Product Overview
The N279940 Transmission Assembly is a precision-engineered direct-fit gearbox replacement for 20V Max cordless compact drills built on the DCD771 / DCD734 platform. This complete transmission assembly (referenced as “TRANSMISSION SA” in OEM parts diagrams, item 6)[reference:8] is the core component that transfers motor power to the chuck through a two-speed mechanical gear train[reference:9].
Designed for professional repair technicians and equipment maintenance specialists, this transmission restores factory-spec performance to tools exhibiting slipping drive, loss of torque under load, grinding noises, or complete transmission failure. The mechanical two-speed gearing provides 0-450 RPM (low speed) for high-torque driving applications and 0-1,500 RPM (high speed) for efficient drilling[reference:10].
The N279940 transmission assembly is the direct replacement for the original equipment gearbox in DCD771, DCD734, DCD731, DCD776, and related 20V Max compact drill variants[reference:11][reference:12]. It includes the full gear train with integrated speed selection mechanism – no additional gear components are required for installation.
💡 Pro Tip – Pre-Installation Diagnostic: Before replacing the transmission, perform a simple test. With the battery removed, rotate the chuck by hand through both speed ranges. A smooth rotation with positive detent engagement indicates the gear train is intact. Any grinding, binding, or uneven resistance points to gear tooth damage or bearing failure – both resolved by this N279940 transmission replacement. Also inspect the motor assembly (N362741) for wear while the gear case is open[reference:13] – if damaged, it should be replaced simultaneously. Always remove the battery pack before beginning any disassembly.
Diagnostic & Fitment – When to Replace
Specification Comparison
| Specification | Worn / Generic Aftermarket | FixPartHub Precision Replacement ✅ |
|---|---|---|
| Gear Material | Low-grade steel or sintered metal – rapid wear | OEM-spec alloy steel – maximum durability |
| Speed Range | Inconsistent or missing detents | 0-450 / 0-1,500 RPM – positive detents[reference:14] |
| Torque Transmission | Slipping under load – power loss | Full torque delivery – OEM-spec |
| Fitment Guarantee | Vague or incorrect compatibility claims | DCD771 / DCD734 / DCD731 / DCD776 – direct-fit |
| Part Number Status | Generic cross-reference – uncertain quality | Active OEM N279940 – factory specification[reference:15] |
Teardown & Replacement Workflow
Compatibility – Cross-Reference & OEM Part Numbers
Compatible with DCD771 (Type 1, 10), DCD734 (Type 1), DCD731, DCD776, DCD771C2, DCD771N, CMCD701C2, and related 20V Max compact drill variants[reference:16][reference:17][reference:18]. Referenced as item 6 in OEM parts diagrams[reference:19]. Also compatible with DCD734 Type 1 and DCD771 Type 1 platforms[reference:20][reference:21].
Diagnostic Q&A
❓ Q: My drill makes a grinding noise but still spins – do I need to replace the entire transmission assembly?
A: Yes. Grinding noise indicates tooth wear or pitting in the gear train. While the drill may still function, the damage will progressively worsen until the transmission fails completely – often at the worst possible moment. Replacing the complete N279940 transmission assembly now prevents catastrophic failure and potential damage to the motor and other components[reference:22].
❓ Q: What models are compatible with the N279940 transmission assembly?
A: This transmission is compatible with DCD771, DCD734, DCD731, DCD776, DCD771C2, DCD771N, CMCD701C2, and related 20V Max compact drill variants[reference:23][reference:24]. It is referenced as item 6 in OEM parts diagrams for these models[reference:25]. Always verify your tool’s model number against the compatibility list before ordering.
❓ Q: Is N279940 the correct replacement part number for my drill?
A: Yes. N279940 is the active OEM part number for the transmission assembly (TRANSMISSION SA)[reference:26]. It is referenced as item 6 in OEM parts diagrams[reference:27]. This listing supplies the N279940 assembly, which is the correct replacement for all compatible models[reference:28].
❓ Q: What other components should I inspect when replacing the transmission assembly?
A: While the gear case is open, inspect the motor assembly (N362741) for wear[reference:29] – if damaged, it should be replaced simultaneously. Also check the gear (N215913)[reference:30] and the speed selection mechanism for wear. Replace any worn components simultaneously to ensure full transmission performance.
Safety Notes
- 🔴 Always remove the battery pack before beginning any disassembly or transmission replacement procedure.
- ⚡ Allow the tool to cool completely before handling internal components – gear cases can reach high temperatures during operation.
- 🔧 Use correct torque values – gear case screws typically require 0.8-1.2 Nm (7-10 in-lbs). Over-torquing can strip housing threads or distort the gear case alignment.
- 🧤 Wear appropriate PPE – safety glasses and cut-resistant gloves when handling gears and metal components.
- 📐 Verify gear mesh before final assembly – the transmission should shift smoothly between high and low speeds with positive detent engagement.
- ✅ Perform a no-load test before reinstalling the chuck – verify smooth operation in both speed ranges and correct clutch function.
A: Perform a manual rotation test with the battery removed. Rotate the chuck by hand through both speed ranges (high and low). Smooth, consistent rotation indicates the gear train is intact. Any grinding, binding, uneven resistance, or complete seizure indicates gear tooth damage or bearing failure – requiring replacement of the N279940 transmission assembly. Additionally, listen for grinding or whining noises during operation under load – this indicates active tooth wear.
A: Yes. N279940 is the OEM transmission assembly for both DCD771 and DCD734 platforms. It is referenced as item 6 in OEM parts diagrams for both models. This is the correct direct-fit replacement across both models.
A: The N279940 transmission delivers two-speed mechanical gearing: 0-450 RPM (low speed) for high-torque driving applications and 0-1,500 RPM (high speed) for efficient drilling
