Just wanted to share some information I found out on my ’21 Silverado front and rear axles. Seem like for at least 2019 thru 2021 for GMC and Chevy half tons, there were two differential axle manufacturers. AAM (American Axle Manufacturing) and GM.
AAM axles were supplier A RPO SU4 front axle, RPO SU7 the rear.
GM axles were supplier B RPO SU5 front axle, RPO SU8 the rear.
These axles look different and the easiest way to identify, for me, was to look at the axels. The GM rear has the GM emblem stamped on the bottom of the differential housing. The front axle the same GM mark of excellence symbol stamped near the output shaft. It was very easy to locate these markings.
The AAM axles call for AC Delco 10-4091 (GM 19300457) 75W85; High Efficiency; Synthetic Hypoid Gear Oil. This a GL-5 oil.
The GM axles require AC Delco 10-4122 (GM 19368514) 75W85 Dexron Low Viscosity Gear oil. This is a GL-4 oil. A new formulation not like yester years GL-4.
Best I can tell this is accurate from my online research. I tow with this truck and wanted to find out before hand what gear oil I would need when I decide to change it and found out about the two different axel suppliers. In the grand scheme it may not make any difference as aftermarket gear oil suppliers seem to list only one oil for the models. However Rock Auto does show different AC Delco oils for each axle supplier. Hopefully this may help someone in a similar situation.
AAM axles were supplier A RPO SU4 front axle, RPO SU7 the rear.
GM axles were supplier B RPO SU5 front axle, RPO SU8 the rear.
These axles look different and the easiest way to identify, for me, was to look at the axels. The GM rear has the GM emblem stamped on the bottom of the differential housing. The front axle the same GM mark of excellence symbol stamped near the output shaft. It was very easy to locate these markings.
The AAM axles call for AC Delco 10-4091 (GM 19300457) 75W85; High Efficiency; Synthetic Hypoid Gear Oil. This a GL-5 oil.
The GM axles require AC Delco 10-4122 (GM 19368514) 75W85 Dexron Low Viscosity Gear oil. This is a GL-4 oil. A new formulation not like yester years GL-4.
Best I can tell this is accurate from my online research. I tow with this truck and wanted to find out before hand what gear oil I would need when I decide to change it and found out about the two different axel suppliers. In the grand scheme it may not make any difference as aftermarket gear oil suppliers seem to list only one oil for the models. However Rock Auto does show different AC Delco oils for each axle supplier. Hopefully this may help someone in a similar situation.