How do modern 4WDs work?

[kodiakisland]

OK, I know this sounds stupid, but how do modern 4wds go in and out of 4wd? I have a 2003 avalache that will not go into 4wd. I assume its the actuator because thats what I've been told. Not that I know what the actuator is.

I've had two first generation blazers and a 91 that I've done all the work on myself. I fully understand the transfer case/solid front axle set up and have disassemble/reassembled with no problem. I have never worked on anything modern and don't even know what happens when I push that 4wd button.

What happens when I push the 4wd button? Does that engage the transfer case or does it engage the front axles? I assume my transfer case only supplies power to the front shaft when its in 4wd, but who knows? How about this actuator I've been told about? Is that what shifts the transfer case? Is it all electronic, vacuum, or what?

When I get it working, I'm planning on trading it for something a bit older with less wires. I don't know if that makes me stupid or just old.

 

[lectric80]

I don't know if it is the same on those as the older ones, but the older ones had an actuator under the hood that engaged the front differential. They were at the time vacuum operated and problematic. The newer ones are a bit more complicated, but I believe they still have this actuator. There is also a motor on the transfer case that engages the case when you press the button. Normally any issue with that motor will turn on a Service 4x4 light on the dash, but I don't know if it will do the same if there is an issue with the front actuator. If it is that actuator it should be possible to located on the front differential, if it has one. Like I said I haven't dealt with anything that new.

 

[owenst7]

Passenger side of the center section has an axle tube with a 2 piece shaft in it, actuator is near the center on the front of that tube, usually pretty easy to get to and you should be able to remove/inspect it relatively simply. It's about the size of an apple juice can but a bit longer. They are electric, so they've got wires coming out of one side.

There's also an electric motor that shifts the tcase, you can usually hear that one if you're paying close enough attention, so it's easy to diagnose without much effort.

So basically, passenger side axleshaft disconnects to eliminate force input from the wheel, and transfer case disconnects front driveline internally. Kind of like driving with your passenger side hub unlocked and the tcase in 2wd.

 

[KansasTwister]

Sounds like what my brothers jeep does then, open front and disconnects the passenger side axle.

My buddys 07 Has an automatic 4x4 xfer case in it, So it will decide if it needs 4x4, does it use wheel speed sensors to decide or what? Seems extremely problematic to me.

 

[Fordum]

Does it have lo range? If so, try to shift into that. That will tell you if its the transfer case motor or the front axle.
If it goes into low range, then its probably the front shifter.
Don't know which version you have, but the worst ones were the electric heater ones.

They are a sealed unit filled with some kind of liquid. When you want to shift into 4wd, it turns on a small electric heater inside the unit.
This boils the liquid and the pressure pushes a piston which makes a plunger come out and engage the axle.
In cold weather this takes a longer time, plus it disengages when you turn off the truck.
Usually the heater element burns out, or the liquid leaks out. Sometimes the wires get disconnected.

If you have that type, Warn makes a manual replacement. You remove the actuator and put a housing in its place. Then you run a cable into the dash with a handle.
When you want to engage the front axle, you just pull the handle and a plunger does the work.

Easy to do, I have helped install a couple. But they are mostly for more hard core offroaders.
Folks who just use it on the highway usually just fix the existing system rather than making it look different inside.

However, since yours is pushbutton, there may a little more involved. If you try to engage 4wd sometime when you shouldn't with a lever, you will hear the gears grinding and stop.

But an electric motor does not care. If you push that button, that motor is going to keep trying to force that shift until something gives.

So most pushbutton systems have a controller inline that will not let it try until it is ok to do so.
For instance, on my car, low range will not try to engage until the transmission is in neutral, the car is not moving and my foot is on the brake.

Don't know if yours is set up that way, but it would be just one more thing to go wrong....

Try to isolate it between the transfer case and the axle by either trying low range or listening for it to shift, and then we can tell which way to go.

 

[GMC1977]

on a avalanche like you have it has a motor on the transfer case that engages 4x4

 

[kodiakisland]

It sounds like my problem may be the motor to the transfer case.
When I push the AWD or 4WD button, it blinks for about 10 seconds and then goes back to lighting up the 2WD button. I'll have to see if I can hear the motor trying to work or not.
Thanks

 

[lectric80]

That is most likely the actuator. The light flashes until the front axle engages, and if it doesn't engage then it will return to 2 wheel drive. No point in putting power to the front since it could do damage with only one axle engaged.