Overview
ISO 4928:2006 defines performance test requirements for elastomeric cups and seals used in hydraulic braking systems of road vehicles when operated with a non‑petroleum base hydraulic brake fluid (service temperature up to 120 °C). The standard applies to moulded cups or double‑lipped gland seals up to 60 mm diameter made from high temperature‑resistant rubber. It specifies test methods and acceptance criteria but does not set requirements for chemical composition, tensile strength or elongation. Disc brake seals are excluded.
Key topics and technical requirements
- Scope and exclusions: Applies to wheel‑ and master‑cylinder seals (≤ 60 mm); excludes disc brake seals and compound chemical composition requirements.
- General requirements: Workmanship, marking (manufacturer ID and optional “ISO 4928”), packaging and sampling procedures.
- Core performance tests:
- Resistance to fluid at elevated temperature (120 °C) - dimensional change, volume and hardness limits.
- Precipitation (sediment) limits after fluid exposure.
- Heat pressure stroking for wheel cylinder and master cylinder seals - lip diameter retention, leakage criteria, corrosion inspection, hardness change limits and surface condition (no excessive scoring, scuffing, blistering).
- Low‑temperature performance - leakage and bend test (no cracking; shape recovery).
- Oven ageing - hardness change limits and visual condition.
- Corrosion and storage corrosion tests - permissible corrosion mass changes and no jellying or excessive sediment in fluid‑water mixtures.
- Test procedures & references: Dimensional, hardness and ageing test methods reference other ISO documents (e.g., ISO 48 for hardness, ISO 188 for oven ageing, ISO 4926 for reference fluids).
Applications and who uses it
ISO 4928 is used for:
- Automotive OEMs and braking system designers for seal validation and component acceptance.
- Brake system suppliers and elastomer manufacturers for product development, compound selection and quality control.
- Testing laboratories performing certification, endurance and compatibility testing of seals with non‑petroleum brake fluids.
- Procurement and aftermarket buyers who require traceable performance criteria in supplier specifications.
Benefits include improved reliability of brake actuators, reduced risk of fluid contamination or seal failure, and harmonized test criteria for global supply chains.
Related standards
- ISO 4925 - Specification of non‑petroleum‑base brake fluids (fluid compatibility).
- ISO 4926 - Non‑petroleum base reference fluids.
- ISO 48 - Rubber hardness determination.
- ISO 188 - Accelerated ageing and heat resistance tests.
- ISO 1250 - Mineral solvents (referenced for cleaning/solvent use).
Keywords: ISO 4928, brake seals, elastomeric cups, hydraulic braking systems, non‑petroleum brake fluid, high temperature rubber seals, performance tests, wheel cylinder seals, master cylinder seals.