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Product Details
The Honda OEM B-Series Manual Transmission Mainshaft Angular Ball Bearing is a genuine factory replacement designed to provide precise shaft support, smooth rotation, and reliable operation in compatible Honda and Acura 5-speed manual transmissions.
Manufactured to Honda's original equipment specifications, this precision-engineered angular contact ball bearing measures 28mm x 72mm x 18mm and is designed for the rear mainshaft (input shaft) bearing position in applicable B-Series manual transmissions.
Commonly used in vehicles such as the 1999–2000 Honda Civic Si, 1994–1997 Honda del Sol VTEC, and 1992–2001 Acura Integra, this genuine Honda bearing is an excellent replacement for worn or damaged original transmission components.
Unlike a conventional radial ball bearing, an angular contact bearing is designed to accommodate both radial and axial loads. This makes it particularly important in manual transmissions, where rotating shafts must remain properly supported under varying driving conditions.
Over time, transmission bearings can develop wear from high mileage, contaminated transmission fluid, excessive drivetrain loads, or performance driving. A worn mainshaft bearing may contribute to transmission whining, vibration, abnormal shaft movement, and accelerated wear of surrounding gearbox components.
Whether you're rebuilding a B16 or B18 transmission, restoring an original Civic Si or Integra gearbox, or preparing a B-Series drivetrain for a performance build, this genuine Honda OEM Angular Ball Bearing provides the factory-correct dimensions and construction needed for dependable transmission operation.
Features
- Genuine Honda OEM Part: Authentic factory replacement manufactured to Honda's original equipment specifications.
- Angular Contact Ball Bearing: Designed to support combined radial and axial loads within the transmission.
- Mainshaft Bearing Application: Supports the mainshaft/input shaft in compatible Honda and Acura manual transmissions.
- 28mm Inner Diameter: Factory-specified bearing bore.
- 72mm Outer Diameter: Designed to fit the corresponding transmission housing.
- 18mm Width: Maintains the original factory bearing dimensions.
- Direct OEM Replacement: Replaces the original bearing where Honda specifies part number 91004-P21-003.
- Precision Bearing Construction: Helps maintain smooth shaft rotation and accurate component alignment.
- Factory-Correct Fit: Designed for the original bearing location without modification on compatible transmissions.
- Ideal for Transmission Rebuilds: Excellent for B-Series gearbox maintenance, restoration, and complete rebuilding.
- Performance Build Friendly: Suitable for compatible naturally aspirated, turbocharged, and supercharged B-Series drivetrain projects.
- Sold Individually: Includes one genuine Honda angular ball bearing.
- OEM Part Number: 91004-P21-003.
Additional Information
- Manufacturer: Honda / Acura
- Part Number: 91004-P21-003
- OEM Description: Bearing, Angular Ball (28x72x18)
- Other Names: Mainshaft Bearing / Input Shaft Bearing / Rear Mainshaft Bearing / Angular Contact Ball Bearing / B-Series Transmission Bearing
- Product Type: Manual Transmission Bearing
- Installation Location: Rear Mainshaft / Input Shaft Bearing Position
- Bearing Type: Angular Contact Ball Bearing
- Inner Diameter: 28mm
- Outer Diameter: 72mm
- Width: 18mm
- Quantity: Sold Individually (1 Bearing)
Common Reasons for Replacement
Manual transmission bearings should be inspected whenever the gearbox is disassembled for maintenance or rebuilding.
- Transmission whining or abnormal bearing noise
- Rough or noisy mainshaft rotation
- Excessive shaft movement
- Worn or damaged bearing races
- Pitting or deterioration of bearing surfaces
- Contaminated or insufficient transmission fluid
- High-mileage transmission rebuilding
- Gear or synchronizer replacement
- B16/B18 transmission restoration
- Performance transmission assembly
- Replacing a worn mainshaft bearing helps restore proper shaft support and may prevent additional damage to surrounding transmission components.
Installation Notes
- Proper installation is essential for maintaining correct transmission shaft alignment and bearing performance.
- Before installation, inspect the transmission mainshaft, bearing seating surfaces, and transmission housing for wear or damage.
- Confirm that the replacement bearing matches the original component's dimensions and specifications.
- Use appropriate bearing removal and installation equipment to prevent damage to the bearing races, shaft, or transmission housing.
- Important: Angular contact bearings must be installed in the correct orientation and position according to the Honda factory service manual. Improper installation can affect load support and transmission operation.
- Apply installation force only to the appropriate bearing race. Never transmit pressing force through the bearing balls, as this can damage the bearing.
- Inspect related transmission bearings, synchronizers, gears, and shaft components while the gearbox is disassembled.
- Follow the Honda factory service manual for the correct installation procedures, shaft clearances, and transmission reassembly specifications.
- After reassembly, refill the transmission with the manufacturer-specified manual transmission fluid and verify proper operation.
- Note: Includes one genuine Honda OEM Mainshaft Angular Ball Bearing (28x72x18mm). Transmission shafts, gears, synchronizers, seals, and additional bearings are sold separately unless otherwise specified.
For Honda and Acura enthusiasts rebuilding a B-Series manual transmission, restoring an original Civic Si or Integra drivetrain, or preparing a performance gearbox, this genuine Honda OEM Mainshaft Angular Ball Bearing delivers factory-correct dimensions, precise shaft support, and dependable transmission performance.
| Part Number: | 91004-P21-003 |
| Brand: | Honda |
WARNING: This product may contain chemicals known to the State of California to cause cancer or birth defects. www.P65Warnings.ca.gov.
Vehicle Fitment
| Year | Make | Model | Trim |
|---|---|---|---|
| 1992 | Acura | Integra | GS |
| 1992 | Acura | Integra | GS-R |
| 1992 | Acura | Integra | LS |
| 1992 | Acura | Integra | RS |
| 1993 | Acura | Integra | GS |
| 1993 | Acura | Integra | GS-R |
| 1993 | Acura | Integra | LS |
| 1993 | Acura | Integra | RS |
| 1994 | Acura | Integra | GS-R |
| 1994 | Acura | Integra | LS |
| 1994 | Acura | Integra | RS |
| 1994 | Honda | Civic del Sol | VTEC |
| 1995 | Acura | Integra | GS-R |
| 1995 | Acura | Integra | LS |
| 1995 | Acura | Integra | RS |
| 1995 | Acura | Integra | Special Edition |
| 1995 | Honda | Civic del Sol | VTEC |
| 1996 | Acura | Integra | GS-R |
| 1996 | Acura | Integra | LS |
| 1996 | Acura | Integra | RS |
| 1996 | Acura | Integra | Special Edition |
| 1996 | Honda | Civic del Sol | VTEC |
| 1997 | Acura | Integra | GS |
| 1997 | Acura | Integra | GS-R |
| 1997 | Acura | Integra | LS |
| 1997 | Acura | Integra | RS |
| 1997 | Acura | Integra | Type R |
| 1997 | Honda | Civic del Sol | VTEC |
| 1998 | Acura | Integra | GS |
| 1998 | Acura | Integra | GS-R |
| 1998 | Acura | Integra | LS |
| 1998 | Acura | Integra | RS |
| 1998 | Acura | Integra | Type R |
| 1999 | Acura | Integra | GS |
| 1999 | Acura | Integra | GS-R |
| 1999 | Acura | Integra | LS |
| 1999 | Honda | Civic | Si |
| 2000 | Acura | Integra | GS |
| 2000 | Acura | Integra | GS-R |
| 2000 | Acura | Integra | LS |
| 2000 | Acura | Integra | Type R |
| 2000 | Honda | Civic | Si |
| 2001 | Acura | Integra | GS |
| 2001 | Acura | Integra | GS-R |
| 2001 | Acura | Integra | LS |
| 2001 | Acura | Integra | Type R |
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