4x4 question

I have a 99 blazer. The auto four wheel drive works fine but when I select four high or four low the front wheels don't engage, I can hear the transfercase shifting however.

I have a 99 blazer. The auto four wheel drive works fine but when I select four high or four low the front wheels don't engage, I can hear the transfercase shifting however.

How many miles on it ?
Has the transfer case ever been serviced with the GM blue auto track fluid?
And 4W lights or check engine blinking or flashing?
How are you checking for front axel lock in?
Any code?

Thanks for the response. It has 157000 miles, their are no service lights on either. I just bought the blazer a few months ago so im not sure of the service history. The way I was checking if the diff was locking was on sheer ice, the front wheels would not spin in 4 hi or 4low but they would instantly in auto 4wd. the indicator lights on the buttons were not blinking either, they were solid within a few seconds of selecting them.

The auto matic 4W can be tested with a Transfer case capable scanner.
If not working right there should be a code or check trans/transfer case light.

Jack it up and see if front drive shaft is locking in in 4W High or 4W low.
Post back what you find.

Ok, so I tried a few more things. First I jacked up all four wheels, put it in drive and tried all functions. All four wheels turned and the front diff was deffinatly locked in and everything seemed to be working fine. Then I put logs under the rear axel so that the wheels were just off the ground and let the front end down completely and tried again. As soon as the wieght of the front end was on the ground the front wheels would no longer turn in 4 hi or 4 low but they would in auto 4 wheel. Still no service lights on the dashboard.

That is strange or sounds like it is working backwards.
Have you checked the fluid and fluid level?
Has the transfer case ever been serviced?
They should be serviced with the GM auto trac blue transfer case fluid.

If you do not need 4 wheel low and it pulls good in 4W auto mode I would just drive it like that.
But I would still service it with the good GM fluid which may help on the problem.
There is a viscious clutch inside the transfer case that may not be holding or working good due to no service or low fluid or someone has put the wrong fluid in it.

After proper service if it still does not work as should and you still want to fix it get it on a transfer case capable scanner and look for the problem.
If it is not working right a good scanner will do some test to check it out and show the problem and have a code stored.
Good Luck
MT

Thanks for the tips and info.

You are welcome and hope it works out or you.

Remember
4W high or 4W low are for off road use only.
Do not run them on a dry surface in 4WL or 4WH.
4W auto is more for slick or wet highway running and is made to work have 4W traction when wheels slip.
If you payment is dry always go to 2W drive.
Good Luck
MT