If a standard excavator has lost swing torque and swing speed, a worn SY850 Swing Reduction Gearbox is the most common cause. The reduction gear set is the highest load point in the swing circuit, so any slack in the bearings shows up immediately as noise, heat and lost speed. RITO keeps this SY850 Swing Reduction Gearbox in stock as a sealed, pre-assembled replacement.
Item NO.:
SY850Order(MOQ):
1pcsPayment:
T/T, WESTERN UNION, CHINESE BANK,PAYPALProduct Origin:
JAPANShipping Port:
Huangpu,GuangzhouLead Time：
In StockThe SY850 Swing Reduction Gearbox is designed for the load profile of standard excavators working in construction and quarry duty. Torque passes from the motor spline through two or three planetary stages into the output shaft, and each stage is shimmed to a controlled end float so the gear mesh stays aligned under shock loads. Housings are machined on CNC centres to keep bore alignment within tolerance, and each unit is pressure tested for leaks.
| Part Number | SY850 |
| Part Name | Swing Reduction Gearbox |
| Compatible Brand | Sany |
| Applicable Models | SY850 |
| Application | Excavator swing reduction unit in the upper structure swing circuit |
| Material | Cast iron housing with hardened alloy steel gear set |
| Product Color | Industrial grey / OEM color |
| Working Temperature | -25°C~+80°C |
| Key Function | Turns motor torque into controlled swing rotation |
| Condition | 100% New |
| Packaging | Wooden Case Reinforced Carton Neutral Packing Customized Box |
 | Factory Preload Bearings are shimmed and preloaded on the assembly line, which removes the end float that causes noise and premature wear in field rebuilds. |
 | Double-Lip Sealing A double-lip output seal plus O-ring joints keep abrasive dust out of the oil, the main reason reduction units fail early on demolition and quarry work. |
 | Bolt-On Fitment Mounting pattern, output spline and overall envelope follow the original unit, so the assembly installs with the existing bolts, hoses and guards. |
 | Hardened Internals Gears and shafts are case hardened and ground, giving a tooth surface that resists pitting under the shock loads typical of excavator travel and swing duty. |
Q: How do I confirm this SY850 unit fits my machine?
A: Compare the mounting bolt pattern, the output spline and the overall height against the unit on your machine, and check the model plate. If the numbers differ, send us a photo of the plate and we will confirm the correct variant.
Q: What usually causes these reduction units to fail?
A: Contaminated oil and lost bearing preload. Once dust enters through a worn seal, the bearings loosen, the gear mesh misaligns and the unit starts to whine and overheat within a few hundred hours.
Q: Do I need to adjust backlash after fitting?
A: No. Backlash and bearing preload are set at assembly. Fit the unit, fill with the specified oil grade, and check for leaks after the first few hours of operation.
Q: Is this a complete assembly or just the gear set?
A: It is supplied as a complete reduction assembly - housing, ring gear, planet gears, carriers, bearings, seals and output shaft - so nothing has to be transferred from the old unit.
Q: Which oil should I use after installation?
A: Use the grade listed in the machine service manual for the final drive or swing reduction. Overfilling causes heat; underfilling causes immediate bearing damage, so fill to the level plug.
Q: Can this unit be used as an upgrade on an older machine?
A: Where the mounting pattern and spline match, the later specification can be fitted to earlier machines. Confirm the interface dimensions with us before ordering.
Q: Why Choose RITO?
A: Listed Factory
Stable&Reliable Quality
OEM Factory for Chinese Top Excavator Brands
Supplier to Fortune 500 Companies
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