Jacob Szymanski

The AAM axle may have a drain, the GM does not.

Haven’t seen much on the forums or YouTube about front differential service on these trucks so wanted to post about it. Everything I have seen recommended to suck the oil fluid out and refill rather than taking the diff cover off due to lack of room to work. I did not like that route, so I pulled the cover and can report there is plenty of room. Here’s how I did it: 1. Remove skid plates 2. Disconnect battery 3. Remove locking clips from the 3 connectors on the power steering rack and then disconnect the 3 connectors and move them out of the way (note: top locking clip is white and hard to reach, I used a bent pick) 4. Disconnect the front 4x4 solenoid connector to get the wire out of the way 5. Loosen fill plug (this is critical so you know you can refill it) 6. Remove all except 2 diff cover bolts, a flex head ratchet was useful here and one bolt needed a wrench. 7. Loosen last two bolts, crack the cover seal, and drain. 8. The diff cover comes out with minimal maneuvering, recommend marking the cover and noting gasket position before removal since it’s relatively symmetrical. 9. Wipe everything out and clean the surfaces. 10. New gasket P/N: 84428297 for GM axle, install and torque bolts to 30 ft-lb 11. I used a hose on the end of the gear oil bottle and went though the wheel well with the tire off to fill the diff easier, can fill the same way from underneath with a pump. 12. Rest is reverse from before. Rear diff is the same but easier, gasket P/N 84412728 for GM axle. I have been using 75W-90 with no LS additive in heavy towing applications with the 3.42 gearset and only have a small amount on the magnet each time with services every 25,000 miles. The rear diff will have clutch material everywhere from the G80 if you use it often so I just wiped that off anywhere I could reach. Lastly, the front diff gear is welded to the carrier, so looks like a regear for our trucks is out of question until the aftermarket makes a front locker/carrier of some kind.

Wanted to post an update to this thread, have had the thermostat out and secondary cooler installed for a whole year and here are some observations: transmission temp on the highway sits around 135 in winter (not super cold here only gets into high 20’s) and 150 in summer (even up to 100°+ outside). City driving gets to around 165°. Have done some off-roading on long, steep service roads and got the secondary cooler to kick on. I’d say I was averaging about 5mph on some really steep grades and the cooler kept the temps down below 200° even with about 1000 lbs of people and equipment in the truck. Likewise with towing I have a 8.5x24 foot car hauler and have had no issues with transmission temps even in traffic. A note for installation: the Derale kit comes with a thermostat that has a tiny thread that is not tapered. You NEED to use a liberal amount of LIQUID TEFLON to get it to seal, or else you will have a drip. Also, injection fuel line style hose clamps are the way to go for these lines as they aren’t under much pressure but these give you peace of mind to prevent a line blowing off from a cracked clamp. DO NOT use the clamps that come with the Derale kit (ask me how I know…). Overall I would highly recommend the upgrade if you do any kind of off-roading or towing as it was cost effective and works great!

Forgot to add, but also had to refill the transmission obviously. Make sure it's nice and level and get a fluid pump but it was quite an easy process that is published readily for the 6l80e.

I noticed my transmission temperature getting quite high when driving on trails or towing through traffic so I decided to add a secondary Derale 13900 transmission cooler in addition to the stock front mounted cooler. My truck is a 2020 Custom TB with the 5.3 and 6 speed 6l80e. This kit came with everything I needed except for a couple fittings, and the fan is wired to an ignition power source so it won't drain the battery. You can see that it is mounted to a winch mount that I had made, but without the winch there that would be a great spot to fit the cooler. Essentially I followed the return cooler line from the transmission forward until the hard lines split off into two rubber lines with the return going to the driver side of the truck. NOTE: The hard lines are 3/8" but the rubber line is 1/2" (learned that the hard way). I first held the cooler in place and measured what angle it needed to sit at and tacked together some mounts, then after a couple of iterations got it to where it fit and the skid plate did not interfere. I then finish welded, drilled, tapped, and painted the mounts. On the cooler itself, I mounted the 180 deg thermostat to the lower connection. With the cooler location determined, I then measured and cut the 3/8" rubber hose in the kit. I then clamped the return rubber line on the truck, cut the rubber hose, and connected the 3/8" cooler hoses to the pre-existing 1/2" hose on the truck. I used one 3/8-1/2 straight barbed connector and one 3/8-1/2 90 deg barbed connector. Some zip ties to tidy up the lines too. Wiring was simple as well, easiest way to get a for sure ignition power source was to get a fuse tap from autozone for a micro2 fuse and then you have a fused ignition source. Ran the power to the thermostat and then positive from motor to the other side of thermostat and the ground to the frame. The hole in the skid plate has an aluminum mesh behind it to keep small rocks out, and it's pretty high up so shouldn't see much abuse. Haven't given it a full test for cooling capability yet but the fan is nice and strong so I have no doubt it'll help. For about $200 total I'd say its a great upgrade for anyone who tows in the city or hits the trails on any steeper terrain.

The original mount was a little weaker than anticipated so I went ahead and added some new supports. Fairlead is much stiffer now.

Finally got around to wiring the winch into the cab. I just spliced into the wiring in the solenoid box and added a couple of grommets as shown in the picture. The arm switch for the winch is the switch for my amber fog lights since I ran out of switches and figured that I'd have those on while winching anyways. This let me keep the option to plug in the normal remote and run the winch outside the truck as well.

Had some time today to clean up the wiring, here’s a great spot to get wires from the engine bay into the cab I wanted to share. Just have to cut a hole in the rubber grommet then I taped it to the corrugated wrap really well. There is another one just like it on the passenger side too. Also decided to wire the winch into the cab on a rocker switch instead of a wireless remote, will post once I get that done.

Also, the solenoid pictured is for a power inverter I have mounted in the tool box in the bed. The other small wires are for some fog lights and ditch lights. I made the mounts for those as well and can send pictures in case anyone is curious about those.

That mount looks awesome! I searched for a long time and did not see anything for these trucks. Let me know if you want to see anything else about the wiring and I’ll be happy to take pictures.