Yukon 4WD Engaged

[revvin]

I have a Yukon SLT 4Wd and when the car is engaged in 4wd I hear a humming sound from the front difrential when the 4wd is engaged. In addition, can you engage 4wd all the time on a dry surface?

[BansheeRider]

I have a 02 Denali that has full time 4wd and the there is always a slight whine.

[rzkz8k]

You didn't say what year your vehicle is so I'll assume it is between 1999 and 2003. If you have the NP8 transfer case, here is what the owner's manual says:

Notice: Driving on pavement in four-wheel drive for
an extended period of time may cause premature
wear on your vehicle’s powertrain. Do not drive
in four-wheel drive on pavement for extended
periods of time.

2004 Yukon's have Autotrac (NR4 dual speed transfer cases) and Denali's have AWD (NR3 single speed transfer cases), these systems are hydraulically coupled and fully automatic.

The wine noise is normal when in 4wd or auto 4wd.

[Eggert]

Thanks, rzkz8 for the info.
BansheeRider, FYI just in case, NP8 is an option code and they are on a sticker in the glove compartment.

I have a 2001 Yukon XL 4wd K2500 and it has an NP8.
4WD is a PART TIME setup as the road has to be slippery to allow for the front and rear axles having the same speed during turns.
AWD is a FULL TIME setup as the transfer case allows the front and rear axles to turn at different speeds.
In our case you should feel the front wheels scrubbing on dry pavement in a tight turn.
It does not feel good in the steering.

[Eggert]

revvin, just a note - you only want to engage 4WD when absolutely necessary. That would be mud or snow.

Drive settings in order of wear and fuel consumption:
2HI - best, does not turn the front driveshaft or wheels
Auto - worse, does not turn the front wheels - unless needed
4HI - worst, turns everything
Hope this is useful... Take care, E.