Installed Transfer Case Now Getting Service 4wd Light

[Westlotorn]

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 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.

[gmtech4]

holy shit ...dude..

 

you paid for a diagnoses a million times over ,

 

have the truck scanned ....the message means nothing ,

 

report the code

 

as for the vibration......sell the truck...fixed

[gmtech4]

holy shit ...dude..

 

you paid for a diagnoses a million times over ,

 

have the truck scanned ....the message means nothing ,

 

report the code

 

as for the vibration......sell the truck...fixed

 

sry for the double post,internet took a shit

[Westlotorn]

Over a couple years I have chased the vibration several times but this is not my daily driver and I turn my own wrenches so it has not cost a lot but when I use this truck it works hard and usually on long trips so I want it right. I have not justified replacing it since it is used so little.

[gmtech4]

whats the code?

[Westlotorn]

whats the code?

 

My scan tool won't read chassis codes. I suspect Speed Sensor but have not replaced one so this is new.

[Westlotorn]

Answers and one more issue to work through.

 

OK, I fixed the Service 4wd issue, pulled the three speed sensors out of the old transfer case and put them in the new one in my truck just to check. The speed sensors all seem to be the exact same part number by the way. One of the sensor's removed had a little water in the connection, I think this was causing my issue. Now the 4wd engages with no Service 4wd light coming on at 35 mph. High and Low 4wd work well.

Strange thing is the Auto 4wd does not seem to work well. The vehicle shudders when turning with the auto 4wd engaged, my old transfer case never did this, it was always smooth.

2wd works perfectly. Since my old transfer case worked very well I may take it apart when time allows and rebuild it with the transfer case saver that covers the pump housing add new bearings and seals and re install.

 

Now for the elusive vibration at 62 mph. I installed another driveline just to test it today. The original driveline in my vehicle had been rebuilt and then balanced 3 times and the vibration was always the same.

 

The driveline I installed today eliminated the vibration completely. I could have saved a lot of time and money if the original driveline had been repaired correctly. I am really sorry to say I paid to have it rebuilt the first time, when the vibration was still there that company re balanced it for me. When it was still there I went 100 miles away to another balancer to make sure the driveline was balanced. This shop told me the balance was off slightly and they had corrected it but they also said it was so close I never should have felt it. After all that I put a used driveline with 86000 miles on it into my truck and the vibration is gone.

 

Makes me wonder if my old driveline had a bend in the shaft or some oddity that did not show up on the balancing machine. I believe both shops actually tried to give me good service but this sure has been a pain in my A**. Thanks for listening, I had to rant.