Interpretation ID: 9211
141 North Madison Drive
South Plainfield, NJ 07080
Dear Mr. Schwarz:
This responds to your letter to Mr. John Messera of NHTSA, requesting an interpretation of Federal Motor Vehicle Safety Standard No. 116; Motor vehicle brake fluids. Your letter has been referred to my office for a response. As a consumer retrofitting your vehicle with DOT 5 brake fluid, you had several questions concerning the possible effects that an ingredient in the brake fluid might have on elastomers used in brake systems. Your questions are answered below.
You mentioned "seal swelling additives" added to DOT 5 brake fluid, that contact various elastomers in the brake system. Your first question was, when brake fluid manufacturers combine additives with brake fluid, should consumers be concerned with the combined fluids' compatibility with various elastomers used in braking systems?
Standard No. 116 defines, at S4. Definitions, brake fluid as a liquid designed for use in a motor vehicle hydraulic brake system where it will contact elastomeric components made of: styrene and butadiene rubber (SBR); ethylene and propylene rubber (EPR); polychlorophene (CR) brake hose inner tube stock; or natural rubber (NR). In order to minimize failures in hydraulic braking systems, Standard No. 116 specifies minimum performance standards for brake fluids. These performance standards include tests for styrene and butadiene rubber cups, the most common type of elastomer in a hydraulic brake system. The brake fluid manufacturer must certify that the brake fluid complies with Standard No. 116. (See S5.2.2(d).) While DOT 5 brake fluid must meet Standard No. 116, the specific ingredients in the fluid are not regulated by the standard.
The brake fluid manufacturer is expected to be aware that in addition to SBR, its brake fluid may contact EPR, CR, and NR elastomers in the brake system. Thus, the brake fluid manufacturers must ensure that contact between the fluid and the above stated elastomers would not result in a safety- related defect under the National Traffic and Motor Vehicle Safety Act. Sections 151-159 of the Safety Act concern the recall and remedy of products with defects related to motor vehicle safety. In the event that the brake fluid manufacturer or NHTSA determines that the brake fluid contains a safety related defect, the brake fluid manufacturer would be responsible for notifying purchasers of the defective brake fluid and remedying the problem free of charge.
Your second question was whether DOT 5 brake fluid's compliance with Standard No. 116 ensures compatibility with elastomers. The answer is yes, for SBR elastomers. Further, besides Standard No. 116, the brake fluid manufacturer is subject to sections 151-159 of the Safety Act, that were previously discussed. At this time, NHTSA is not aware of safety related defects resulting from other ingredients used with brake fluid.
Your third question was whether Standard No. 116 only addresses SBR compatibility with brake fluid. Standard No. 116, at S4, addresses brake fluid that contacts four elastomer types. However, the tests specified in the standard are only of the most commonly used SBR cups.
Your fourth question was, if Standard No. 116 only mentions SBR elastomer, would it be advisable to add other elastomers to the specification, or to discuss elastomer compatibility on the brake fluid container?
Information discussing the elastomer compatibility of the brake fluid, or other ingredients, may be voluntarily placed on brake fluid containers. Standard No. 116 specifies information that brake fluid containers must carry. However, Standard No. 116 does not prohibit manufacturers from noting on brake fluid containers, compatibility of the silicone brake fluid, or other ingredients, with various elastomers.
Finally, you asked what Standard No. 116 specifies as the maximum viscosity for DOT 5 brake fluid, at -40 degrees Fahrenheit. Standard No. 116 specifies, at S5.1.3(c), that the maximum viscosity is 900 centistokes (cSt).
I hope that this information is helpful. If you have any further questions, please contact Dorothy Nakama of my staff at (202) 366-2992.
Sincerely,
John Womack Acting Chief Counsel
ref:116 d:5/5/94