This is something that I like to do at the 50k mile mark on the Envoy. I believe that it is also the recommended interval to change the Transfer Case Fluid in the Envoy, Trailblazer, Bravada, and 9-7. This is not too difficult a job to accomplish as long as you have the required tools to do the job.
So first, let’s talk about the tools that you will need. As always, when working underneath a vehicle, you will need to have a good Hydraulic Jack as well as Jack stands to safely lift and support the vehicle. Make sure you have decent jack stands to support the weight of the Envoy, this is not a cheesy little compact car!
You will also need a fluid pump. I have purchased a manual type pump in the past that I have been using to do this maintenance. The thing with doing this job is that you need to pump the fluid from the bottle to the transfer case; you cannot pour it in since there is no top side access.
A catch can will be necessary to collect the fluid that will be coming out of the Transfer Case.
The last tool that you will need is a size 10 Allen key. This size is sufficient to remove both bolts.
The Envoy also requires special fluid for the transfer case. You will need 2 quarts of Auto Trak II. This is blue fluid, so don’t be alarmed when you see it. This is also not so easy to find and this time around I needed to get it from Amazon. A trip to the dealer only turned up one quart.
Ok, now onto the fluid change!
Jack up the vehicle with your Hydraulic Jack and support it on Jack Stands. Make sure that you use solid points for the jack stands so that it is stable and you don’t damage the truck.
Crawl underneath the center of the vehicle and locate the Transfer Case.
Remove the top bolt from the transfer case. The reason you remove the top bolt first is to make sure that you can get it out. No sense in draining all the fluid if you cannot put it back in!
Top Bolt Location
Top Bolt Removed
Place your catch can underneath the drain plug and remove the drain plug from the transfer case. There will be a really fast rush of fluid that spills out but it is short lived since there is not much fluid in the case.
Bottom Bolt Removed, Draining Fluid
Replace the drain plug once all the fluid is drained.
Connect the fluid pump to the top of the AutoTrak II bottle and put the hose into the fill hole. Pump away until fluid is coming out of the top hole. This should be just shy of 2 quarts. I pumped as much fluid as I could out of both bottles, and then put the fluid from the one bottle into the other and did it again. Once it was almost empty, fluid started leaking out of the top hole.
Replace the fill plug.
Lower the vehicle and you are done!