99 Silverado with ATC automatic transfer case doesn't engage to 4WD
Thank you for your help. I got the transfer case and front
differential changed out and now I have another problem. The used
front diff with 22k that I put in is making noise when in 4WD while
under a load, or in other words, when I give it gas. It is a low
whine, almost sounds like knobby tires on the highway. It goes away
when I let off the gas and it gets louder when I am climbing a hill or
really getting on the gas. And when I turn left or right on gravel in
4WD, it makes a loud growling sound in the front. These noises were
not there before when the 4WD was working right last year. I have an
appointment to take it in Monday to the dealer to see if they can tell
me what is going on. The yard where I got the diff said they would
ship out another one if I find out this is bad. I am wondering if the
vehicle that this diff came out of was hit somehow that could have
done something to the diff. I am also wondering if I could have
installed something wrong. I went by what the GM shop manual told me
and torqued everything as recommended. The shop manual didn't mention
anything about insuring to align the axle, half shafts,etc. It did
mention to reference mark the front drive shaft when you remove it but
I replace everything (diff and transfer case) at both ends of it so I
had nothing to line it back up to. I don't know if this could cause a
problem. Any ideas?
Thanks again for your time and help,
Sound like you got a bum front axle. This happens sometimes when
you go with wrecking yard parts. It's the chance you take.
Be careful, taking it to a dealership will get expensive fast....and
they won't be real excited about looking at it if you tell them
that you have a junkyard front end in there. They will simply
look at you and ask why you don't just get another diff from
the yard you got it from.
No, I don't think that you did anything wrong. There really is
nothing to "line up" when installing these front diffs. I just think
that you happened to get a bad diff. At least...that's where I
Could it possibly be a cv joint in one of the half shalfs? How could I
eliminate that possiblity? It makes a low whining going straight down
the road in 4wd when giving it gas (the whine gets louder the more I
step on the gas), and growls when turning in 4wd. I wouldn't think a
cv joint would make noise going straight down the road, but maybe when
under torque it might. I don't know. There is no cluncking or poping
noise. Would I need to take both half shafts out to see if they are a
problem? And if I do take it in, where should I go? Should I go to
I thought that you mentioned that the noise wasn't there before
the used diff was installed. If the half shafts are the original
halfshafts, I doubt that's where your problem is. Logic is important
here....if you install a new component and all of a sudden you
have a noise that can't be accounted for by any other reason,
then I'd go with the new component.
I don't know of any way that you can take out the half shafts and
run the vehicle down the road....unless you had some old outer
c/v joints that you could install through the front wheel bearings.
This would not accomplish anything anyway...as the front diff
would now be under no load and probably be quiet. This could
give you the false impression that the halfshafts were the problem.
You could either try a dealership...(I'd go there before an AAMCO
place) or just try to find a good independent shop that specializes
in 4x4 stuff. I know that we have about 3-4 of those kind of shops
in our city.
I thought there may be a possiblity that I would not have noticed a cv
joint making noise in 4wd because I never had 4wd since last year. I
don't know if a bad cv joint would only make noise in 4wd, and make
noise under torque (will giving gas) going straight down the road.
Have you heard of cv joints doing this? I don't know if they generally
act that way. I've only noticed cv joints going bad when turning a
corner and hearing a popping sound. I agree with you that it is most
logical that it is the diff I put in. I just don't want to have the
yard send out another diff, pull this one, install the other, and find
out it was something else.
Thank you very much for your time.
It's very rare on GM 4x4 trucks to have the half shafts go bad, unless
you run an excessive amount of time with the boots split open. The
boots are quite strong (hard plastic ones) and I can't remember the
last time I replaced a c/v or tripot joint in one of these.
Yeah...I understand this. Sometimes with junkyard parts...shit happens.
I didn't know that. That is good to know. Now that you mention it,
that is the only time I have replaced cv joints in other vehicles was
when the boot was split. These cv boots are fine. Maybe I should save
the hassle and just have them send out another diff. I have one more
question that came to mind. When turning a corner in 4wd, would the
noise increase from a low whine to a loud growl if the front diff was
bad? What I am wondering is, is the only thing that notices the
increased load in a turn with 4wd engaged the cv joint, or is there
more pressure on the gears and bearings in the front diff when turning
a corner also?
That's what "driveline windup" is all about. When you turn
a corner the front and rear driveshafts will be going different
speeds and if you have the t/case in 4hi....there is nothing
to compensate for the different speeds. If you have the t/case
in AUTO4hi...then in theory the clutch pack would allow enough
slippage to allow only a minimal amount of "windup".
Which is why folks shouldn't be running around in dry conditions
in Auto4hi.....because you are forcing the clutch to slip any time
you turn corners.
And, getting back to the first point, driveline windup will put
all sorts of added pressure on the front diff bearings and gear
set...so that if there are any marginal bearings...this is when you
will hear them.
Well, I went and swapped out the front axle with the original one I
had and it does the exact same thing. I got out and listen to it while
my wife drove it around in a parking lot and it sounds like the
growling sound made be originating further back, like under the cab
area. Couldn't really tell. When you are sitting inside the cab, it
sounds like it is coming from up front. I think I will give up and
take it in. At least I have 4wd now. Have you ever heard of a transfer
case or transmission growling when making corners in 4wd or when
giving it gas in 4wd?
Yes...it's quite possible that the t/case that you replaced is also
the culprit. Listen, go get a professional to diagnose the problem
properly. Otherwise it's all just a bunch of guesswork. Who knows,
maybe that professional will declare that it's a normal condition.
Well, The dealer said that the noise is normal for this model truck so
I guess I am all set to go now. My 4WD is working again and ready for
that next snowfall. They said on dry road conditions it will make
noise due to the transfer case clutch doing its thing, I guess. Thanks
Ian for the help.
firstname.lastname@example.org (SDNomad) wrote in <80bcbb59.0311151451.5616a021
I have a fair amount of experience with independent rears on european cars
- because Ive had two failures... One was a CV boot failure that seized up
the side on the interstate, the other was internal to the diff.
The sounds you are referring to sound to me like the input bearings are
bad. Perhaps there was water cotamination inside there, which pitted and
messed up the bearings.
Try using redline synthetic diff oil. You might even try the 85w-140 stuff.
There is often a dependence on noise level with oil viscosity, so you want
it to stay thicker through the temp range.
If thats not working, Id say bring it to a rebuilder who specializes in
diffs. Im sure he can get the parts and make it like new for cheaper than
one from the dealer. If you take out the diff and re0install it, Id bet
itll be real cheap, maybe $350-400 (the cost to rebuild my BMW 4.10 LSD
with BMW parts). Of course to take it out and put it back in will add on a
few hundred extra.
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