In the early 80's the US Postal Service was one of the first vehicle fleets to ban use of asbestos brake linings. With the replacement brake parts manufactures, knowing that in short few years the manufacture of asbestos brake was to be ban by law,the Postal became one of the "test beds" for the soon to be required "non-abestos" linings.About the sametime it also took on the use of "DOT 5" brake fluid.Unfortuantely the brake failures & maintenance increased about 75-80%.Every thing from leaks, to loss of pedal. A carrier would call in Saying he had "no brake pedal". By the time the vehicle was towed in and the next day or so we got to check it out, the brakes would be fine.Closer investigation reveal Silicone fluid the culprit, not the originally accused "Non- asbestos" linigs.
It's a "DOUBLE DAMN"--in the case of a Postal carrier or as PHAT said a race car driver's repeated use of the brake was double trouble.Silicone fluid does not absorb water but it does absorb "air"and the brake system being vented the more the pedal was used the more the fluid became "aerated" so the pedal became "spongy" or even went away completely. After the vehicle set for awhile and all the air bubbles disappeared the brakes were fine. The "Double Damn" was that when the air got into the fliud,the tiny bubbles created were very "abrasive"which lead to failure of master & wheel cylinder rubber parts & their bores(especially aluminum M.C.'s).Silicone brake fliud is also affected by altitude and as stated by many brake part manufactures & Chysler Corp. for one: "Warranty Void if DOT 5 fliud is used". "What's" a little"bubbled" paint when DOT 3&4 fliuds are in less question and probably "Safer". Paulweldit
[ April 13, 2002: Message edited by: PAULWELDIT ]</p>