8-97167406-0 OEM Fit Clutch Master Cylinder Assembly Aluminum Housing 19.05 mm Bore for ISUZU NKR55 NPR 4JB1

The Clutch Master Cylinder with OEM numbers 8-97167406-0 and 8-98117644-0 is a verified direct-fit replacement for ISUZU NKR55 / NPR / NQR / NHR / ELF / 600P series trucks equipped with 4JB1 / 4HK1-T / 4JG2 / 4HF1 / 4BE1 diesel engines. This master cylinder is the core pressure-generating device of the clutch hydraulic control system, converting the mechanical force from the driver's clutch pedal into hydraulic pressure. That pressure is transmitted through the hydraulic line to the clutch slave cylinder (or booster), driving the clutch release fork to disengage and engage the clutch.

The clutch master cylinder is mounted on the engine bay firewall or clutch pedal bracket and is connected to the clutch pedal via a push rod. When the pedal is depressed, the push rod pushes the master cylinder piston, pressurizing the brake fluid (clutch fluid) and delivering it through the outlet port to the clutch slave cylinder. The master cylinder incorporates inlet and outlet valves (check valves) to ensure one-way fluid flow and replenishment from the reservoir when the pedal is released.

The 8-98117644-0 master cylinder features an aluminum housing for lightweight construction and good heat dissipation, with a bore size of 19.05 mm (3/4 inch), precisely matched to the MSB5S transmission clutch system used with the 4JB1 engine. Some variants (such as those for the 4HK1-T) have a 24 mm bore — the bore size must be confirmed against the original component before ordering.

Replace the clutch master cylinder when any of these symptoms appear:

• Spongy or sinking clutch pedal — worn internal piston seals cause fluid bypass, abnormally increasing pedal travel and preventing clutch disengagement.
• Clutch fluid leakage — visible fluid traces at the cylinder housing, push rod dust boot, or line connections.
• Difficulty engaging gears or gear grinding — insufficient hydraulic pressure prevents full clutch disengagement, making smooth gear engagement impossible.
• Clutch pedal does not return or returns slowly — internal piston binding or return spring failure.
• Darkened or contaminated clutch fluid — degraded internal seals contaminate the hydraulic system.

1. Preparation: Disconnect the battery negative terminal. Drain the clutch fluid reservoir with a syringe. Clean the master cylinder and surrounding line connections.
2. Removal: Disconnect the clutch hydraulic line from the master cylinder. Remove the clevis pin connecting the clutch pedal to the push rod. Remove the master cylinder mounting bolts and withdraw the old unit.
3. Inspection: Inspect the firewall or pedal bracket mounting surface for cracks or deformation. Check the hydraulic line for corrosion or blockage. Verify the new master cylinder push rod length matches the original.
4. Installation: Install the new master cylinder onto the bracket and torque the mounting bolts to specification. Connect the hydraulic line. Connect the pedal to the push rod with the clevis pin.
5. Filling & Bleeding: Fill the reservoir with fresh DOT 3 or DOT 4 brake fluid. Bleed the clutch hydraulic system thoroughly (expel air from the slave cylinder bleeder screw).
6. Pedal Test: Pump the clutch pedal several times to verify a firm pedal. Check for leaks at all connections.
7. Road Test: Perform a road test at low speed to verify proper clutch engagement and disengagement.

• Every 10,000 km: Check clutch fluid level and condition. Inspect master cylinder and lines for leaks.
• Every 40,000–50,000 km: Check clutch pedal free play. Inspect push rod and clevis for wear.
• Every 2 years: Replace clutch fluid and thoroughly flush the hydraulic system.
• When spongy pedal or hard shifting is detected: Inspect master cylinder, slave cylinder, and hydraulic system sealing immediately.

• Standard Packaging: Sealed bag + moisture barrier + neutral carton.
• Custom Packaging: Neutral box, color box, or customer-branded packaging.
• Suitable For: Clutch system repair shops, ISUZU parts distributors, fleet maintenance centers.
• Supply Capacity: Stable batch supply with batch-level quality reports available.
• MOQ: Small quantities accepted (quantity discounts available).