ISO 4925:2020

INTERNATIONAL ISO
STANDARD 4925
Third edition
2020-07
Road vehicles — Specification of non-
petroleum-based brake fluids for
hydraulic systems
Véhicules routiers — Spécifications pour liquides de frein à base non
pétrolière pour systèmes hydrauliques
Reference number
©
ISO 2020
© ISO 2020
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ii © ISO 2020 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Materials . 2
5 Specifications . 2
6 Test methods . 4
6.1 Viscosity . 4
6.1.1 General. 4
6.1.2 Repeatability (single analyst) . 4
6.1.3 Reproducibility (multi-laboratory). 4
6.2 Equilibrium reflux boiling point (ERBP) . 5
6.2.1 General. 5
6.2.2 Preparation of apparatus . 5
6.2.3 Test procedure . 5
6.2.4 Repeatability (single analyst) . 5
6.2.5 Reproducibility (multi-laboratory). 5
6.2.6 Wet ERBP test . 6
6.3 pH . 9
6.4 Fluid stability . 9
6.4.1 High-temperature stability . 9
6.4.2 Chemical stability .10
6.5 Corrosion .10
6.5.1 Metal strip characteristics prior to testing .10
6.5.2 Preparation of joints .10
6.5.3 Test procedure .11
6.6 Fluidity and appearance at low temperatures .11
6.6.1 At −40 °C for 144 h .11
6.6.2 At −50 °C for 6 h.11
6.7 Water tolerance .12
6.7.1 At −40 °C for 22 h .12
6.7.2 At 60 °C for 22 h.12
6.8 Compatibility/miscibility with ISO 4926 fluid .12
6.8.1 At −40 °C for 22 h .12
6.8.2 At 60 °C for 22 h.12
6.9 Resistance to oxidation .12
6.10 Effect on rubber .13
6.10.1 Test procedures.13
6.10.2 Repeatability (single analyst) .14
6.10.3 Reproducibility (multi-laboratory).14
6.11 Reserve alkalinity according to ASTM D 1121 .14
Annex A (normative) ISO styrene-butadiene rubber (SBR) brake cups for testing brake fluid .15
Annex B (normative) Corrosion test strips .18
Annex C (informative) Corrosion strip assembly .19
Annex D (normative) Standard ethylene, propylene and diene (EPDM) terpolymer rubber
slabstock .20
Annex E (normative) Triethylene glycol monomethyl ether (TEGME) brake fluid grade .22
Bibliography .25
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
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ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
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on the ISO list of patent declarations received (see www .iso .org/ patents).
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expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/
iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 22, Road vehicles, Subcommittee 33
Chassis systems and components.
This third edition cancels and replaces the second edition (ISO 4925:2005), which has been technically
revised.
The main changes compared to the previous edition are as follows:
— a terms and definitions clause was added (Clause 3);
— an additional class 7 is introduced and added to the already existing classes 3, 4, 5-1 and 6;
— the reserve alkalinity is added upon request out of the automotive industry;
— the intended introducing of a stroking test into a future revision of this document is replaced by the
intended introduction of a wear and noise test currently under development in the SAE and ISO TF
lubrication.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
iv © ISO 2020 – All rights reserved

Introduction
The specifications for fluids given in this document incorporate a range of performance standards in
use throughout the world at the time of publication. To the already existing classes 3, 4, 5-1 and 6 an
additional class 7 is added.
The major use of these fluids is in the hydraulic brake and clutch systems of road vehicles, but they can
also be used in any suitable hydraulic system.
INTERNATIONAL STANDARD ISO 4925:2020(E)
Road vehicles — Specification of non-petroleum-based
brake fluids for hydraulic systems
1 Scope
This document provides the specifications, requirements and test methods, for non-petroleum-based
fluids used in road-vehicle hydraulic brake and clutch systems that are designed for use with such fluids
and equipped with seals, cups or double-lipped type gland seals made of styrene-butadiene rubber
(SBR) and ethylene-propylene elastomer (EPDM).
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 37, Rubber, vulcanized or thermoplastic — Determination of tensile stress-strain properties
ISO 48-2, Rubber, vulcanized or thermoplastic — Determination of hardness (hardness between 10 IRHD
and 100 IRHD)
ISO 812, Rubber, vulcanized or thermoplastic — Determination of low-temperature brittleness
ISO 815 (all parts), Rubber, vulcanized or thermoplastic — Determination of compression set
ISO
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