Brake Fluid Reservoir for Master Cylinder | Specifications & Standards

Product Specifications

Technical details and manufacturing context for Reservoir

Definition

The reservoir is a critical component of the brake master cylinder assembly that holds and supplies brake fluid to the hydraulic braking system. It maintains the proper fluid level to ensure consistent brake pressure and compensates for fluid displacement during brake pad wear and temperature changes. Typically made from polypropylene, nylon, or polyethylene, the reservoir is designed to withstand the operating environment of a motor vehicle. It features separate compartments for the primary and secondary circuits in dual-circuit braking systems, ensuring that a failure in one circuit does not deplete the fluid supply for the other. The reservoir operates under atmospheric pressure, with fluid flowing to the master cylinder chambers through ports. As brake fluid is consumed during braking or leaks occur, the reservoir replenishes the system. Key parameters include a capacity of 0.2–0.5 liters for passenger cars, an operating pressure range of 0.1–0.3 MPa (with a burst pressure of at least 1.5 MPa), and an operating temperature range of -40 to 85°C. The material is often PA66+30GF (polyamide 66 with 30% glass fiber) for strength and heat resistance, and seals are made of EPDM rubber compatible with brake fluid. The reservoir outlet typically uses an M12×1.5 thread, and the assembly weighs between 0.15 and 0.25 kg. It is compatible with DOT 3 and DOT 4 brake fluids, and the maximum allowable leakage rate is ≤0.05 cm³/min. Standards such as ISO 16750-4, ISO 1043, ASTM D2000, ISO 965, and FMVSS 116 are referenced for verification. Always confirm model-specific values and standards with the legal manufacturer or supplier.

Working Principle

The reservoir stores brake fluid under atmospheric pressure and supplies it to the master cylinder chambers through ports. As brake fluid is consumed during braking or leaks occur, the reservoir replenishes the system. It typically has separate compartments for the primary and secondary circuits in dual-circuit braking systems, ensuring that a failure in one circuit does not deplete the fluid supply for the other. The fluid level must be maintained within specified limits to ensure consistent brake pressure and to compensate for fluid displacement due to brake pad wear and temperature changes.

Common Materials

Polypropylene, Nylon, Polyethylene

Technical Parameters

Parameter	Typical range	Notes & selection driver
Capacity	0.2–0.5 L	Typical brake fluid reservoir volume for passenger cars.
Operating Pressure	0.1–0.3 MPa	Pressure range for brake fluid flow; above 0.3 MPa may damage diaphragm.
Burst Pressure	1.5 MPa	Minimum burst pressure to ensure safety.
Operating Temperature	-40–85 °C	Temperature range for continuous operation.ISO 16750-4
Material	PA66+30GF	Polyamide 66 with 30% glass fiber for strength and heat resistance.ISO 1043
Seal Material	EPDM	Ethylene propylene diene monomer rubber compatible with brake fluid.ASTM D2000
Thread Size	M12×1.5 mm	Standard thread for reservoir outlet to master cylinder.ISO 965
Weight	0.15–0.25 kg	Weight range for typical reservoir assembly.
Leakage Rate	≤0.05 cm³/min	Maximum allowable leakage under pressure.
Fluid Compatibility	DOT 3/4	Compatible with DOT 3 and DOT 4 brake fluids.FMVSS 116

Ranges are indicative industry figures for RFQ preparation, not a supplier commitment. Confirm every value and standard with the legal manufacturer before ordering.

Components / BOM

Reservoir Cap Part
Seals the reservoir opening to prevent contamination and fluid evaporation

Material: Plastic with rubber seal
Fluid Level Sensor
Monitors brake fluid level and triggers warning light when low

Material: Plastic with electrical contacts
Mounting Bracket Part
Secures the reservoir to the master cylinder or vehicle body

Material: Steel or plastic
Fluid Compartments
The moulded chambers that actually hold the fluid, split so a leak in one circuit cannot drain the other.

Applied To / Applications

This component is essential for the following industrial systems and equipment:

Brake Master Cylinder

View system integration details

Manufacturers of Reservoir

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Compiled and source-reviewed by the CNFX editorial team. Each manufacturer above links to the page on that company's own website where the product is listed, with the date we checked it. How we source and review · Page last updated 6 September 2026

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Frequently Asked Questions

What is the typical capacity of a brake fluid reservoir?

For passenger cars, the typical capacity is 0.2 to 0.5 liters. Always verify the exact capacity for your specific vehicle model with the manufacturer.

What materials are commonly used for brake fluid reservoirs?

Common materials include polypropylene, nylon, and polyethylene. The material may be PA66+30GF for enhanced strength and heat resistance. Confirm the material grade with the supplier.

What is the operating pressure range for a brake fluid reservoir?

The operating pressure range is 0.1 to 0.3 MPa. Exceeding 0.3 MPa may damage the diaphragm. The burst pressure is at least 1.5 MPa. Verify these values for your application.

Which brake fluids are compatible with the reservoir?

The reservoir is compatible with DOT 3 and DOT 4 brake fluids. Always use the recommended fluid type and check compatibility with the manufacturer.

Data Basis

Editorial classification, named public sources where available, and source-reviewed manufacturer records.

Preliminary Technical Classification

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pressure:	Atmospheric to 1.5 bar
other spec:	Fluid volume capacity: 0.1-2.0 L, Material: Polypropylene or Nylon
temperature:	-40°C to 120°C

Reservoir

Product Specifications

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Reliability & Engineering Risk Analysis

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