Transfer Case Installed Now I Have Service 4wd Lights

Westlotorn · February 25, 2011

Sorry, this is a Double Post, I tried to delete this copy with no success.

I have a 2002 Chevy Tahoe 4.10 gears with 110,000 miles. It has developed a small vibration that has been with me for 20,000 miles. I was convinced this was the driveshaft or Ujoints so I had the rear driveline rebuilt and balanced at a very reputable shop. No change in vibration. I had the front rebuilt, no change. I removed the front drive shaft and drove it, no change. I pulled all 4 tires off and ran it on Jack Stands, no change.

I installed a completely different real axle with 3.42 gears and drove it, the speed changed, the vibration showed up at 72mph rather than 62mph telling me the problem is in Drive line speed. If I run it in 3rd gear rather than 4th gear the RPM changes but the vibration still shows up at 62mph with the 4.10 gears. I had the drive line rebuilt and balanced again at another shop just to rule this out, no change.

When it ran on Jacks with the speed set at 62 mph and no tires on this car I crawled under it front to back searching. The vibration seemed most pronounced at the tail shaft of the transfer case.

I replaced the rear Tranny mount, no change.

I looked for almost a year to find a low mileage transfer case at a good price. I installed it this week. Vibration is still there at the exact same 62mph.

That is why I replaced the transfer case leading to this question.

After replacing the Transfer Case and filling with the GM Blue AT2 fluid the Tahoe runs and drives great, no issues except for the previous Vibration I have been chasing now for 20,000 miles.

When I engage 4wd it seems to go in fine, it is in 4wd based on steering drag and normal 4wd crabbing if I turn and all seems fine until I hit between 30 and 35mph when the Service 4wd light comes on.

If I shut the engine off and re start the light is gone until I hit 30-35mph in 4wd and it comes on again like clockwork. I drove in low range for several miles under 30 mph and it never came on. I switched back to 4wd Hi and it works fine, shifts fine, until I hit 35mph again and the Service 4wd light comes on again.

The connections to the Transfer Case seem to be in the correct place and plugged in fully. I already feel like a fool for chasing this vibration so long but this issue just adds salt to the wound.

Any idea what I am chasing here? I assume one of the sensors on the transfer case is not working or maybe I caused a problem by moving all the wires around as I pulled and replaced the transfer case.

I tried unplugging the 4wd fuse, waited 1/2 hour, turned the key to on and off watched the lights cycle correctly 5 times and then drove it to find no change. The light came on at 35 mph.

Thanks so much for any ideas that might solve one or both of these issues.

JAMIEZ71 · February 25, 2011

Have you taken it to a dealer and had it scanned with a high power computer they use and not a little one from autozone or anywhere. There should be a code pop up in their scanner when the service 4x4 comes on.

Westlotorn · February 26, 2011

No, I have not gone to the Dealer, I was really hoping the symtems would prompt a clear problem to fix. Speed sensor maybe. I am tempted to put my old transfer case right back in. 3 hours labor and done.

Thanks