Vacuum Brake Booster 8942103050 8-94210305-0 For ISUZU NHR98 NHR JMC 4JA1 — OEM-Grade Master Vac Assembly, 30×26×26cm, 6-Month Warranty

The Vacuum Brake Booster with OEM references 8942103050 / 8-94210305-0 is a verified direct-fit replacement for ISUZU NHR98 light trucks equipped with the 4JA1 (2.5L) diesel engine, with cross-platform coverage extending to JMC applications using the same engine family. This assembly is the vacuum-assisted servo unit (Master Vac Assembly) that multiplies driver pedal force to reduce braking effort, mounted in the engine compartment and bolted to the brake master cylinder.

The booster operates on vacuum generated by the engine intake or a vacuum pump, using a pressure differential across an internal diaphragm to amplify pedal input. On the 4JA1 diesel engine — which does not produce intake manifold vacuum in the same way as a gasoline engine — a functioning booster is essential. Without it, pedal effort becomes extremely high and stopping distances increase dramatically, a critical safety concern for a loaded commercial light truck. This unit is supplied as an OEM-grade aftermarket assembly with a reference actual size of 30 × 26 × 26 cm, packaging size of 24.5 × 24.5 × 24.5 cm, and a 6-month quality guarantee.

• Product Type & OEM Description Verified: Confirmed as "MASTER VAC ASM; BRK" (Brake Master Vac Assembly) for ISUZU NHR98 SD KY applications, with 8-94210305-0 listed as the factory number and 351010012 / 8942103050 as the primary OE reference.
• Dimensions Verified: Actual size 30 × 26 × 26 cm; packaging size 24.5 × 24.5 × 24.5 cm — confirmed across multiple Yishan Auto Parts language portals (Slovenian, Spanish, Russian).
• Engine & Vehicle Coverage Verified: Confirmed for ISUZU NHR98 SD KY and JMC applications with the 4JA1 engine model.
• Warranty Verified: 6-month quality guarantee — confirmed by factory supplier data across multiple listings.
• Cross-Reference Density Verified: 8942103050, 8942103051, 8-94210305-0, 8-94210305-1, 8-94210305-SY, 351010012 are consistently grouped as interchangeable/related references across multiple independent supplier catalogs.

• Hard brake pedal / excessive pedal effort: The most common symptom. The booster no longer amplifies pedal force, requiring heavy stomping to stop the vehicle — especially noticeable at low engine speeds or during repeated braking.
• Hissing or air-leak noise from the booster area: A ruptured diaphragm or failed check valve allows vacuum to escape, producing a persistent hissing or "fsss" sound from the engine bay or under the dashboard.
• Longer stopping distance / delayed brake response: Insufficient vacuum assist means the brakes engage later and with less force, extending stopping distances — a critical safety concern for a loaded NHR light truck.
• Brake pedal does not return quickly: A booster with internal valve damage can prevent the pedal from returning promptly, affecting drivability.
• Intermittent power assist loss: Vacuum leaks can cause the assist to fade after the first pedal application, requiring repeated pumping to maintain braking force.
• Rough idle or engine stumble when braking: A failed booster diaphragm can allow unmetered air to enter the intake manifold, disrupting idle quality on the 4JA1 diesel.

• "Booster" vs. "Vacuum Pump" — component scope must be confirmed first: This is the vacuum brake booster (Master Vac Assembly) that amplifies pedal force. It is not the vacuum pump that generates the vacuum supply. Compare the original unit's physical form — a large diaphragm housing vs. a smaller independent pump body — before ordering.
• 8942103050 vs. 8942103051: The -0 and -1 suffixes are grouped as functionally interchangeable for the same booster position on the NHR98 platform. Read the original unit's marking where possible, and confirm the shipped reference matches the ordered reference.
• 8-94210305-SY is the factory number: This denotes the factory tooling reference for the same booster, not a different component.
• Engine and model scope: The confirmed application is NHR98 with 4JA1. While JMC coverage exists, confirm the engine code and VIN before ordering for fleet applications where mixed models may exist.

1. 1Confirm the required component first: Verify that the original unit is the vacuum booster (Master Vac Assembly), not the vacuum pump. Compare the physical shape and diameter.
2. 2Safety first: Park on level ground, engage the parking brake, and chock the rear wheels. Disconnect the battery negative terminal.
3. 3Disconnect the vacuum source and check valve: Remove the vacuum hose from the booster check valve. Note the orientation for reassembly.
4. 4Disconnect the master cylinder: Unbolt the master cylinder from the booster. Support the master cylinder to avoid stressing the brake lines. Plug the lines if fully removed.
5. 5Remove the clevis pin from the brake pedal: From inside the cabin, remove the clevis pin connecting the booster pushrod to the brake pedal arm.
6. 6Remove the booster mounting bolts: From the engine bay, unbolt the booster from the firewall or pedal bracket. Extract the booster carefully.
7. 7Transfer components: If the original booster carries a check valve, gasket, or boot that is not included with the replacement, transfer it to the new unit.
8. 8Install the new booster: Position the 8942103050 booster onto the firewall. Install the mounting bolts and torque to specification.
9. 9Reconnect the pushrod and master cylinder: Reconnect the clevis pin to the brake pedal. Reattach the master cylinder to the booster and torque the mounting nuts to specification.
10. 10Reconnect the vacuum hose and check valve: Ensure the check valve is oriented correctly and the hose is fully seated.
11. 11Bleed the brake system (if hydraulic lines were opened): Bleed the brakes according to the ISUZU procedure until clear, bubble-free fluid flows.
12. 12Test operation: With the engine running, depress the brake pedal and verify that assist is present (pedal should be noticeably easier to press than with the engine off). Check for hissing noises that would indicate a vacuum leak. Road-test at low speed before returning the vehicle to service.

• Inspect the booster vacuum hose and check valve at every brake service or every 20,000–30,000 km — a cracked hose or stuck check valve can mimic booster failure.
• Check for pedal feel changes during routine driving — a progressively hardening pedal indicates declining booster performance.
• Replace the booster at the first sign of hissing, hard pedal, or delayed assist — do not "monitor" a known-failing safety component on a commercial light truck.
• Confirm the diaphragm diameter if replacing the booster — substituting a different diameter alters braking feel and performance.

• Standard packing: Neutral carton with protective internal cushioning; bulk export pallet available. Packaging size reference: 24.5 × 24.5 × 24.5 cm.
• Package contents: 1 × Vacuum Brake Booster (Master Vac Assembly). Master cylinder, check valve, vacuum hose, and mounting hardware may or may not be included — confirm exact package contents at inquiry.
• Set options: Booster only / booster + master cylinder combination (where available) — specify at inquiry.
• Suitable for: ISUZU NHR98 / NHR brake system repair shops, JMC 4JA1 service providers, light commercial fleet maintenance departments, spare parts distributors, and export wholesalers serving Southeast Asia, the Middle East, Africa, and Latin America.
• Related parts available: Brake master cylinder, vacuum check valve, vacuum hose, brake fluid, and complete NHR98 brake system service kits.