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  1. #1
    Sr. Apprentice alwcurlz's Avatar
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    Default 99 Z71 Front end growling howling whining differential or wheel bearings??

    I have a 1999 Silverado Z71 with 134,000 miles on it. Purchased it last month.
    The front end growls at lower speeds then increases in pitch as speed increases which is quite annoying. Also a slight vibration can be felt while the front end is humming at lower speeds.
    In trying to determine the problem I assumed it was the bearing on the driver side. I purchased some bearings and went to remove the wheel in preparation. While the wheel was off, I thought I'd take and turn the rotor/hub and could hear/feel something like what would produce the sound. However, it wasn't really coming from the bearing when I put my ear near it. I listened near the differential and turned the rotor while putting my hand near where the short axle enters the differential. I could feel a slight vibration and hear the sound and realized that the differential may be the problem. I checked the other side, long axle side on the passenger side and it is smooth/quiet. I did notice that there was a mess of oily dirt on the skid plate under the differential and on the differential itself. Leaking unit. I removed the filler plug and then proceeded to add 18oz of gear oil. Ugggh. So it was low and the bearing or internal components are bad? Well, I found someone on ebay selling a 99 Silverado/Sierra front differential that would work and the guy told me it had less than 10,000 miles on it. When it showed up, I thought I'd spin the axles and have a smooth spin. Nope. Just the same sound/feel as the one in my truck!! The long axle shaft side is quiet/smooth like on my truck too! Now I'm wondering if this is normal? There are rubber bushings on the mounts of the differential that would insulate vibration so the little vibration/sound wouldn't be what I hear/feel if it's normal, right? Or is it the bearing? Maybe the bearing has to be under load/on the road for it to make noise? Maybe the guy who sold me the differential said it had less than 10,000 miles of USE...and not less than 10,000 on the truck it came off of?

    Someone here must know something!
    1999 Chevrolet Silverado Z71 Off-Road
    2008 Silverado Z71 LTZ Wheels


  2. #2
    Sr. Apprentice alwcurlz's Avatar
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    Default

    Well, I got a response from the guy who I bought the differential from...said he's been doing this kind of work for 20 years. Anyway..here's what he said: "The short side axle splines directly into the spider gears. the noise you here and feel is the gears moving. This is normal."So it IS NORMAL? So I guess I need to just replace the bearing on that one side and find out for sure. Also, off-topic already...when I got the differential, I noticed the red stuff along the seams as seen in the auction was not silicone like I thought it would be because I asked him and he said he opened it up and checked to make sure it was all good inside. Anyway, when it got here, the red stuff was mushy and sticky like grease! I thought..what the?? Sealed with grease???? Packed differential with grease??? Long story short...he explained it was Anaerobic sealant. It's what's described in this forum here. Some weird stuff!! Sets up when there's no oxygen present?? Ok, that's something new for me! Must be something NASA invented. Imagine squirting that stuff into orbit! Hahah!

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