Re: Brakes lights staying on
Posted: Tue Mar 03, 2015 12:52 pm
All true.woodypup59 wrote: Fluids - especially fuels and oils - will swell rubber and plastic materials to some extent, sometimes causing complete liquefaction.
The original BMC components will have been designed to cope with the fluids of the era.
All the changes to modern brake fluids, bio fuels and antifreezes mean that 1950s spec rubber are not suitable anymore.
It is my understanding that up until the mid-1970s the seals used in Lockheed brake systems were formulated from a blend including natural rubber which dictated the exclusive use of DOT-4. I was informed that later brake rubber compounds (mid-1970s and later) have been largely EPDM which is compatible with all common brake fluids.
DOT-5 being a silicone fluid is compatible with EPDM and natural rubber but not compatible with silicone rubber (like RTV). Perhaps the hydraulic brake switches have silicone seals. Regardless, there is a wealth of anecdotal evidence that says you can expect switch failure if your car uses DOT-5.