I just got this truck ('04 silverado 1500 LT 4x4) about a month ago with 150k miles on it. as far as carfax and i know the trans fluid, dif fluid, and transfer case have never been changed. I read in the manual that the trans fluid should be changed every 50k but in my old dodge it wasnt a good idea to change it after 100k...is it the same in chevys? if not then what should i start with trans, dif, or transfer case? Is there a recommended fluid for each or will the regular autozone/advanced auto parts fluid work? I usually use royal purple for the differentials...is there something better/chevy specific that would be better?

 

Check the tranny fluid. If it is brown and has a brown burnt odor - DON'T TOUCH IT!!!

As far as the diffs and trans case, it won't hurt those to change out the fluids. You probably have the limited slip so I believe any good synthetic fluid contains the proper additives. If you have the g80 locker, you may need the posi additive for the rear axle. I'm not sure what the fluid for the trans case is. Check with your local parts store and they can tell you. also the dealer will tell you what you need. With that info, you can buy the equivalent stuff at your local parts store.

 

I checked the transmission fluid a couple weeks ago and honestly it still looked brand new. Didnt smell burnt or anything. It may not need changed but I believe in better safe than sorry when it comes to fluids being as it is a used truck. How can I tell if I have the g80 or not? Or the posi-trac?

 

The absolutely easiest way is to call your local GM dealer and provide them (service adviser not parts department) the vin. They can pull up all the options codes for each truck. you are looking for the option "G80". sometimes, there is a sticker somewhere in the glove box area that will have the options codes. Ur looking for the same code.

 

Sorry, i didn't read your entire post. GM does not offer a true posi rear end for the trucks. Only the G80 mechanical locker that engages when the rear end detects a 100 rpm difference between the right and left tires. When this happens, a cam in the diff will engage and lock up the axle. At approximately 35 -45 mph, centrifugal force disengages the cam and the axle opens up for fuel economy.

Eric