I've got a problem with my 4WD that I'm hoping someone can shed some light
on. The truck's a 2003 Silverado 1500 Z71. When you put it in 4H the truck
makes a moaning sound as you come to a stop. It only does this in 4H and not
in 4 Auto. It made this same noise a year ago and the dealer replaced a
pilot bearing in the front differential. After they replaced the bearing the
noise stopped. Now it's a year later and the noise is back and now the
dealer is trying to tell me that it's normal 4WD noise. I managed to
convince them that it's not normal noise so they're going to take the front
differential apart again. I'm guessing that they didn't replace all of the
parts that were bad. Has anyone had this problem?
Yep, I'm having the exact same problem your having except mine is making the
noise in auto 4WD. You shouldn't be driving it on pavement in 4 Hi. Mine
started making a slight noise in 2hi at about 8000 miles so I took it in and
they heard it and replaced the front differential. They said the side
bearing went bad. That fixed it for about 8000 miles. Now it has 20,000
miles and is making the same noise again but this time when in auto 4wd it
has a scraping noise like metal rubbing metal. So I took it back and they
couldn't hear the noise it 2Hi and said the 4wd noise was normal. I went
back and rode with them when they drove it and pointed out the noise in 2hi.
Now they're pretending like they don't know what's wrong with it and told me
to drive it a few weeks to see if it gets worse. Well its not gotten any
worse or better and I haven't had time to take it back.
Keep us posted and let me know if they do anything to yours.
QUESTION FOR IAN: Should there be any play in the output shaft on the front
differential like if you were moving it up/down or front/back? I'm not
talking about in/out of differential or spinning. Mine has a noticeable
amout of play so I'm suspecting another bad side bearing.
Well at least I'm not totally crazy. :-)) I actually only use 4hi when I
plow and that's only a couple of times a year (I have a long driveway in
NH). The truck's going in the shop on Thursday so I'll let you know what
they find, if anything. My truck also has about 20,000 miles on it and I'm
hoping to get this resolved once and for all before the warranty runs out.
Thanks for the feedback.
If you are talking about the right and left stub shafts that come out of
the front diff.....yes, it's normal for them to move in the manner that
you describe. The left one will be quite noticeable, as it's a much shorter
shaft then the right side. The right one can move a bit, as it really only
has one supporting bearing at the end of the tube. There is another
bearing that supports the right shaft, but it's located in the center of
"another" stub shaft inside the diff, and it can have play....all this play
can add up and you will see movement at the shafts. Remember...the
side bearings support the differential carrier and crown gear, the axles
that come out of the diff are supported by other items.
By the way, it's often tough to diagnose these 4x4 noises, as it has
become normal with these automatic t/cases with the clutches to have
a certain amount of driveline noise when in 4hi. My rule of thumb is
to drive the vehicle, listen to the difference in noise level between 2hi
and 4hi (forget about Auto4hi, as it only engage the clutch 5% in
high traction conditions, and often makes no difference in noise, even
with the side bearings right out of the front diff)....if there is a
difference, I pull the drain plug on the front diff. It has a magnet and
if there is loads of metal filings...you can be almost certain that a side
bearing has given up the ghost. On trucks under warranty, I don't even
pull the diff apart to confirm...just get the parts, tell the customer he'll
get his truck tomorrow and start removing the diff. I know what I'll
Who knows? Not enough of them with
a few miles on yet. My recommendation is
that if you own a new style truck with the
auto t/case, you would be wise to change
the front diff fluid to synthetic, (which means
changing the vent too) and change the t/case
My transmission is due for a fluid change. Should I go with a synthetic or
what would you recommend? Is there a vent or anything else to change on the
transmission for synthetic? I was going to let the dealer do it since it's
still under warranty and requires removing more than one bolt to get to the
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