Re: Silicon brake fluid

Posted by jfrom@kanter On 2018/2/13 8:41:13

Kanter Auto Products has been rebuilding Bendix Treadle Vacs for over 50 years and we have diagnosed failures in many units submitted to us by Packardinfo members.. We used to sell Silicone fluid until it became widely available. DOT 3, DOT 4 and DOT 5.1 are polyglycol based and absorb water, DOT 5 IS the only Silicone based brake fluid, DOT 5 and Silicone are just different names for the same thing. DOT 3,4,5 and 5.1 are compatible with each other, they mix without any problems. Mixing Silicone and other brake fluids does not cause a gooey mess/failure, if there were dangers the DOT would require warning labels on all fluids as it would be a safety danger.


The downside to mixing other fluids with Silicone/DOT 5 is the resultant mixture loses the non-water absorbing quality of Silicone/DOT5 thus performs like the newly introduced fluids.


The gasket at the filler opening is either a copper ring or a fiber washer, both are correct, a modern rubber o-ring will do fine as long as it is tested in brake fluid first. There is no pressure at this point, the gasket keeps splashing fluid in and dirt out of the threads.


Leaks at other joints are caused by incorrect installation, being too loose or missing copper washers. At the output distribution block there are two such washers: the larger one goes under the bolt head; smaller goes between the block and the "head nut" on the end of the power brake master cylinder section. Neither of these washers was supplied by Bendix in their kits, neither does the aftermarket. Obviously Bendix knew the the old ones could safely be reused.


A third PLACE IT COULD LEAK IS THE SQUARE CUT RUBBER O RING UNDER the "HEAD NUT" WHICH was supplied by Bendix with their rebuild kits as does the current aftermarket Any one of these missing or loose will cause a leak.


As shown in our long research reported here, failure is due to age, long periods of non-use or incorrect rebuilding.