Mopar Action On-line – Tech Questions

Tech Question

John Veatch, Houston, TX, 1956 Dodge Coronet 230

I have used silicone brake fluid since the late 70’s. Infact it was so long ago, they didn’t even require purple dye. I concur witheverything you have stated in the past, I have both filled systems with itand topped off systems. In all cases, I can say my brake system sealing andcorrosion probles virtually vanished. Now to my questions. What is theactual engineering reason ABS systems do not recommend this fluid? I haveheard it is more compressible, but if so, that would defy the laws ofphysics stating liquids are virtually incompressible. If this is thereason, is it due to entrained air? Would pulling a vacuum on the fluidtake care of this? Is this, in fact, a myth and the reason is more liabilityrelated? For years I have wanted someone knowledgeable to shoot straightwith me on this, I turn to you for an honest answer…


I think it has to do with viscosity. In my experience, most DOT5 is a bit’thicker’ than the standard mineral-based crap. This also explains why someguys have bleeding problems, air bubbles take a bit longer to gravitate upand out, and some GM masters have a very small compensating port, causingslow system refill. (Never been a problem on any Mopar).

Correct: Of course, fluids are basically not compressible.

I have also used it for about 35 years, but I don’t use it in the new ABScars. It might be fine, in actuality, I just haven’t tried it.



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