2nd Post

maybe if you posted a little more info, as to what year the truck was and
what kind maybe someone would respond.

What year Chevy/GMC are you referring to? Is it when accelerating,
decelerating, cruising, or all the above? Have you pinpointed it in the
t-case or front end? Does the 'humm' change when turning?

    Just so we know, your not running on-road in 4WD are you? If so, you
could be getting a bit of bind causing the 'humm'.

Thanks to the two posts.

I am running a 98 GMC Sierra Z71 with an RCD 4"-6'"  lift kit and 33"
BFGoodrich All terrain's.  I am running off road and was experiencing this
humm mostly in 18" to 24" ruts full of mud and water.  The hum is constant
but less in the smooth trails and as the rpms go up, so does the humm

Thanks ,

Blair

Automatic Trans? Was the lift installed EXACTLY by the directions? NO cut
corners or 'that's close enough'? I don't deal too much with IFS lifts so
someone else might be a better source. BUT, with any lift, driveline angles
are different and too severe of an angle can definatly cause a vibration
and/or hum.

    Does the truck do it at all in 2WD? If not, I would definatly suggest
front driveline or t-case, and only a slight maybe at the trans...extra load
form driving 2 more tires and all the drive components and the t-case AND
off-roading.

    Keep us updated as you find or eliminate components.

Hi Shades,

The truck doesn't make the noise in 2WD.  The hum is fairly quiet in 4HI and
gets louder and sounds a bit like it is groaning when climbing out of large
ruts and heavy mudded terrain under 4LO.  The lift kit was professionally
installed by a very reputable 4WD centre and they back there work well.
They in fact talked me out of two more inches of lift as they said it would
start to compromise the satability and reliability of my driveline
components.

Thanks so far for your input,

Blair

"Shades" <shades_1970(at)netins(dot)net> wrote in message

    How long has the lift been on? Could you get ahold of the shop and ask
them to give you a free inspection to make sure everything is ok? The NP241
isn't exactly a strong t-case and might be getting warn enough from the
extra load. The front diff is also only a 7.5"(if I remember correctly)
which is a pretty weak pumpkin for that big of a rig PLUS bigger tires! The
front diff internals are nearly the same strength as a rear diff internals
in an S-10. Have it inspected. If it needs work, don't do OEM parts. Go with
some really high grade perf stuff...Bearings, R&P, keep running the
synthetic. In your own driveway you can check for loose u-joints(should all
be greasable for longer life and maintenance), loose u-joint straps/u-bolts,
loose wheel bearings assemblies, warn CV shafts, etc...

    There typically is a small amount of 'humm' in 4WD, but it's better to
have it checked out and be nothing than to let it slide and be stranded in
front of all your Buddies! Trail fixes aren't cool unless you get to watch
someone else fix someone else's rig.

Hi Shades,

Thanks for the input.  I will have the shop install their install work and I
will also look into upgrading the existing parts to some better stuff as
advised.

Really appreciate the good advice,

Blair


"Shades" <shades_1970(at)netins(dot)net> wrote in message

Let us know how the inspection turns out.

    Try something for me, find a nice gravel, sand, dirt area that's fairly
flat and smooth and test it in all directions, at various speeds, turning
different amounts, accelerating and decelerating, etc...maybe even put it
into 4LO and have a friend trot along side listening from both sides trying
to find the area its coming form. Its always good to have a few ideas about
what the problem is before going into a shop.

Great advice, I'll do that this weekend.  I think it might be a bearing but
I'm not sure.

Blair

"Shades" <shades_1970(at)netins(dot)net> wrote in message