Gearcase and Transfer Case Fluid Change

[AXE]

I decided to change the gear case and transfer case fluid on my ZR2 and wife's Tahoe. They are both coming up on 3 years of service but ZR2 only has 17k miles and Tahoe 25k, so not a lot.

The transfer case and rear differential fluid on the ZR2 looked more used than the Tahoe, probably cause I like to rip it and offroad it a bit. The transfer case fluid was OK, but it was starting to change color to a darker maroon color so I am glad I changed it. The differential fluid still looked decent, but the magnet was pretty full. The front differential was pretty clean and probably didn't need to be changed.

The real PIA, is there are no drain plugs on the ZR2, so you have to pull the whole covers off to drain them.

They have so much red thread locker on the rear bolts, that I could barely get them loose without rounding the shitty soft tiny 10 mm bolt heads. Ended up using a nut extractor on one of them.

The front differential didn't appear to have red thread locker, but they were hard to get out too. Also hard to reach the upper bolts cause the wires for the electric power steering rack are in the way.

I thought it was gonna take a couple hours for both, but with those covers it took about 4 hours. The transfer case was easy, but you have to pull skids for that and the front differential. The Tahoe was significantly easier with the drain bolts and easier access.

 

[AXE]

Bought the fluids on Black Friday and saved about $50 for enough for my 2500HD too. I went with Valvoline cause it didn't seem like Mobil 1 was readily avaliable and it wasn't on sale.

DEX VI ATF for the transfer cases and 75w90 for the gear cases. Here's what I used in the gallon jugs.

 

[AXE]

I have a few different transfer pumps, but decided to buy this 3L jug that comes with several attachments for different applications. You pump it up with air by hand and it has a ball valve to control flow, kind of like a weed sprayer. It was really worth the $25 on Amazon as it just filled the cases with no effort or mess.

Should make work on my sxs easier too.

 

[AXE]

Here's what the inside of the rear locker looks like, as well as the cover. The magnets and cover were pretty dirty with fine sludgey metal, but overall it was really clean inside with just a little grayish film on the gears if you wiped it with a white rag.

The cover is easy to clean with a little wipe down and some degreaser. The gasket can be reused if you're careful to clean it and torque it properly during install. I used a razor blade to clear some leftover material from the outer edge of the mating surface.

 

[AXE]

I don't know who makes these axles for GM, but they really screwed the pooch by not having drain plugs with magnets. There is the same flat spot in the bottom of the bell housing that every differential has. It could have been machined and tapped easily to make those a 20 minute job instead of a 1 hour mess.

Obviously with the lockers you need a cover to make repairs, but you sure as hell don't to change fluids.

I swear these MFers hate us more every time they run out a new model.

 

[LSnTX]

Did you thread lock them again or just torque them to spec?
I think no drain plug for a rig that’s supposed to be in rough environment would be the easy button, but then…

 

[AXE]

Did you thread lock them again or just torque them to spec?
I think no drain plug for a rig that’s supposed to be in rough environment would be the easy button, but then…

I decided not to add thread locker. At that point, some of the gear oil was on the bolts and inside the holes, so I figured it wouldn't work very well anyway. I did clean the bolts and holes with a rag best I could.

They say 15 ft lbs +15 degrees of additional rotational turn. I did 15 ft lbs in cross pattern, then did 20 foot lbs around the horn. It seemed like the right amount for the gasket. Will keep an eye on it.

 

[AXE]

Also loosen the top bolts first and work your way down as itll start to drain on the bottom bolts right away. It's kind of messy, so just loosen them enough and then let it drain. Then finish it up after its empty. Make sure you have a long handle ratchet, at its hard to reach the top bolts. The spare tire on the rear makes it tight too.

 

[scubatech]

It looks like GM still uses the "C", clip style axles. They call it a 12 bolt, but it has smaller bearing than the old ones used to in Chevelle's, etc. My friend and i used to have a side business building differentials years ago. Most people don't even change diff oil. Way to go! That oil can boil under heavy towing!

 

[ZR2xBIZON]

Good write up @AXE I'm looking to change my diff and transfer case fluids this coming week. I normally have the stealership do the maintenance but until I find a better service department, I will be doing it my self

 

[AXE]

Good write up @AXE I'm looking to change my diff and transfer case fluids this coming week. I normally have the stealership do the maintenance but until I find a better service department, I will be doing it my self

Check out the Valvoline prices, I think its still listed as "on sale". Autozone had it discounted. Walmart is usually good and the ATF is listed for $6.88 a quart right now, you'll need two. O'Reilly is out of it's mind, they wanted $14 quart for the ATF and $21 quart for gear oil.

I think with the offroading you do, it is a good idea. I was surprised how my transfer case fluid looked compared to the Tahoe with 8k more miles. Diff fluid was about the same on both rears. Front diffs were still pretty clean.

It'll be interesting to see how your front looks with the harder 4x4 use. My 4x4 use isn't hard core mostly gravel roads, sand, and some light trails.

 

[ZR2xBIZON]

I'll swing by wally world tomorrow morning to grab some fluids.

I too am interested to see what the fluids look like