Interpretation ID: nht93-7.2

DATE: September 30, 1993 Est.

FROM: Randolph Schwarz

TO: John Messera -- NHTSA

TITLE: None

ATTACHMT: Attached to letter dated 5/5/94 from John Womack to Randolph Schwarz (A42; Std. 116)

TEXT:

I would appreciate your help in getting a few short questions answered regarding DOT 5 silicone brake fluid. I had called the NHTSA Hotline and was advised that, as the Engineer for FMVSS 116, you are currently the appropriate person to contact.

My basic question is that when retrofitting a vehicle with DOT 5 silicone brake fluid, does one have to be concerned with the compatibility of this fluid's seal swelling additives with various elastomers that may be used in past and present brake systems, such as SBR, EP, EPDM, neoprene, etc?.

Would the fact that a DOT 5 brake fluid meets Federal Motor Vehicle Safety Standard 116 insure such elastomer compatibility?

With regard to elastomers, does FMVSS 116 only address SBR compatibility (SBR cup tests)?

If FMVSS 116 only mentions SBR, would it be advisable to add other elastomers to the specification or have an advisory note on the product container regarding elastomer compatibility/incompatibility?

Product information from Dow Corning and Union Carbide differ in FMVSS 116 DOT 5 requirement for maximum viscosity at -40 F (900 cSt vs. 1,500 cSt respectively). What should the correct specification be?

If it would help expedite matters, feel free to write your responses directly on this letter. Thank you for your help, and I look forward to hearing from you shortly.