Re: [FWDLK] BRAKE FLUID QUESTION

The brake systems are not hermetically sealed. Water molecules can creep past the rubber wheel cylinder seals and into the master through the vent, or even past the diaphragm [closed system] of the master. Once in the DOT 3, they migrate throughout the system until evenly dispersed. This is why you should flush the old fluid every couple of years, give or take a year depending on the dryness of your climate.

If a DOT 5 system is contaminated with DOT 3, say at a low spot like a wheel cylinder, then all of the moisture gets concentrated in a small amount of DOT 3 and is not diluted and dispersed into the larger system. This can cause local rusting at an accelerated rate. This is why it is important to remove ALL the DOT 3 when installing DOT 5.

One of the better points of the Mopar brakes is that the aluminum wheel cylinder pistons were anodized. This blocks the galvanic action between the disimilar metals (iron and aluminum) and greatly slows the rust process. Other manufacturers didn't anodize their pistons and they rust much faster.

Dave Homstad

56 Dodge D500

On Tue, Aug 30, 2011 at 8:16 PM, Jim Rawa wrote:

i have heard the "claim" of collecting water.... but... lets start with the basics.. silicone is non-hygroscopic, so.... where is the water coming from? atmospheric transfer due to a vented master would yield so little condensation, it would never make it out of the master, let along to the wheel cylinders, in my experience/opinion. with a diaphragm [closed system] master, the advent of moisture attraction is minimized to scavenging while caliper pistons/wheel cyl pistons travel, and when the boots are compromised.

as for not mixing... in an emergency situation... consider the fact you are solely compressing a fluid, to displace it into a different chamber to yield and action... so, even if the mix looks liek a lava lamp, you will be able to stop.

i had an emergency situation dealing with a friend shipping a car, the morning the shipper showed up... he apparently had never checked the master, it leaked its last few drops overnight, and had no pedal when transporters arrived- it was in a bare-bones storage location of mine, where there were no automotive supplies... except for a "decorative" vintage can of marvel mystery oil..... yes, DOT3 and marvel will mingle and allow you to stop, longevity.... not my problem!

-----Original Message-----

From: Bjwt 56 <Bjwt56@xxxxxxx>

To: L-FORWARDLOOK <L-FORWARDLOOK@xxxxxxxxxxxxx>

Sent: Sun, Aug 28, 2011 4:58 pm

Subject: Re: [FWDLK] BRAKE FLUID QUESTION

Guys FYI I have had DOT 5 fluid in my 56 Fury for over a decade with no problems. The Fury has stainless steel lines, brass lined cylinders and regular rubber seals and connecting lines.

John Teske

In a message dated 8/28/2011 8:41:45 P.M. Eastern Daylight Time, whuff@xxxxxxxxxxwrites:

One criticism of silicon fluid that I have heard, but never actually seen documented, is that BECAUSE it will not absorb water, the moisture can collect beneath it and corrode brake cylinders. Not sure it that really makes sense or not.

Bill Huff

At 8/28/201101:32 AM, Dave Homstad wrote:

I am not an expert on brake fluids. I have heard that silicone DOT 5 does not lubricate the rubber/ wheel cylinder wall interface very well, causing wear of the rubber seal. In cars infrequently driven, like most collector cars, this should not be an issue. The non-hygroscopic nature of the fluid is more important. I also have 2 thoughts which could use input:

1. So DOT 5 doesn't mix with 3 or 4. So how is that a problem?

2. For our open vented and unsealed systems, maybe a 1/4 inch layer of DOT 5 floating on top of the regular fluid might slow moisture absorbtion.

Dave Homstad

56 Dodge D500

On Sat, Aug 27, 2011 at 4:16 PM, Bob Jasinski wrote:

DOT 5 fluid (silicone fluid) )is the only brake fluid that is not hygroscopic (not hydroscopic), like DOT 3 and 4 which are hygroscopic, that is, they attract and retain moisture within the molecular content of the fluid. I too, have poured both in a clear jar and sat it on a shelf for months and saw no interaction between the two. I would not recommend mixing it in a car's brake system though. Its best to do a thorough flush and refill, and even better when the system is being rebuilt with new rubber parts installed.

Bob J

1961 300G convert running DOT 5 silicone fluid for 32 years.

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