Blazer T10 4x4 2 door 50 mph I hear a sound like moaning noise like it poped into Hight 4 wheels drive

I own a 1991 Chevy Blazer T10 4x4 2 door .I had to used 4 wheel low drive this spring when I tried to go to 2 wheel drive the light when on to the front wheels and when I get it up to about 50 mph I hear a sound like
moaning noise like it popped into Height 4 wheels drive . it louder above 50 Mph. it not just sound it is the speed of the truck it jumps into 4wd. I then back off on speed to about 20 MPH and it Pops! out and all seems find . can anyone tells me where to look to fix this I drive it in town and on back roads just never put it all together until now . but I like to drive over 50 mph ,
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Richard Brandstetter
snipped-for-privacy@verizon.net
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On Thu, 20 Sep 2007 15:18:04 GMT, "Richard Brandstetter"

It kinda sounds like front axle disconnect is stuck engaged and still spinning drive shaft in 2wd. Try this, with it in 2wd, jack up on front wheel and spin it. If it spins and drive shaft does not turn then axle is disconnecting in diff. If driveshaft spins with wheel than Tcase is in 2wd and axle is not disconnecting at diff. Last if drive shaft does not spin in step one, try turn it manually by hand and if it does not turn then Tcase is in 4x4 and axle is disconnecting in diff. If it passes step 1 and 3 then tcase and axle is in 2wd in 2wd mode. ----------------- TheSnoMan.com
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On Thu, 20 Sep 2007 15:18:04 GMT, "Richard Brandstetter"

Replace the vacuum switch on the transfer case and get the shifter adjusted properly. That will solve your problem. For a quick fix, just disconnect the vacuum hose from the front axle actuator and plug the hose. You won't have 4wd until it is reconnected, but you will have 2-Lo if you should ever want it.
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Thanks for the info will work it this week.

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