Is it possible to 'spring' a transfer case? I was heading out of town
on ran into black ice as the freeway started up hill. There was quite
a bit of traffic and I started to fishtail on the Interstate at about
35 MPH. I didn't check the speedometer but guess I was around 30 MPG
when I pressed the 4H on my 1997 GMC Suburban to engage the four wheel
drive and heard a fairly loud CLANK.
So far everything is, and has been working fine, but for some reason
at around 50 MPH, I hear a kind of loud whining that either sounds
like tire noise OR my transfer case. I wonder about this 'sprung'
transfer case thing because years ago, a friend had an old Ford 4x4
pickup that howled pretty badly at highway speeds and he told me that
he had 'sprung' his transfer case (never said how he did it, though
his would have been of the year where you had to be at a complete
I was under the impression that with the push button to engage 4x4 GM
products, a person could be rolling down the road at 30 MPH (or so)
and be okay doing this. I guess in retrospect, I'm still glad I did
it because I think it kept me out of a winter nights freeway collision
but am a little concerned about the howling sound (again, kind of a
loud road noise sound).
Anyone else experienced this or have ideas?
Here is a quick outline of how the GM system (and most other pushbutton
systems) NORMALLY operate.
You are driving at whatever speed.
Reach out and hit the 4Hi button.
The button tells the controller which does a few things.
First it sends a signal to the transfer case telling it to engage. This
allows the parts in the front drive line to get up to speed (normally on
a GM the only parts turning in the front are the pinion gears).
It then sends a signal to the front axle to engage. Because the
internals are already turning at the same speed it locks in nice and quiet.
The switch on the front axle then tells the controller, "I'm all set"
and that turns on the 4X4 light AND changes the ABS programming at the
In your case you were on ICE, and fishtailing, That means that the rear
tires have lost traction and could be actually turning 40-50 mph. The
FRONT tires which still have traction may have been turning at 30 mph.
That speed difference is what caused your bang. The front axle tried to
come up to the speed that the transfer case was at AND tried to slow
down the rear axle and transfer case at the same time.
That is NOT a good thing.
While shift on the fly works great you DON'T want to try shifting while
the rear tires are spinning and the fronts are going slower.
The growl could be a damaged chain or bearing in the T-Case or a problem
in the front axle.
I had a T-10 in yesterday that the owner did this same thing on. On that
one they were VERY lucky, it just snapped the front drive shafts rear
There is going to be some noise in 4wd at speed but I cannot say if
yours is excessive without hearing it. The "clunk" was because
synchronize in Tcase is likely getting worn and not smoothly bringing
front drive shaft up to speed to engage it. Realistically, shifts in to
4wd should be made a a lower speed because it is easier to get drive
shaft up to proper speed to engage it. (20MPH or less)
On 1/27/2009 10:35 PM, firstname.lastname@example.org wrote:
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