I once worked for several years in a large state-owned enterprise, mainly engaged in the repair of imported on-road and off-road trucks, so I have some experience in truck maintenance. (Repairing loaders, however, belongs to the construction machinery field. I haven’t really repaired domestic loaders — except once, when a colleague’s Chengdu-30 lost reverse gear and I went to help fix it.) Now, a few words of blunt talk: The failure of your main reducer is due to an inherent structural weakness — it’s not durable by design. The factory used a hypoid gear main reducer designed for automotive applications to cut costs, but this design is not suitable for construction machinery. 1. Design Issues and Working Conditions The working conditions of a loader are very different from those of a truck. Loaders frequently operate in reverse — even if reverse operation time isn’t equal to forward operation, it’s not far off. And reverse operations are almost always under heavy load (e.g., backing up after loading). For the main reducer, this is a severe working condition. The problem is that the hypoid gear main reducer performs poorly when driving in reverse — the driving pinion operates at its mechanical limit under reverse torque. This condition is rare in trucks, where heavy-load forward driving is the primary mode. However, for loaders, heavy-load reverse is a common working condition. (If you disagree, try to name a loader that doesn’t frequently perform heavy-load reversing — haha!) Among reliable brands, almost none use hypoid gear transmissions in loaders. They instead use conventional spiral bevel main reducers, which have much higher load capacity. Although the spiral bevel type has a smaller reduction ratio, that’s compensated by final drive (wheel reduction). As a result, unless a gear is literally broken, these reducers don’t show early wear or overload failure. Brands I’m familiar with — CAT, Komatsu, Kawasaki, etc. — all adopt this approach. 2. Advantages and Disadvantages of Hypoid Gear Main Reducers Advantages: Large reduction ratio. High drive shaft ground clearance can be achieved. Compact structure (but that also means high load concentration). Suitable for high-speed vehicle operation. Disadvantages: High load on small pinions (large reduction ratio means shorter pinion life — as few as five driving teeth). Large sliding friction during meshing, leading to heat generation. High assembly precision required and needs special lubricants. Since we can’t change the inherent design flaws, let’s focus on what can be improved in assembly and adjustment. 3. Failure Analysis From the failure condition of your gear set, the following can be observed: The drive pinion shows contact at the heel (large end), already at the limit — this indicates improper adjustment and excessive bearing clearance. Severe bearing wear and poor lubrication — leading to gear surface scuffing, planetary gear and differential case wear, and eventual pitting/spalling failure. (This is evident from the full contact shift toward the large end of the pinion.) Low-quality bearings and improper clearance adjustment, causing early failure and subsequent damage to the entire gear set (including planetary and side gears in the differential). 4. My Recommended Technical Approach (Purely from a Technical Perspective) Do not buy OEM bearings (although OEM gears should be used). OEM bearings are decent but not top-tier — cost control affects quality. Instead, use high-precision bearings, at least Chinese old standard E-class or ISO P5 grade. They’re more expensive but have double the lifespan. (A true case from experience: In 1992, when I worked at a state enterprise, an electrical technician asked me to diagnose a newly overhauled 250 kW synchronous motor that was overheating and noisy. With only a homemade stethoscope, I traced the problem to the bearings. He had unknowingly bought counterfeit bearings. Following my advice, he replaced them with genuine E-class bearings from Harbin Bearing Factory — and the issue was completely solved. That story became well known in our company and taught me the value of cross-disciplinary knowledge — and how to judge bearing quality by simple means.) Repair or replace the differential housing. If it’s excessively worn and not restored or replaced, planetary and side gears will have extremely short life under heavy-duty conditions. The planetary washers will deform and fail from back pressure wear, leading to gear breakage. Since the housing is cast iron, it’s hard to repair and machine properly. During assembly, carefully adjust bearing clearance and gear contact pattern. Within specified limits, smaller bearing clearance means longer life and higher load capacity. (In some precision applications, preload — negative clearance — is even applied so that proper clearance appears under load.) For the gear set, contact pattern should favor the toe (small end) and be slightly toward the top of the tooth when considering reverse load. This way, under heavy load, the contact will move toward the heel and root — the strongest parts of the tooth. This adjustment is more critical than simply meeting backlash specifications. Never heat bearings with an oxy-fuel cutting torch. Your current bearings have been heat-damaged and have very short remaining life. If heating is necessary, use an oxy-acetylene welding torch and move the flame — never heat one spot continuously. A practical temperature guide: when a drop of water evaporates instantly, it’s around 200 °C — a quick “poor man’s thermometer.” Always use reliable hypoid gear oil, rated GL-5, viscosity 85W-140. Preferably choose a trusted brand — even genuine Great Wall (Changcheng) oil is acceptable. Replace it at regular intervals per standard maintenance requirements — after all, changing oil is always cheaper than changing parts.