Product Overview
The 50027484 18V 8-Tooth Motor Assembly is a precision-engineered direct-fit replacement for the RS-550VD-6532 brushed motors used in 18V cordless rotary hammers built on this common platform[reference:7]. This complete motor assembly includes the motor and the 8-tooth pinion gear – eliminating the need for separate gear replacement and ensuring proper gear mesh out of the box.
Designed for professional repair technicians and equipment maintenance specialists, this motor restores factory-spec performance to tools exhibiting sluggish operation, complete failure to start, or loss of hammering action under load. The 18V DC brushed motor delivers consistent torque for demanding hammer drilling applications into concrete, masonry, and other hard materials[reference:8].
Built with a robust metal housing and quality brushed internals, this 550-series motor delivers consistent torque and extended life even under frequent use[reference:9]. The 8-tooth pinion gear with approximately 7.7mm tooth pitch ensures smooth coupling and reliable power transfer in demanding drilling applications[reference:10].
💡 Pro Tip – Pre-Installation Diagnostic: Before replacing the motor, perform a simple test. With the battery removed, rotate the output shaft by hand. A smooth rotation indicates the gear train is intact. Any grinding, binding, or uneven resistance points to gear damage – not the motor. If the motor spins freely but the tool fails to run under power, the issue is likely electrical (trigger, controller, or battery contacts). Always remove the battery pack before beginning disassembly.
Diagnostic & Fitment – When to Replace
Specification Comparison
| Specification | Worn / Generic Aftermarket | FixPartHub Precision Replacement ✅ |
|---|---|---|
| Motor Type | Generic – unknown specifications | RS-550VD-6532 – OEM-spec brushed motor[reference:11] |
| Pinion Gear | Inconsistent tooth count or pitch | 8 teeth – 7.7mm pitch[reference:12] |
| Housing Material | Lightweight plastic – prone to damage | Robust metal – extended durability[reference:13] |
| Voltage Rating | Vague or incorrect rating | 18V DC – OEM specification |
| Compatibility | Vague or incorrect fitment claims | WU390 / WX390 / WX390.1 – direct-fit guaranteed[reference:14] |
Teardown & Replacement Workflow
Compatibility – Cross-Reference & OEM Part Numbers
Diagnostic Q&A
❓ Q: My rotary hammer runs slowly but still works – is this definitely a motor problem?
A: Not always. First, test with a fully charged battery – weak batteries can mimic motor failure. Clean the battery and tool contacts with an eraser. If the problem persists, the motor brushes are likely worn. The 50027484 motor assembly includes both the motor and the 8-tooth pinion gear – replacing the entire assembly addresses both motor and gear wear simultaneously.
❓ Q: What is the difference between 50027484 and other motor part numbers for this platform?
A: 50027484 is the OEM part number for the complete motor assembly used in WU390, WX390, and WX390.1 rotary hammers. It is specifically the RS-550VD-6532 motor with an 8-tooth pinion gear[reference:15]. This is the correct motor for these brushed models – not to be confused with brushless motor assemblies used in newer tool variants.
❓ Q: Does this motor include the pinion gear or do I need to purchase it separately?
A: This is a complete motor assembly that includes the 8-tooth pinion gear with approximately 7.7mm tooth pitch[reference:16]. No additional gear components are required – the motor installs as a single unit with the pinion gear already installed on the output shaft.
❓ Q: Will this motor fit both the WU390 and WX390 models?
A: Yes. The 50027484 motor assembly is compatible with WU390, WU390.9, WX390, and WX390.1 models[reference:17][reference:18]. The motor and 8-tooth pinion gear are identical across these variants – the difference is in the hammer mechanism and housing, not the motor.
Safety Notes
- 🔴 Always remove the battery pack before beginning any disassembly or motor replacement procedure.
- ⚡ Allow the tool to cool completely before handling internal components – motors can reach high temperatures during hammer drilling operations.
- 🔧 Use correct torque values – housing screws typically require 0.8–1.2 Nm (7–10 in-lbs). Over-torquing can strip housing threads or crack the plastic housing.
- 🧤 Wear ESD-safe gloves when handling the motor assembly to prevent static discharge damage to sensitive electronic components.
- 📐 Verify gear mesh before final assembly – the pinion gear should engage smoothly with the transmission gears with no binding.
- ✅ Perform a no-load test before full reassembly – insert battery and verify smooth operation in both drill and hammer modes.
A: First, test with a fully charged battery. Clean the battery and tool contacts with an eraser. If the tool still runs sluggishly or fails to start, listen for unusual noises or check for excessive heat during operation. If the motor runs but the tool lacks power, the motor brushes are likely worn – requiring replacement of the 50027484 motor assembly.
A: Yes. The 50027484 motor assembly is compatible with WU390, WU390.9, WX390, and WX390.1 models. The motor and 8-tooth pinion gear are identical across these variants.
A: Yes. This is a complete motor assembly that includes the 8-tooth pinion gear with approximately 7.7mm tooth pitch. The motor installs as a single unit with the pinion gear already installed on the output shaft – no additional gear components are required.
A: This is an 18V DC brushed motor, specifically the RS-550VD-6532 model. It delivers consistent torque for hammer drilling into concrete, masonry, and other hard materials.
