2005–2009 Honda TRX400EX/TRX400X ATV Service Manual

This Honda service manual covers maintenance, troubleshooting, and repair for TRX400EX and TRX400X ATVs. It includes system-specific service information, component inspection criteria, assembly illustrations, and workshop procedures.

• Engine repair: Step-by-step procedures for engine removal, cylinder-head disassembly, valve-guide replacement, valve-seat refacing, piston inspection, and camshaft installation.

• Clutch and transmission: Clutch disassembly, gearshift-linkage service, reverse-system inspection, crankcase separation, transmission rebuilding, and crankshaft/balancer installation.

• Fuel and lubrication: Carburetor overhaul, pilot-screw adjustment, high-altitude settings, oil-pump inspection, and oil cooler, tank, and pipe service.

• Wheels, suspension, and steering: Wheel-hub bearing replacement, suspension-arm service, steering-shaft inspection, rear-axle removal, swingarm bearings, and shock-linkage repair.

• Hydraulic brakes: Front and rear master-cylinder and caliper rebuilding, brake-pad replacement, disc inspection, parking-brake adjustment, and fluid replacement/air bleeding.

• Electrical diagnosis: Charging-system troubleshooting, ignition peak-voltage tests, starter-motor rebuilding, switch and diode checks, and wiring diagrams with wire-color abbreviations.

Written for qualified professional technicians, this manual assumes service training and access to the required tools and workshop equipment.

Engine, Clutch, and Transmission Repair

The engine chapters go beyond removal and installation. They cover rocker-arm inspection, decompressor disassembly, valve-guide replacement and reaming, valve-seat contact checks, piston-ring inspection, and cam-chain timing. Standard dimensions and service limits accompany the component checks.

The manual distinguishes work that can be done with the engine installed from transmission and crankshaft service, which requires engine removal and crankcase separation. Transmission assembly illustrations identify the mainshaft, countershaft, reverse-idle gear, shift forks, and washer arrangements; crankshaft installation includes balancer timing references.

Clutch troubleshooting connects symptoms such as slipping, creeping, and hard shifting with cable adjustment, oil condition, and internal wear. Gearshift-linkage drawings and the Reverse System illustration explain how the assist cable, stopper shaft, shift drum, and reverse switch interact.

During decompressor service, supporting the camshaft by its sprocket flange can crack or break that flange. The manual identifies the support points used for this operation.

Carburetor and Dry-Sump Lubrication

Carburetor procedures cover the air cut-off valve, accelerator-pump diaphragm, throttle linkage, float valve, and jets. The Carburetor Assembly exploded view shows their relationship, while the idle-drop procedure explains pilot-screw adjustment after replacement.

Float-level inspection is included, but the float level itself is not adjustable. High-altitude instructions also explain why a modified carburetor must be returned to its standard configuration for lower-altitude operation.

The Lubrication System Diagram traces the oil tank, cooler, pump, filter, and strainers. Oil-pump disassembly includes relief-valve checks and rotor-clearance measurements; maintenance instructions distinguish oil quantities after draining, filter replacement, and disassembly.

Dry-sump oil-level checks specify warm-up conditions because throttle blips can distort the reading. Installing the oil filter backward can cause severe engine damage.

Chassis, Brakes, and Service Access

Chassis coverage includes front suspension pivot bearings, tie-rods, steering-shaft bearings, the rear-axle bearing holder, swingarm pivots, and shock-linkage bearings. Shock-absorber work covers removal, inspection, pivot-bearing replacement, and installation; damaged damper units are handled by assembly replacement.

Brake chapters detail piston and bore inspection, seal replacement, caliper slide-pin assembly, and the rear parking-brake mechanism. Follow the manual’s precautions for brake-fluid handling, vehicle support, and brake-operation checks.

Frame, body-panel, fuel-tank, and exhaust procedures provide access information for larger jobs. Cable & Harness Routing drawings and the crankcase-emission-control illustration help identify hose and cable connections during reassembly.

Electrical Tests and Fault Isolation

Charging, ignition, and starter chapters combine system diagrams with component tests. Ignition diagnosis compares measurements at the ignition control module and the source component, helping distinguish a harness fault from a faulty coil or pulse generator before parts are selected.

The wiring diagram includes connector outlines, switch-continuity charts, and wire-color abbreviations. Separate troubleshooting charts address hard starting, power loss, poor idle, high-speed performance, and handling problems.

Examples of Valve and Carburetor Specifications

Valve-clearance data specify 0.10 mm intake and 0.12 mm exhaust clearance with the engine cold, below 35°C/95°F. Cylinder-head installation specifies a final nut torque of 44 N·m (32 lbf-ft) with oil-lubricated threads and seating surfaces, within a staged crisscross tightening procedure.

Standard QB11A carburetor specifications list a #148 main jet and #38 slow jet. Separate high-altitude instructions distinguish modified jetting and pilot-screw settings from this standard configuration.

Printable PDF with Chapter Bookmarks

Search, navigation, and wiring detail: PDF text search is not available. Embedded bookmarks link to the contents and numbered sections. Small wire-color codes and connector labels in the wiring diagram require zooming.

Supplied as one printable English-language PDF with 345 pages, including four opening pages—cover, safety information, contents/user guide, and symbols—and eight memo pages.