ISO 7631:1985

Overview

ISO 7631:1985 defines performance tests and acceptance criteria for elastomeric cups and seals used in hydraulic braking systems for road vehicles when a petroleum‑base hydraulic brake fluid is used (service temperature up to 120 °C). It applies to moulded seals (cups or double‑lipped gland seals) up to 60 mm diameter, made from high temperature‑resistant rubber. The standard covers test methods, marking, packaging and inspection requirements - but does not specify rubber chemical composition, tensile strength or elongation.

Key topics and requirements

• Scope and applicability: Wheel and master cylinder cups/seals for petroleum‑base fluids; excludes disc brake seals and O‑rings for drum wheel cylinders.
• Workmanship & identification: Seals must be free from visible defects (blisters, pin‑holes, cracks) and conform to dimensional drawings. Manufacturer identification and the mark “ISO 7631” are to be moulded in; a green identification (ink or tinted elastomer) denotes compatibility with petroleum‑base fluid.
• Hardness range: Product hardness is referenced (between 30 and 85 IRHD).
• Performance tests:
  • Resistance to fluid at elevated temperature (120 °C) - dimensional, volume and hardness changes after immersion in reference fluid.
  • Precipitation test - checks for sediment formation in brake fluid after contact with seals.
  • Heat‑pressure stroking for wheel and master cylinder seals - long‑duration dynamic test evaluating lip diameter change, leakage, corrosion and surface deterioration.
  • Low‑temperature leak and bend tests - verify sealing and flexibility at low temperatures.
  • Oven ageing and storage corrosion - hardness change limits (e.g., oven ageing change typically limited to 0 to +10 IRHD) and checks for corrosion after humidity cycling.
• Sampling and packaging: Lot sizes, test frequency and packaging are to be agreed between supplier and purchaser.

Applications and users

ISO 7631 is essential for:

• Automotive OEMs and brake system designers validating seal performance with petroleum‑base brake fluids.
• Component suppliers and molders producing high‑temperature elastomeric seals.
• Testing laboratories and quality engineers performing acceptance and type tests (dimensional, hardness, stroking, precipitation).
• Regulatory and procurement teams specifying compatibility and durability requirements for hydraulic braking systems.

Using ISO 7631 helps ensure reliable sealing performance, fluid compatibility, and consistent manufacturing quality in automotive hydraulic brakes.

Related standards

• ISO 7308 - dimensions/requirements for petroleum base hydraulic brake fluid (referenced)
• ISO 7309 - petroleum base hydraulic brake fluid (compatibility reference)
• ISO 40 - vulcanized rubber hardness testing
• ASTM references cited in ISO 7631 for ovens and precipitation testing (to be replaced by ISO equivalents where available)

Keywords: ISO 7631, elastomeric cups and seals, hydraulic braking systems, petroleum‑base brake fluid, wheel cylinder seals, master cylinder seals, high temperature rubber, seal testing, heat‑pressure stroking, precipitation test.