[midlifetruck]

I'm looking at a 2002 SR5, and I have a question regarding the 4WD.

As a noob, I am trying to figure out how to test the 4WD. I have one person telling me that the 4WD is not funtioning. All electronic indicators show the system is engaging, but as the mechanic put it "no one is home". The seller is telling me that there are no issues.

Is there a good way for me to test this on my own. I have read the below info regarding the 4WD system in these trucks, but I am looking for a way to verify the status of the system other than "you can just feel it".

Any help for a noobie would be appreciated.

Help me understand my 4wd system?

[JeepKiller]

Originally Posted by midlifetruck

I'm looking at a 2002 SR5, and I have a question regarding the 4WD.

As a noob, I am trying to figure out how to test the 4WD. I have one person telling me that the 4WD is not funtioning. All electronic indicators show the system is engaging, but as the mechanic put it "no one is home". The seller is telling me that there are no issues.

Is there a good way for me to test this on my own. I have read the below info regarding the 4WD system in these trucks, but I am looking for a way to verify the status of the system other than "you can just feel it".

Any help for a noobie would be appreciated.

Help me understand my 4wd system?

Have you tried going off-road? Try something that you should only be able to do in 4WD and if you can do it then it's most likely working and if you can't then it's not working haha. That's what I'd do at least... Or take your mechanics word for it.

[ShooterMcGavin]

When you care about the "health" of your vehicle, this is not recommended...
-Put it in 4WD.
-Make sure the center diff is locked (button to the left side of the steering column).
-On level, dry pavement, turn the steering wheel fully to one side.
-Step on the gas pedal.

-> If the truck feels like the parking brake is on, and some of the wheels start "chirping" (slipping), 4WD is engaged.

Better for the truck...
-Do the above on sand covered pavement or wet pavement.

Aside from knowing how it feels, chirping tires would be a major indicator that you have 4WD engaged.

Another method, perfectly fine for the vehicle, but this is along the lines of "feeling it"...
-Get on level dirt
-Engage 4WD and lock the center diff.
-Get the truck moving forward at 5-10 mph
-Turn the steering wheel fully to one side

-> If the truck slows quickly and then comes to a stop without touching the gas or brake pedal, you are almost certainly in 4WD.

[jgue467]

Originally Posted by midlifetruck

...but I am looking for a way to verify the status of the system other than "you can just feel it".

Well besides the feel, there are some sounds. There w/b an engagement and a disengagement 'click' sound as each occurs. Then when engaged you can hear the front diff make a slight whine - this can be heard from inside the vehicle even with windows rolled up.

But if you have access to the vehicle and a lift - that's another way to tell.

So who says its "not home" and how do they know that? Luck!

[Chuckles89]

I agree with the above posts. If you're on gravel with 4WD and the CD locked, you should be able to hear the front tires grabbing if you stick your head out of the window while bumping the throttle.

[midlifetruck]

Thanks for all of the help.

Based on what I am hearing (clicking engagement), feeling (kind of a push from the front), and seeing (got the front wheels in some mud) I believe the 4wd is working correctly.

My only guess is that the mechanic did not engage the center differential. If the diff was not engaged and the VSC is active, could this cause this kind of misdiagnosis?

[csp]

Yes it would. The center diff allows for slippage between the front and rear drivelines. This slippage is inevitable if you're going around a corner as the radius the front tires take is different than the rear tires.

[WallyWest]

Originally Posted by midlifetruck

My only guess is that the mechanic did not engage the center differential. If the diff was not engaged and the VSC is active, could this cause this kind of misdiagnosis?

Possible, if he saw that VSC was kicking in he might have assumed that meant that 4WD wasn't engaged. As far as I know if you get solid green lights on the dash indicator then the system is definitely engaged.

When you push the 4WD button you get what most people would call AWD. You have limited slip between all wheels and can drive on pavement safely. VSC is still active. This is true in either HI or LO.

When you push the button on the dash and lock the differential, in either HI or LO, VSC is turned off. You get a 50/50 split in power between the front and rear wheels, and can spin the wheels to power through mud, snow, etc...

However, even with the differential locked ATRAC is still active. Which is four wheel traction control. It prevents one wheel sitting on ice, for example, from robbing all the power as would happen with a standard limited slip differential. ATRAC is always active, and works on the both axles in 4WD, or just the rear in 2WD.

[Blitzkrieg]

There is an easy way to do this with no harm to your truck that is an offshoot of ShooterMcGavins unhealthy approach.

Take the truck to an empty parking and lock it up in 4WD.

Start out slowly turning in concentric circles. Baby steps a little at a time.

If you start to feel binding, you are most definitely in 4WD. If you make it to full lock with no binding, you have a problem.

The reason this works is that in 4WD your front wheels are turning at exactly the same speed and as you start to tighten up the circle the inside wheels will start to jump because the inside of the circle is shorter than the outside.

You will feel this immediately as it starts to happen. The truck will feel like it doesn't want to do what you are trying and if you push it to far it will start to buck.

If/When you start to feel the truck resisting what you are doing, stop. You have proven you are in 4WD. It's an unmistakeable feeling.

[csp]

Originally Posted by Blitzkrieg

The reason this works is that in 4WD your front wheels are turning at exactly the same speed and as you start to tighten up the circle the inside wheels will start to jump because the inside of the circle is shorter than the outside.

Right concept, wrong details. The front axle (and the rear) has a differential in it that allows the inside and outside tires to spin at different rates.

The reason it jumps with the diff lock button on is the front and rear driveshafts are turning at the same speed but the front and rear axles are turning in different radius circles.

The diff lock button turned off is what allows slippage between front and rear driveshafts on those vehicles that have a diff lock. On vehicles which don't have a diff lock button the tcase is always locked and both driveshafts will always be moving at the same speed.

[ShooterMcGavin]

Originally Posted by Blitzkrieg

There is an easy way to do this with no harm to your truck that is an offshoot of ShooterMcGavins unhealthy approach.

Take the truck to an empty parking and lock it up in 4WD.

Start out slowly turning in concentric circles. Baby steps a little at a time.

If you start to feel binding, you are most definitely in 4WD. If you make it to full lock with no binding, you have a problem.

The reason this works is that in 4WD your front wheels are turning at exactly the same speed and as you start to tighten up the circle the inside wheels will start to jump because the inside of the circle is shorter than the outside.

You will feel this immediately as it starts to happen. The truck will feel like it doesn't want to do what you are trying and if you push it to far it will start to buck.

If/When you start to feel the truck resisting what you are doing, stop. You have proven you are in 4WD. It's an unmistakeable feeling.

Yeah, but the OP specifically said he didn't want a solution that required "feel"

Besides the safe manner of feeling the difference between 4WD locked, and 2WD open...
-hear: tires screeching
-smell: tires burning
-see: mud/dirt spitting out of the front tires (tough to do while driving)
-taste: I don't think so ;)