I am restoring a 1966 "K" Fastback. Dearborn car built August 12th. My proportioning valve for my disc brakes was stored in a zip lock plastic bag with automatic transmission fluid for over 30 years ago. Now that I am retired the restoration is going strong. When I took the proportioning valve apart it was in great shape, but the transmission fluid caused the seals to swell. I ordered a new seal kit but the bumper pad is not available and mine has swollen up beyond it's original size. I have read and tried with no success some of the suggestions on the net for shrinking rubber seals. Are there any options for replacement of the bumper pad ( O-ring, round flat rubber washer). Or any technique for shrinking my bumper pad. I have attached a picture showing how much larger the bumper pad seal is when put on the core. Any help would be greatly appreciated.
I need to caution you about what type of rubber that you ultimately use for your proportioning valve application. You discovered a situation regarding "materials incompatibility" when you observed the rubber swelling of bumper pad, i.e. the rubber was NOT compatible with the ATF. The same situation will occur if you select an incompatible elastomer (rubber) for use with brake fluid. Unless you will be using DOT 5 brake fluid in your restored brake system, you WILL encounter premature failure of the rubber-the question is "when". Brake-related rubber components should be made of Ethylene Propylene (EPDM) IF you use DOT 3 or DOT 4 brake fluids. You can get away with using Hydrogenated Nitrile (HNBR), Ethylene Propylene (EDPM), Fluorocarbon FKM, Perflouroelastomer (FFKM), Atlas (TFE/Propylene) FFKM, and/or Butyl IIR for satisfactory results.
I didn't mean to throw a lot of technical crap at you to confuse you. My point is that I want to possibly save your life (and possibly others) when dealing with brake failure caused by materials incompatibility (brake fluid and rubber used in the system). I believe the bottom line is to use Ethylene Propylene (EDPM) in your system and be SAFE.
The above information was taken directly out of the Parker Hannifin O-Ring Handbook ORD 5700. Parker has been around forever and knows what they are talking about.
I am trying to scare you!
I hope this helps.
Frank
