Expert: Carl Brandt - 1/21/2011

Question
QUESTION: I have a 2001 Tahoe 5.3 L.  When it snowed, I put it in 4W Low and it seemed to engage low range.  But I wanted to be sure, so I throttled up on a slight hill in my driveway.  I could only tell that both rear wheels spun.  Couldn't see any roost or marks in the snow that would tell me either front wheel was spinning?  What could cause this?  Do I need to test it a different way to be sure?

ANSWER: Ron,

Try this again, but have someone outside watch the front end to make sure that it is, or is not turning.  Another definite way to test it by yourself, is to go up the same, or steeper hill in 2-Wheel drive (preferably a hill that is difficult to make) then put it into 4-wheel drive and try it again.  If 4-wheel drive is working you will, definitely, feel the difference.

Carl

---------- FOLLOW-UP ----------

QUESTION: How many wheels are supposed to spin full time on this model in 4WD Low?  I had my head out window and watched front left and left rear tires when I did the original test.  I could see the front left wheel was not spinning at all.  I saw the left rear spinning, and saw significant snow spray from right rear, when I got out and looked - plus the car was sliding at the rear end pretty hard when I was on throttle.  The only wheel I was not certain on was front right, but again, not a single bit of roost or spray marks when I looked at the snow tracks...just a perfect imprint of the tread where the wheel rested.  I would like to test this again, but it will be a long time before next snow down here, and few opportunities to get away for off roading, but I will definitely try if the opportunity comes along.

Answer
Ron,
If your right front was spinning, then your 4-wheel drive is working as designed.  If both rear tires were spinning, then you may have a posi-traction rear end.  Normally in a stock 4-wheel drive, only one tire on each axle will spin.  With a standard differential, you have spider gears that allow one side to spin faster than the other.  Without this, you would be scrubbing the tires on one side or the other every time you go around a corner.  The tire that spins will be the one with the least traction, hence it could be the right or the left depending on the circumstances.  As far as needing snow to test it, any slippery surface, such as mud, sand or just wet grass are good areas to test it in.

It sounds like the front end may not be engaging.  Some of the Chevys have a clutch system in the transfer case that drives the front end and can slip if worn or the transfer case oil is low.  Also many Chevys have a unit in the front end that engages the axles automatically when you put it into 4-wheel drive.  If this unit is bad, then the front end wont engage.

This is the reason that many vehicles have a posi-traction unit of some type installed in the differentials.  A posi will assist in the traction department by forcing both tires to spin equally thereby giving traction to both tires on that axle. There are different types of posi units and some are more dependable than others.  All posi units will slip a little.

Now if you want to go hardcore, you can have lockers installed.  They actually lock up both tires on an axle so that they are forced to spin equally when given throttle.  There are several versions of these also.  Some are called automatic, then there are switchable units that you can engage and disengage as needed.

Few people run lockers as they have some interesting handling characteristics which are not liked by most people that use their rigs as daily drivers.

I have lockers in my Jeep and my Samurai, but they are used on some extreme trails that require the needed traction.

Carl