Solid Axle Upgrade
The H3 Hummer has a solid AAM 860 axle in the rear of the vehicle that is commonly referred to as the GM 8.6. This axle that all H3 Hummers come equipped with from the factory is very well suited for the off-road application and hold up quite well. However the axle does have a partial flaw. The differential cover that seals the ring and pinion off from dirt and debris is not capable of supporting the weight of the vehicle, which can happen off-road. Underneath the differential cover is some of the most important parts of any vehicle, the ring & pinion, the spider gears, bearings, and also axle shafts. Those part turn the torque from the motor 90° and transferred onto the tires. This process of turning the torque 90° require a lot of precision to work properly. Being off even just a 1/16 of an inch can cause major problems. This is why I needed to protect my AAM 860 axle with an aftermarket heavy duty differential cover.
Being a fan of company Solid Axle Industries, I decided to go with their solution for protecting my AAM 860 solid axle. Even though the company Solid Axle doesn’t sell heavy duty differential cover for AAM 860, they do have a product for the GM corporate 10 bolt cover which is also another name for the AAM 860. The heavy duty corporate 10 bolt cover is made from cast iron 3/8 inch thick and reinforced with thick nodular bracing, literally making the AAM 860 bullet proof.
Installing the Solid Axle differential cover on the H3 Hummer is for the most part straight forward, but I do have some recommendations before starting this project. While swapping the diff covers absolutely no dirt can get inside the axle housing, is very important. The bolts that Solid Axle Industries are shipped in the box are not long enough and forced me to buy 10 new bolts 5/8 course thread bolts with 1 inch of threads, this is approximately 1/4 longer than theirs. The owners manual mentions that the 3 litters of 75w-90 oil needs to meet the GM specification 9986115, however the local NAPA auto parts said that any modern day off the shelf synthetic 75W-90 with or without the limited slip additive will work just fine. The mounting bracket for the brake line uses one of the ten bolts holding on the differential cover on and because of the extra thickness of the diff cover it will not bolt up. I used my grinder to shave off approximately a 1/4 of metal from the outside to make it fit with no problems, which I show in one of the images above. Finally, pouring the 75W-90 oil into the differential is rather difficult because of where the sway-bar is located. Some ingenuity, with the combination of jacking the Hummer up and a hose I was able to pour the oil into the axle.