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Dorman M39566 Brake Master Cylinder
Reliable Brake Master Cylinder for Buick, Cadillac, and Oldsmobile
The Dorman M39566 brake master cylinder is engineered to restore proper brake hydraulics in select Buick, Cadillac, and Oldsmobile models. Designed with durable cast iron and a built-in reservoir, this master cylinder ensures consistent brake fluid delivery for safe stopping performance.
- Constructed from cast iron for strength and durability
- Includes reservoir for brake fluid storage
- Master cylinder bore diameter: 40 mm & 1-1/8 inch
- Four outlets with specific thread sizes for rearward and secondary connections
- Compatible with Buick DeVille, Cadillac Eldorado, Fleetwood, Reatta, Riviera, Seville, and Oldsmobile Toronado
- Part number M39566 for precise replacement
Technical Details and Specifications
This Dorman brake master cylinder features a 40 mm (1-1/8 inch) bore diameter, providing the correct hydraulic pressure for the braking systems in the listed vehicles. The cast iron construction offers resistance to wear and heat, essential for reliable brake performance. The included reservoir allows for proper brake fluid containment and circulation. It has four outlets, with rearward outlet sizes of M11 x 1.5 and M16 x 1.5, and secondary outlet thread diameters of M12 x 1.0 and M16 x 1.5, ensuring compatibility with the brake lines on Buick DeVille, Cadillac Eldorado, and other specified models.
Common Applications and Problem Resolution
- Restores brake pressure in vehicles experiencing spongy or unresponsive brakes
- Replaces leaking or damaged master cylinders causing brake fluid loss
- Addresses brake pedal sinking or failure to maintain pressure
- Solves issues related to inconsistent brake fluid flow in Buick, Cadillac, and Oldsmobile models
- Ensures proper hydraulic function for safe braking performance
Installation Notes and Tips
Installation of the Dorman M39566 brake master cylinder requires proper brake system bleeding to remove air and ensure optimal hydraulic pressure. Mounting hardware is not included, so retain original fasteners or acquire appropriate replacements. Verify thread sizes on brake lines to match the specified outlet dimensions. It is recommended to inspect related brake components during installation for wear or damage.
Quality Assurance and Warranty
Dorman manufactures this brake master cylinder to meet or exceed OEM standards for fit and function. The cast iron material and precise bore diameter contribute to long service life. While mounting hardware is not included, the product is backed by Dorman's quality control processes. Please consult Dorman's warranty policy for specific coverage details.
| Brand | Dorman |
|---|---|
| Part Number | M39566 |
| Master Cylinder Bore Diameter | 40 mm & 1-1/8 in |
| Master Cylinder Material | Cast Iron |
| Mounting Hardware Included | No |
| Number of Outlets | 4 |
| Package Contents | Master Cylinder |
| Rearward Outlet Size | M11 x 1.5; M16 x 1.5 |
| Reservoir Included | Yes |
| Secondary Outlet Thread Diameter | M12 x 1.0; M16 x 1.5 |
| Sensor Included | No |
This part fits 30 vehicles. Search below:
| Year | Make | Model | Position | Notes |
|---|---|---|---|---|
| 1993 | Cadillac | DeVille | N/A | Bore: 28.6 mm and 40 mm; wo/Anti-Lock Brake System (ABS) |
| 1992 | Cadillac | DeVille | N/A | Bore: 28.6 mm and 40 mm; wo/Anti-Lock Brake System (ABS) |
| 1992 | Cadillac | Fleetwood | N/A | Exc. Commercial Chassis; Bore: 28.6 mm and 40 mm; wo/Anti-Lock Brake System (ABS) |
| 1991 | Cadillac | DeVille | N/A | Bore: 28.6 mm and 40 mm; wo/Anti-Lock Brake System (ABS) |
| 1991 | Cadillac | Fleetwood | N/A | Bore: 28.6 mm and 40 mm; wo/Anti-Lock Brake System (ABS) |
| 1990 | Buick | Reatta | N/A | Bore sizes: 28.6 mm and 40 mm |
| 1990 | Buick | Riviera | N/A | Bore sizes: 28.6 mm and 40 mm |
| 1990 | Cadillac | DeVille | N/A | Heavy Duty Brakes; Bore: 28.6 mm and 40 mm |
| 1990 | Cadillac | Eldorado | N/A | Bore sizes: 28.6 mm and 40 mm |
| 1990 | Cadillac | Fleetwood | N/A | Heavy Duty Brakes; Bore: 28.6 mm and 40 mm; wo/Anti-Lock Brake System (ABS) |
| 1990 | Cadillac | Seville | N/A | Bore sizes: 28.6 mm and 40 mm |
| 1990 | Oldsmobile | Toronado | N/A | Bore sizes: 28.6 mm and 40 mm |
| 1989 | Buick | Reatta | N/A | Bore sizes: 28.6 mm and 40 mm |
| 1989 | Buick | Riviera | N/A | Bore sizes: 28.6 mm and 40 mm |
| 1989 | Cadillac | Eldorado | N/A | Bore sizes: 28.6 mm and 40 mm |
| 1989 | Cadillac | Seville | N/A | Bore sizes: 28.6 mm and 40 mm |
| 1989 | Oldsmobile | Toronado | N/A | Bore sizes: 28.6 mm and 40 mm |
| 1988 | Buick | Reatta | N/A | Bore sizes: 28.6 mm and 40 mm |
| 1988 | Buick | Riviera | N/A | Bore sizes: 28.6 mm and 40 mm |
| 1988 | Cadillac | Eldorado | N/A | Bore sizes: 28.6 mm and 40 mm |
| 1988 | Cadillac | Seville | N/A | Bore sizes: 28.6 mm and 40 mm |
| 1988 | Oldsmobile | Toronado | N/A | Bore sizes: 28.6 mm and 40 mm |
| 1987 | Buick | Riviera | N/A | Bore sizes: 28.6 mm and 40 mm |
| 1987 | Cadillac | Eldorado | N/A | Bore sizes: 28.6 mm and 40 mm |
| 1987 | Cadillac | Seville | N/A | Bore sizes: 28.6 mm and 40 mm |
| 1987 | Oldsmobile | Toronado | N/A | Bore sizes: 28.6 mm and 40 mm |
| 1986 | Buick | Riviera | N/A | Bore sizes: 28.6 mm and 40 mm |
| 1986 | Cadillac | Eldorado | N/A | Bore sizes: 28.6 mm and 40 mm |
| 1986 | Cadillac | Seville | N/A | Bore sizes: 28.6 mm and 40 mm |
| 1986 | Oldsmobile | Toronado | N/A | Bore sizes: 28.6 mm and 40 mm |
* Always verify fitment with your vehicle's VIN if unsure. Submodel & trim restrictions may apply.
This part directly replaces or is cross-referenced with the following part numbers:
Cross-reference numbers are provided for identification purposes only. Always confirm fitment before ordering.