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GMTechBernard
GMTechBernard, Shop Foreman
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Experience:  GM
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2000 GMC Yukon: 2wd..rough bearing coming from the front end

Customer Question

I have a 2000 GMC Yukon XL. Should the front drive shaft turn while in 2wd? If so, why do I have a noise (similar to a rough bearing coming from the front end? I have the auto 4wd option.
Submitted: 5 years ago.
Category: GM
Expert:  GMTechBernard replied 5 years ago.

Hello! If you were to crawl under the vehicle, the driveshaft should turn freely, as the transfer case has the front drivetrain disconnected in 2WD. However, while driving, the driveshaft may turn on its own, as the left axle is still attached to the carrier, which may drive the ring and pinion. Side carrier bearing failures are common on front axles and if the carrier is spinning going down the road, it can make some noise if the bearing is bad (may get louder in 4WD).

 

Another source of bearing noise could be the front wheel bearing. These vehicles use sealed hub assemblies and will make a roaring noise, which changes with speed when the bearing goes bad.

 

Another source of roaring could also be the tires. If the alignment isn't dead on, and the tires don't get rotated, the tires will "cup" and will also cause a roar noise. It doesn't take much cupping to start making noise.

Customer: replied 5 years ago.
Thanks,

It's not the front wheel bearing as I changed it out a year ago and have since re-checked it to be sure the problem hadn't returned. The shaft does not turn while in 2wd. The front differential disconnect motor is working fine and disconnecting the shaft from the front axle (I pulled the front shaft out to be sure). However while I had the front shaft out, the front drive output on the transfer case is still in tandem with the rear, no matter what range selection is made (2hi, 4hi, 4lo, 4auto). I changed out the transfer case motor as well thinking possible it was weak and not fully shifting the transfer case. Any other ideas?
Expert:  GMTechBernard replied 5 years ago.

Don't forget, there are two wheel bearings up front. One may be new, but that doesn't mean the other one is OK. Does the noise change pitch if you sway the vehicle back and forth (turn the wheel back and forth while driving)

 

Also, even though the front driveshaft was removed, doesn't mean the front axle isn't spinning. The front Axle Actuator only disengages the right axle. the left axle is always connected to the spider gears.

 

if you are abosultely sure its not in the front, that leaves either a rear axle bearing, or transfer case. I have been fooled before, with a rear axle bearing. I had a 4WD vehicle one time that had a bad side carrier bearing and I swore up and down it was the front axle, only to find out it was indeed in the rear axle. You have to remove the Carrier assembly from the axle to inspect those bearings.

 

Transfer cases have a planetary gear set, that although is not common, can fail and make similar noises. Check the fluid level and condition and see if it changes pitch or intensity in different gear ranges.

Customer: replied 5 years ago.
Thanks again..

Several things... the front wheel bearings are ok... I raised the vehicle and there's no noise from either side.

The one thing that still makes me think there is something not right in the transfer case is what your first comment was. My front shaft will not turn freely while in 2wd when you crawl underneath. The actuator on the front axle is working fine.

While I had the front drive shaft out, I shifted the transfer case manually whith a crecent wrench and the front output shaft is still locked in with the rear output shaft. There is no difference in any range.

The transfer case oil is up to level and looks and smells fine.

Thanks again!
Customer: replied 5 years ago.


Several things... the front wheel bearings are ok... I raised the vehicle and there's no noise from either side.

The one thing that still makes me think there is something not right in the transfer case is what your first comment was. My front shaft will not turn freely while in 2wd when you crawl underneath. The actuator on the front axle is working fine.

While I had the front drive shaft out, I shifted the transfer case manually whith a crecent wrench and the front output shaft is still locked in with the rear output shaft. There is no difference in any range.

The transfer case oil is up to level and looks and smells fine.

Thanks again!

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