Vacuum Brake Booster 8-94342428-1 8943424281 For ISUZU TFR TFS Pickup 4JA1 4JB1 1988–1991 1995–2002 — 9-Inch Single Diaphragm, Master Vac Assembly, OEM-Grade Aftermarket

The Vacuum Brake Booster with OEM reference 8-94342428-1 / 8943424281 is a verified direct-fit replacement for ISUZU TFR and TFS pickups across two production windows: 1988–1991 and 1995–2002. This assembly is the vacuum-assisted servo unit that multiplies driver pedal force to reduce braking effort. It mounts in the engine compartment and bolts to the brake master cylinder.

Catalogued under the ISUZU OEM description "MASTER VAC ASM; BRK" (Master Vacuum Assembly; Brake), this is a 9-inch diameter single-diaphragm booster — the standard configuration for the TFR/TFS light pickup platform.

The booster operates on engine vacuum (or vacuum pump supply on diesel variants), using a pressure differential across an internal diaphragm to amplify pedal input. On the 4JA1, 4JB1, and 4JG2 diesel engines used in the TFR/TFS, 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 pickup. This unit is an OEM-grade aftermarket assembly, with reference packaging dimensions of approximately 24 × 24.5 × 24.5 cm and a 6-month quality guarantee from the supplying factory.

• Product Type & OEM Description Verified: Confirmed as "MASTER VAC ASM; BRK" (Brake Master Vac Assembly) for the ISUZU TFR platform, with 8-94342428-0 listed as the factory number and 8943424280 / 3510100D as the primary OE reference in supplier catalogs.
• Diameter Verified: 9-inch (9") — confirmed by a Guatemala-based ISUZU parts supplier listing the 8-94342428-1 booster for TFR/TFS 1988–1991 and 1995–2002 with "DIÁMETRO 9".
• Vehicle Coverage Verified: Confirmed for ISUZU TFR/TFS Pickup, with two production windows: 1988–1991 and 1995–2002. A Saudi parts listing further confirms D-MAX diesel 1988–2003 compatibility for the 8-94342428 family.
• Engine Association Verified: 4JA1 engine model is explicitly listed for the 8-94342428-0 factory number in supplier technical data. The TFR/TFS platform also covers 4JB1 and 4JG2 diesel variants.
• Packaging Dimensions Verified: 24 × 24.5 × 24.5 cm (packaging size) and 24 × 24 × 27 cm (actual size reference) — confirmed by factory supplier data.
• Warranty Verified: 6-month quality guarantee — confirmed by the supplying factory listing.
• Cross-Reference Density Verified: 8-94342428-0, 8943424280, 3510100D, 8943424281, 8-94342-428-1 are consistently grouped as interchangeable/related references across multiple international supplier catalogs.
• Net Weight Not Publicly Disclosed for This Exact Unit: Public listings for 8-94342428-1 do not publish a net weight. A related ISUZU D-MAX booster (8980067880) lists a net weight of approximately 3.6–4.4 kg; the TFR booster is likely in a similar range, but confirm net weight at inquiry for freight planning.

• 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 TFR pickup.
• 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 on vacuum-assisted diesel systems, disrupting idle quality.

• "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.
• 8-94342428-1 vs. 8-94342428-0: The -0 suffix is the factory number most frequently cited in supplier catalogs, while the -1 is the specific OE reference in the user's query and in the Guatemala parts listing. These are functionally interchangeable for the same booster position on the TFR/TFS platform. Read the original unit's marking where possible.
• 9-inch diameter is the defining specification: This booster uses a 9-inch (9") diaphragm. A different diameter booster will alter pedal effort and braking feel. Confirm the diameter against the original unit before ordering.
• Production window split: The TFR/TFS platform spans 1988–1991 and 1995–2002 for this booster reference. Confirm the vehicle's model year and chassis code before ordering, especially for transitional years.
• Engine variants: Supplier data primarily associates this booster with the 4JA1 engine, while the TFR/TFS platform also includes 4JB1 and 4JG2 variants. Confirm the engine code and VIN before ordering for fleet applications.

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 (9-inch).
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 8-94342428-1 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 pickup.
• Confirm the 9-inch specification 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.
• 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 TFR/TFS brake system repair shops, pickup 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 TFR/TFS brake system service kits.