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Old 10-26-2016, 11:07 AM   #1
stealth_weapons
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Join Date: Dec 2010
Location: Whiteman AFB, MO.
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11 GMC SIerra SLE 4WD

This is my wife's truck and I am having some issues that I am wondering if someone can help me out with.
My wife drove the truck to work (about 50 miles from home) the other day and the truck drove fine. On her way back it started surging and making a clunking noise that can be somewhat felt in the floorboard.
I drove out to where she pulled over and test drove it myself. I got the same results at speeds of 60mph and higher. There isn't any noise when turning at low speed. I did notice the 4WD selector was in auto. the weather was nice and the roads were dry. I ended up limping the truck home and playing around with the 4wd selector and I cant hear the truck engaging into 4wd but it is in fact engaging.
I checked the transfer case fluid and it was full and not burnt. the front diff however, was extremely low and the diff was covered in grease and grime. I pulled the drain plug and very little gear oil came out and the magnetic tip was covered in metal shavings. I cleaned the plug and refilled the diff.
the truck still made the noise when I took it out for another test drive. it is weird. its not the same noise as the frozen slip yoke I have read so much about. when you drive it at 60mph or faster there is a clunkish sound that doesn't have a pattern to it. it will make the noise for a bit ten stop then it may or may not start doing it again.
I cant figure out what is going on with this thing. any help would be appreciated. and the truck has 111K miles on it 5.3L flex fuel with the 6l whatever trans that has the manual shift option.
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Old 10-28-2016, 06:49 AM   #2
68c10airstream
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Re: 11 GMC SIerra SLE 4WD

I believe the low level and metal shavings are a dead ringer for the complaints/concerns you have. I was a ase mechanic when i switched careers in 1999 so i haven't been into the newer front differentials but a clean junkyard front diff will probably be the cheapest route to go, provided you match the gear ratio!!

The biggest problem i see across all brands of awd/4x4 is the fact or continually running a low tire pressure long enough to create a smaller diameter tire. I have personally seen this destroy positraction clutches in rear diffs, make the fluid black in the transfer case of late model AUTO 4x4 systems (not your case because your fluid is clean).

In your case i believe a fluid leak in the front diff has ruined pinion/carrier bearings and these components carry enough weight and speed for very bad vibrations.

The junkyard in my area offers to swap the front diff, including a 90 day warranty, and will repair/replace in warranty any item that gives trouble. Just a thought, as garages are $75-125 an hour and then throw in parts, that front diff gets expensive fast.
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Old 10-28-2016, 09:59 AM   #3
stealth_weapons
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Re: 11 GMC SIerra SLE 4WD

Thanks for the info. I test drove it again yesterday. I disconnected the front axle actuator and drove it about 30 miles with zero noise. when I got back home I reconnected the front axle actuator and disconnected the transfer case actuator motor. when I got about a mile away from home at around 60mph the clunk noise was back. I pulled over and reconnected the transfer case and disconnected the front axle actuator. as soon as I got back up to around 60mph the noise was still there. So it seems as if maybe the actuators are ok, but once the front end is warmed up from driving a bit the noise starts... I guess this would make sense if it is a bearing or seal issue.
also, I was able to get movement out of the CV axle next to the differential up, down, and side to side with some noticeable clicking.
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