Dorman M39309 Brake Master Cylinder

Name: Dorman M39309 Brake Master Cylinder
Brand: Dorman
SKU: BKKX-M39309
Price: 106.59 USD
Availability: InStock

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144 vehicles fit this part

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OE Direct Replacement — Bolt-on fit, no modifications needed

Fitment: Chevrolet and GMC, G30, P30, G3500, P3500, C3500, G35, and P35

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Reliable Brake Master Cylinder for Chevrolet and GMC Trucks

The Dorman M39309 brake master cylinder is engineered to restore proper brake hydraulics for Chevrolet and GMC heavy-duty trucks. Designed specifically for models like the Chevrolet C3500 and GMC P3500, this master cylinder ensures consistent brake fluid pressure and reliable stopping power.

Master cylinder bore diameter: 34 mm for precise hydraulic control
Constructed from durable cast iron for long-lasting performance
Includes reservoir for brake fluid, simplifying installation
Two outlets with rearward outlet size of 9/16-18 and secondary outlet thread diameter of 0.5 inches
Package contains the master cylinder only; mounting hardware not included

Technical Details and Compatibility

The Dorman M39309 brake master cylinder is built with a 34 mm bore diameter, providing the correct hydraulic pressure needed for the brake systems on Chevrolet C3500, GMC G30, P30, and P3500 models. Its cast iron construction offers durability and resistance to wear under demanding conditions. The included reservoir allows for proper brake fluid containment, while the two outlets—featuring a rearward outlet size of 9/16-18 and a secondary outlet thread diameter of 0.5 inches—ensure compatibility with the vehicle’s brake lines. This part does not include mounting hardware or sensors, so those components must be sourced separately if needed.

Common Applications and Problem Resolution

Restores brake fluid pressure in Chevrolet C3500 and GMC P3500 brake systems
Replaces worn or leaking master cylinders causing brake pedal sponginess
Addresses brake fluid reservoir leaks or contamination issues
Solves inconsistent braking performance due to master cylinder failure
Prevents brake system failure from internal seal wear or corrosion

Installation Notes and Tips

When installing the Dorman M39309 brake master cylinder, ensure the brake fluid reservoir is properly filled and free of contaminants. Bleed the brake system thoroughly to remove air pockets and verify that the two outlets are securely connected to the brake lines with compatible fittings. Since mounting hardware is not included, retain the original hardware or acquire appropriate replacements. Verify compatibility with Chevrolet C3500, GMC G30, P30, and P3500 models before installation.

Quality Assurance and Warranty

Dorman manufactures the M39309 brake master cylinder to meet or exceed OEM specifications for fit, form, and function. The cast iron construction and precise bore diameter contribute to reliable brake system performance. While specific warranty details are not provided here, Dorman typically offers limited warranties on their brake hydraulics products to ensure customer confidence and product reliability.

Brand	Dorman
Part Number	M39309
Master Cylinder Bore Diameter	34
Master Cylinder Material	Cast Iron
Mounting Hardware Included	No
Number of Outlets	2
Package Contents	Master Cylinder
Rearward Outlet Size	9/16-18
Reservoir Included	Yes
Secondary Outlet Thread Diameter	0.5
Sensor Included	No

This part fits 144 vehicles. Search below:

Year	Make	Model	Body Type	Fuel Type	Position	Notes
1996	Chevrolet	G30		GAS	N/A	w/Dual Rear Wheels (DRW); Bore: 34 mm
1996	Chevrolet	G30		DIESEL	N/A	Brake Master Cylinder with 34 mm bore.
1996	Chevrolet	P30			N/A	Bore: 34 mm; Standard Duty Truck
1996	GMC	G3500		GAS	N/A	w/Dual Rear Wheels (DRW); Bore: 34 mm
1996	GMC	G3500		DIESEL	N/A	Brake Master Cylinder with 34 mm bore.
1996	GMC	P3500	Cab & Chassis		N/A	Brake Master Cylinder with 34 mm bore.
1996	GMC	P3500			N/A	Bore: 34 mm; Standard Duty Truck
1995	Chevrolet	G30		GAS	N/A	w/Dual Rear Wheels (DRW); Bore: 34 mm
1995	Chevrolet	G30		DIESEL	N/A	Brake Master Cylinder with 34 mm bore.
1995	Chevrolet	P30			N/A	Bore: 34 mm; Standard Duty Truck
1995	GMC	G3500		GAS	N/A	w/Dual Rear Wheels (DRW); Bore: 34 mm
1995	GMC	G3500		DIESEL	N/A	Brake Master Cylinder with 34 mm bore.
1995	GMC	P3500	Cab & Chassis		N/A	Brake Master Cylinder with 34 mm bore.
1995	GMC	P3500			N/A	Bore: 34 mm; Standard Duty Truck
1994	Chevrolet	G30		GAS	N/A	w/Dual Rear Wheels (DRW); Bore: 34 mm
1994	Chevrolet	G30		DIESEL	N/A	Brake Master Cylinder with 34 mm bore.
1994	Chevrolet	P30	Cab & Chassis		N/A	9,000 to 14,500 Lb. GVW; Bore: 34 mm; wo/Motorhome Chassis
1994	Chevrolet	P30			N/A	Brake Master Cylinder with 34 mm bore.
1994	GMC	G3500		GAS	N/A	w/Dual Rear Wheels (DRW); Bore: 34 mm
1994	GMC	G3500		DIESEL	N/A	Brake Master Cylinder with 34 mm bore.
1994	GMC	P3500	Standard Cargo Van		N/A	Bore: 34 mm; w/Motorhome Chassis
1994	GMC	P3500	Cab & Chassis		N/A	9,000 to 14,500 Lb. GVW; Bore: 34 mm; wo/Motorhome Chassis
1994	GMC	P3500	Cab & Chassis		N/A	Bore: 34 mm; w/Motorhome Chassis
1994	GMC	P3500			N/A	Bore: 34 mm; wo/Motorhome Chassis
1993	Chevrolet	G30		GAS	N/A	w/Dual Rear Wheels (DRW); Bore: 34 mm
1993	Chevrolet	G30		DIESEL	N/A	Brake Master Cylinder with 34 mm bore.
1993	Chevrolet	P30	Cab & Chassis		N/A	9,000 to 14,500 Lb. GVW; Bore: 34 mm; wo/Motorhome Chassis
1993	Chevrolet	P30			N/A	Brake Master Cylinder with 34 mm bore.
1993	GMC	G3500		GAS	N/A	w/Dual Rear Wheels (DRW); Bore: 34 mm
1993	GMC	G3500		DIESEL	N/A	Brake Master Cylinder with 34 mm bore.
1993	GMC	P3500	Standard Cargo Van		N/A	Bore: 34 mm; w/Motorhome Chassis
1993	GMC	P3500	Cab & Chassis		N/A	9,000 to 14,500 Lb. GVW; Bore: 34 mm; wo/Motorhome Chassis
1993	GMC	P3500	Cab & Chassis		N/A	Bore: 34 mm; w/Motorhome Chassis
1993	GMC	P3500			N/A	Bore: 34 mm; wo/Motorhome Chassis
1992	Chevrolet	G30		GAS	N/A	w/Dual Rear Wheels (DRW); Bore: 34 mm
1992	Chevrolet	G30		DIESEL	N/A	Brake Master Cylinder with 34 mm bore.
1992	Chevrolet	P30			N/A	Bore: 34 mm; w/Motorhome Chassis
1992	Chevrolet	P30			N/A	9,000 to 14,500 Lb. GVW; Bore: 34 mm; wo/Motorhome Chassis
1992	GMC	G3500		GAS	N/A	w/Dual Rear Wheels (DRW); Bore: 34 mm
1992	GMC	G3500		DIESEL	N/A	Brake Master Cylinder with 34 mm bore.
1992	GMC	P3500			N/A	Bore: 34 mm; w/Motorhome Chassis
1992	GMC	P3500			N/A	9,000 to 14,500 Lb. GVW; Bore: 34 mm; wo/Motorhome Chassis
1991	Chevrolet	C3500			N/A	w/Rear Disc Brakes; Stamped-14009146
1991	Chevrolet	G30		GAS	N/A	w/Dual Rear Wheels (DRW); Bore: 34 mm
1991	Chevrolet	G30		DIESEL	N/A	Brake Master Cylinder with 34 mm bore.
1991	Chevrolet	P30			N/A	Bore: 34 mm; w/Motorhome Chassis
1991	Chevrolet	P30			N/A	9,000 to 14,500 Lb. GVW; Bore: 34 mm; wo/Motorhome Chassis
1991	GMC	C3500			N/A	w/Rear Disc Brakes; Stamped-14009146
1991	GMC	G3500		GAS	N/A	w/Dual Rear Wheels (DRW); Bore: 34 mm
1991	GMC	G3500		DIESEL	N/A	Brake Master Cylinder with 34 mm bore.
1991	GMC	P3500			N/A	Bore: 34 mm; w/Motorhome Chassis
1991	GMC	P3500			N/A	9,000 to 14,500 Lb. GVW; Bore: 34 mm; wo/Motorhome Chassis
1990	Chevrolet	G30		GAS	N/A	w/Dual Rear Wheels (DRW); Bore: 34 mm
1990	Chevrolet	G30		DIESEL	N/A	Brake Master Cylinder with 34 mm bore.
1990	Chevrolet	P30			N/A	Bore: 34 mm; w/Motorhome Chassis
1990	Chevrolet	P30			N/A	9,000 to 14,500 Lb. GVW; Bore: 34 mm; wo/Motorhome Chassis
1990	GMC	G3500		GAS	N/A	w/Dual Rear Wheels (DRW); Bore: 34 mm
1990	GMC	G3500		DIESEL	N/A	Brake Master Cylinder with 34 mm bore.
1990	GMC	P3500			N/A	Bore: 34 mm; w/Motorhome Chassis
1990	GMC	P3500			N/A	9,000 to 14,500 Lb. GVW; Bore: 34 mm; wo/Motorhome Chassis
1989	Chevrolet	G30		GAS	N/A	w/Dual Rear Wheels (DRW); Bore: 34 mm
1989	Chevrolet	G30		DIESEL	N/A	Brake Master Cylinder with 34 mm bore.
1989	Chevrolet	P30			N/A	Bore: 34 mm; w/Motorhome Chassis
1989	Chevrolet	P30			N/A	9,000 to 14,500 Lb. GVW; Bore: 34 mm; wo/Motorhome Chassis
1989	GMC	G3500		GAS	N/A	w/Dual Rear Wheels (DRW); Bore: 34 mm
1989	GMC	G3500		DIESEL	N/A	Brake Master Cylinder with 34 mm bore.
1989	GMC	P3500			N/A	Bore: 34 mm; w/Motorhome Chassis
1989	GMC	P3500			N/A	9,000 to 14,500 Lb. GVW; Bore: 34 mm; wo/Motorhome Chassis
1988	Chevrolet	G30		GAS	N/A	w/Dual Rear Wheels (DRW); Bore: 34 mm
1988	Chevrolet	G30		DIESEL	N/A	Brake Master Cylinder with 34 mm bore.
1988	Chevrolet	P30			N/A	Bore: 34 mm; w/Motorhome Chassis
1988	Chevrolet	P30			N/A	9,000 to 14,500 Lb. GVW; Bore: 34 mm; wo/Motorhome Chassis
1988	GMC	G3500		GAS	N/A	w/Dual Rear Wheels (DRW); Bore: 34 mm
1988	GMC	G3500		DIESEL	N/A	Brake Master Cylinder with 34 mm bore.
1988	GMC	P3500			N/A	Bore: 34 mm; w/Motorhome Chassis
1988	GMC	P3500			N/A	9,000 to 14,500 Lb. GVW; Bore: 34 mm; wo/Motorhome Chassis
1987	Chevrolet	G30		GAS	N/A	w/Dual Rear Wheels (DRW); Bore: 34 mm
1987	Chevrolet	G30		DIESEL	N/A	Brake Master Cylinder with 34 mm bore.
1987	Chevrolet	P30			N/A	Bore: 34 mm; w/Motorhome Chassis
1987	Chevrolet	P30			N/A	9,000 to 14,500 Lb. GVW; Bore: 34 mm; wo/Motorhome Chassis
1987	GMC	G3500		GAS	N/A	w/Dual Rear Wheels (DRW); Bore: 34 mm
1987	GMC	G3500		DIESEL	N/A	Brake Master Cylinder with 34 mm bore.
1987	GMC	P3500			N/A	Bore: 34 mm; w/Motorhome Chassis
1987	GMC	P3500			N/A	9,000 to 14,500 Lb. GVW; Bore: 34 mm; wo/Motorhome Chassis
1986	Chevrolet	G30		GAS	N/A	w/Dual Rear Wheels (DRW); Bore: 34 mm
1986	Chevrolet	G30		DIESEL	N/A	Brake Master Cylinder with 34 mm bore.
1986	Chevrolet	P30			N/A	Bore: 34 mm; w/Motorhome Chassis
1986	Chevrolet	P30			N/A	9,000 to 14,500 Lb. GVW; Bore: 34 mm; wo/Motorhome Chassis
1986	GMC	G3500		GAS	N/A	w/Dual Rear Wheels (DRW); Bore: 34 mm
1986	GMC	G3500		DIESEL	N/A	Brake Master Cylinder with 34 mm bore.
1986	GMC	P3500			N/A	Bore: 34 mm; w/Motorhome Chassis
1986	GMC	P3500			N/A	9,000 to 14,500 Lb. GVW; Bore: 34 mm; wo/Motorhome Chassis
1985	Chevrolet	G30		GAS	N/A	w/Dual Rear Wheels (DRW); Bore: 34 mm
1985	Chevrolet	G30		DIESEL	N/A	Brake Master Cylinder with 34 mm bore.
1985	Chevrolet	P30			N/A	Bore: 34 mm; w/Motorhome Chassis
1985	Chevrolet	P30			N/A	9,000 to 14,500 Lb. GVW; Bore: 34 mm; wo/Motorhome Chassis
1985	GMC	G3500		GAS	N/A	w/Dual Rear Wheels (DRW); Bore: 34 mm
1985	GMC	G3500		DIESEL	N/A	Brake Master Cylinder with 34 mm bore.
1985	GMC	P3500			N/A	9,000 to 14,500 Lb. GVW; Bore: 34 mm; wo/Motorhome Chassis
1985	GMC	P3500			N/A	Bore: 34 mm; w/Motorhome Chassis
1984	Chevrolet	G30			N/A	w/Dual Rear Wheels (DRW); Bore: 34 mm
1984	Chevrolet	P30			N/A	Bore: 34 mm; w/Motorhome Chassis
1984	Chevrolet	P30			N/A	Brake Master Cylinder with 34 mm bore.
1984	GMC	G3500			N/A	w/Dual Rear Wheels (DRW); Bore: 34 mm
1984	GMC	P3500			N/A	Bore: 34 mm; w/Motorhome Chassis
1984	GMC	P3500			N/A	Bore: 34 mm; wo/Motorhome Chassis
1983	Chevrolet	G30			N/A	w/Dual Rear Wheels (DRW); Bore: 34 mm
1983	Chevrolet	P30			N/A	Bore: 34 mm; w/Motorhome Chassis
1983	Chevrolet	P30			N/A	Brake Master Cylinder with 34 mm bore.
1983	GMC	G3500			N/A	w/Dual Rear Wheels (DRW); Bore: 34 mm
1983	GMC	P3500			N/A	Bore: 34 mm; w/Motorhome Chassis
1982	Chevrolet	G30			N/A	w/Dual Rear Wheels (DRW); Bore: 34 mm
1982	Chevrolet	P30			N/A	Bore: 34 mm; w/Motorhome Chassis
1982	Chevrolet	P30			N/A	Brake Master Cylinder with 34 mm bore.
1982	GMC	G3500			N/A	w/Dual Rear Wheels (DRW); Bore: 34 mm
1982	GMC	P3500			N/A	Bore: 34 mm; w/Motorhome Chassis
1981	Chevrolet	G30			N/A	w/Dual Rear Wheels (DRW); Bore: 34 mm
1981	Chevrolet	P30			N/A	Bore: 34 mm; w/Motorhome Chassis
1981	Chevrolet	P30			N/A	12,000 to 14,000 Lb. GVW; Bore: 34 mm; wo/Motorhome Chassis
1981	GMC	G3500			N/A	w/Dual Rear Wheels (DRW); Bore: 34 mm
1981	GMC	P3500			N/A	Bore: 34 mm; w/Motorhome Chassis
1981	GMC	P3500			N/A	12,000 to 14,000 Lb. GVW; Bore: 34 mm; wo/Motorhome Chassis
1980	Chevrolet	G30			N/A	w/Bendix Brakes; Bore: 34 mm
1980	Chevrolet	P30			N/A	Bore: 34 mm; w/Motorhome Chassis
1980	Chevrolet	P30			N/A	12,000 to 14,000 Lb. GVW; Bore: 34 mm; wo/Motorhome Chassis
1980	GMC	G3500			N/A	w/Bendix Brakes; Bore: 34 mm
1980	GMC	P3500			N/A	Bore: 34 mm; w/Motorhome Chassis
1980	GMC	P3500			N/A	12,000 to 14,000 Lb. GVW; Bore: 34 mm; wo/Motorhome Chassis
1979	Chevrolet	G30			N/A	w/Bendix Brakes; Bore: 34 mm
1979	Chevrolet	P30			N/A	Bore: 34 mm; w/Motorhome Chassis
1979	Chevrolet	P30			N/A	12,000 to 14,000 Lb. GVW; Bore: 34 mm; wo/Motorhome Chassis
1979	GMC	G3500			N/A	w/Bendix Brakes; Bore: 34 mm
1979	GMC	P3500			N/A	Bore: 34 mm; w/Motorhome Chassis
1979	GMC	P3500			N/A	12,000 to 14,000 Lb. GVW; Bore: 34 mm; wo/Motorhome Chassis
1978	Chevrolet	G30			N/A	Bore: 34 mm; 8,100 to 10,000 Lb. GVW; Compare to Original
1978	Chevrolet	P30			N/A	Bore: 34 mm; w/Motorhome Chassis
1978	Chevrolet	P30			N/A	12,000 to 14,000 Lb. GVW; Bore: 34 mm; wo/Motorhome Chassis
1978	GMC	G35			N/A	Bore: 34 mm; 8,100 to 10,000 Lb. GVW; Compare to Original
1977	Chevrolet	G30			N/A	Bore: 34 mm; 8,100 to 10,000 Lb. GVW; Compare to Original
1977	Chevrolet	P30			N/A	Bore: 34 mm; w/Motorhome Chassis
1977	Chevrolet	P30			N/A	12,000 to 14,000 Lb. GVW; Bore: 34 mm; wo/Motorhome Chassis
1977	GMC	G35			N/A	Bore: 34 mm; 8,100 to 10,000 Lb. GVW; Compare to Original
1976	Chevrolet	G30			N/A	Bore: 34 mm; 8,100 to 10,000 Lb. GVW; Compare to Original
1976	GMC	G35			N/A	Bore: 34 mm; 8,100 to 10,000 Lb. GVW; Compare to Original

* 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:

10-16411032381164113-1668130.6600614009145174-8332539309783-44006F103238M-86006M1641M900359MC103239

Cross-reference numbers are provided for identification purposes only. Always confirm fitment before ordering.