So this blazer is pissing me off. it is a 2002 ZR2. Last year at the end of the winter I posted about a grinding noise in the front end somewhere while driving. 4x4 worked fine then one day it just stopped working. I am assuming the front differential. I drained the front differential like suggested and the fluid looked old and burnt but no metal shavings or chunks. There was not a lot of fluid in it when drained. I would say around half full or so. I know it has a seal leaking as I can see fluid on the differential. I will replace the seal once this 4x4 problem is fixed.

So I replaced with brand new gear oil and now when I try to put it in 4 lo or hi, the 4x4 lights just blink but does not lock the front differential. When in 4 lo the rear differential is definitely in 4 lo because of how it runs. Can't go very fast and super jerky like normal. I hear clicking in the passenger floor board when I select 4x4 and I checked the vacuum actuator under the battery and it appears to be working. When 4x4 is pushed, the actuator fully pulls in and when selected back to 2 wheel drive it goes back out.

I have driven at least 2000 miles since the grinding noise happened and I have not heard it since I replaced the fluid. Could it still be the front differential is bad or could it be something else? It runs fine in 2 wheel drive. I would just hate to throw a new front differential in it and the 4x4 still not work. What does everyone suggest? It has been a good truck except for this damn 4x4 problem. Damn Chevy's. lol