I got to wondering (as I frequently do) about the military's fascination with DOT 5 fluid.

Read through this thread, especially POST #8.

- https://www.steelsoldiers.com/threads/dot-3-or-dot-5-brake-fluid.10484/#

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Re silicon brake fluid.  Many years ago at Ford and involved in a torque converter shudder issue.  One of the team members was a tribologist/fluid specialist.  He was there a long time and involved with the various transmission fluids, among other things.  I asked him why silicone brake fluid wasn't being used as the brake system wouldn't corrode, ... .  He indicated, that it is not hygroscopic and that depending on temperature, water in the system can freeze and could result in brake failure.  Being vehicles are sold to the general public, all factors have to be considered.

Regards,
Dennis

A silicon compatible brake lamp switch is available from HARLEY or a vendor such as RON FRANCIS.

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Just wondering, what about problems (I seem to recall) concerning the orig. type brake light switch when using silicon fluid? Or, was that merely due to whatever rubber compound used at the time?

6 VOLTS/POS. GRD. NW INDIANA

I asked that question of Master Power Brakes Salesman and got a non-answer. He skirted the issue. I asked because they state in their literature that if you use DOT 5, it will void their product warranty on the Power Brake Booster system that they sell

I failed to notice "system" on the first read. I thought that they were not warranting the booster only purchase/install on a DOT 5 system (but I now realize why they wouldn't warranty that scenario also).

The reason(s) for a major brake vendor such as MPB (and they are a class act IMO) limiting their component(s) warranty as to use of DOT 5 is explained in the terms aerobic and compressibility, along with water (vapor - humidity). DOT 3, 4 and 5.1 will absorb and carry the water whereas 5 won't.

One should also consider if a MC leaks fluid into the booster and is drawn into the engine.

If a DOT upgrade is not performed correctly and the system fails (or the system fails due to the fluid), the first thing that will happen is that the vendor will be blamed as to quality of components supplied. Makes perfect sense to me as law suits are very costly.

I just want all sides of the equation to be heard. If you have done the conversion and have had no problems, good. But maybe you also live in a low humidity area and/or have not maxed the brakes out.

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My 55 T-Bird restoration was completed in 1985 with new stainless system using DOT 5. Zero problems.

1955 312 T-Bird Warwick, NY

I have run Dot 5 in my 57 T Bird and 65 Mustang for many years. No issues with either. Did complete rebuild with new lines on both when I did them. 

I have Dot 5 in two cars, one which has been in there for many years.  Absolutely zero problems with it.Fluid in master is always clean.

If doing a complete brake job on a non dot 5 car, I would change it over to Dot 5.

I think the water issue is a canard.  Never heard of anyone who has a water issue with Dot 5.


54 Victoria 312;  48 Ford Conv 302, 56 Bird 312
Forever Ford
Midland Park, NJ

Just so everyone understands DOT 5

DOT 5 doesn’t absorb moisture, so some folks think it is the better choice, but is it?   Before you go rushing off to the parts counter, remember even though DOT 5 doesn’t absorb water, it can’t/won’t prevent moisture from entering the brake system.  And since the water isn’t absorbed by DOT 5, moisture puddles and causes localized corrosion within the brake system.  As funny as it sounds, DOT 3, 4, and 5.1 absorb moisture, which in turn eliminates the puddling that can cause corrosion. More importantly, when brake fluid heats up, water trapped inside the brake lines (but not absorbed by the brake fluid) is converted from liquid to vapor.  Steam compresses easier than liquid.  With this in mind, imagine barreling down the road at high speed and hitting the brakes.  When the hydraulics sends DOT 5 fluid through a pocket of steam in the line, that drop in pressure creates a soft pedal.

DOT 3 and 4 are hygroscopic in that the water vapors are suspended within the fluid. It has to be serviced on a regular basis. DOT 5 is not hygroscopic but water (vapor) still enters the system. It will puddle at the lowest points in the system, ie. MC,wheel cylinders, caliper and any valving. On repeated applications, any water suspended in the fluid may turn to steam and resulting loss of pedal. The brake system components must be compatible. No mixing.

DOT 5 was released for road track cars and is changed frequently as it will aerate

I can understand MPB not warranting hydraulic parts but not a booster. It may be due to a lot of warranty claims resulting from DOT 5 usage.

NOT FOR USE IN ABS SYSTEMS!

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Thank you VERY much Ted for your response to my question on DOT 5 brake fluid  You have put my mind at ease for sure for my most recent system change About 15 years ago I did a complete body off-the-frame restoration of my '57 Thunderbird. At that time that included a complete replacement of all the stock brake system components, i.e. stainless brake lines,drums, shoes master cylinder etc and refill system with DOT 5 fluid. Since then, I have had ZERO  issues with my brake system. The past few years I added a disc brake kit to the front with a kit from a "76 Ford Granada, with a dual master cylinder and a MPB proportioning valve, again with absolutely no problems relative to brake fluid.Thats why I was shocked when the Rep at MPB said IF I put DOT 5 in my system, MPB would void their warranty on their Brake Booster kit that I have installed on my T'bird!  Again , thanks very much for setting me straight on what I have done...Dick Palmer