John -
The way I understand it, moisture gets trapped in the brake lines. Having a brake fluid that absorbs moisture is a good thing, since otherwise it has no place to go and settles either between the fluid and the inner line, or by the line-to-wheel cylinder connection, which will cause rust to form. Since DOT 5 does not absorb moisture, that may lead to the condition just described. DOT 3/4 starts out as a golden color, but turns darker as it reaches a moisture saturation level. So I would change out DOT 3/4 every five years or so and your brakes will be happy. Having a soft pedal, IMHO, is a worse alternative to this. Very scary.
There is also something called DOT 5.1, which I haven't researched. Anyone want to chime in ?
Ron
From: Chrysler300@xxxxxxxxxxxxxxx [mailto:Chrysler300@xxxxxxxxxxxxxxx] On Behalf Of John Grady jkg@xxxxxxxxxxxxxxxxx [Chrysler300]
Sent: Tuesday, March 24, 2020 10:02 AM
To: nick@xxxxxxxx
Cc: Mister Michael; Chrysler 300 List
Subject: Re: [Chrysler300] Brake Fluid for a 300F
FYI — Soft pedal with silicone is because you got air entrained in it . Takes months to get out , If ever , if in a car . Must pour very carefully from undisturbed container sitting on a shelf , still for a year , imho. And extremely smoothly , slowly ideally down a paper ramp into master . Anything to avoid aerating it . Just dumping it in makes tiny bubbles . Micro bubbles stay suspended. Soft pedal. I would avoid pressure bleeders . Obviously if you shake can once you are done for .
It is standard in military ( where I got mine surplus —some large cans on eBay ) . Rubber loves silicone , —silicone seals rubber and preserves it twenty years or more . Critically, it does not absorb water .I really believe “sealed for life” .. like a stored military truck. But if you do not know about the easy aeration it will not work .
All glycol absorbs water ; on our cars it ends up over many years in the bottom of wheel cylinders and makes a rust pit as it is heavier than glycol... One day you get a very big sudden surprise .
On several of my cars I added a micro switch to pedal mount to get rid of problematic and in the way hydraulic switches. See 70’s dodge trucks for idea /switch , or make bracket yourself for a real 15 amp large body micro switch . Pedal up holds it open. Helps with dual master room and plumbing too . Although not absolutely sure on any given pressure switch, silicone is more chemically innocuous than glycol (?) so switch failure is most likely due to lousy switch — not silicone ,— plus, and a biggy , a spilled or sprayed drop of glycol , and your paint is absolutely trashed due to the chemical aggressiveness. A leaking master gasket took all the paint off my firewall , under master .
MBenz requires new brake glycol fluid every two years . I did not do that, result was $ 2000 in bills as rubber in ABS system valves fell apart and seals in rear axle disc brakes too, brakes failed after 5-6 years. ... .....personally I think due to crappy German rubber , but it happened .
Temp differences in glycol DOT rankings mean little on drum brakes , but critical on discs . Might as well use best , however.
I would not use the stuff on a rebuild. I have seen those pits on 4- 5 300F, enough for me -/ — and once had the sudden brake failure they imply . As shoes wear , or are replaced , seal moves to new place in wheel cylinder can uncover pit, your brake fluid squirts right out around seal lip .
Just info , your mileage may vary . Most of above info learned the hard way ...... If you go glycol , change it every few years .. keep record..
Ps , glycol probably ok in a car driven a lot , gets warm under hood frequently water vapor probably leaves due to higher vapor pressure etc . But a sitting car must soak it up .. military does not have “ soft pedal ”
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Do not use synthetic if you’re still using the original brake light switch. Supposedly it will cause it to leak and fail. I just use regular brake fluid.
Ready to fill up the master cylinder after replacing all lines. Which brake fluid is most recommended for our cars? Used silcone in other classic cars and have had soft pedal. Tempted to use the original dot 3? Never had a problem with the stuff.
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