch, so the break has to be between the connector for Brown 50 at the Transfer Case Switch, and the Brown 50 splice that continues down to the Front Axle Solenoid Switch.

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