Troubleshooting 99 Burb 4wd

[thebmrust]

1999 GMC Suburban K1500 5.7gas OEM everything.

When I switch the button from 2wd to 4hi it’s normal sounds until I hit about 20mph then it’s a sort of sandpaper noise. Not grinding but not smooth.

BUT when I select Auto4wd, there isn’t any additional noise at any speed. (Yes the wheels lock in).

The front wheels are locking with both options. 4wd has noise, Auto does not.

Any thoughts?

 

[Buddha.]

In the auto position the front axle will engage but the transfer case stays in 2wd until slip is detected
That being said the noise could still be coming from any of the 4wd components I think. Have you checked fluids and checked for grease fittings on the driveshaft?

 

[thebmrust]

In the auto position the front axle will engage but the transfer case stays in 2wd until slip is detected
That being said the noise could still be coming from any of the 4wd components I think. Have you checked fluids and checked for grease fittings on the driveshaft?

Fluids & grease checks are on tap for this weekend.