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1997 GMC Suburban Noisy Transfer Case

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 stop).

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?

thanks, John

Reply to
jcage
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OOPS, 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 same time.

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 U-joint.

Reply to
Steve W.

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 pr> Is it possible to 'spring' a transfer case? I was heading out of town
Reply to
SnoMan

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