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 invite everyones's comments    Dick Palmer

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.

There is a very good reason(s) but it is concerning why the rep would not or could not explain why.

Read Here - https://techtalk.mpbrakes.com/brake-fluid/can-i-use-dot-5

____________________________

Pros and cons of Dot 5 brake fluid

Cons:
Potential for aeration if doing repeated pedal pumping.
More sensitive to air in the system.  Do not use a pressure bleeder to bleed the brakes.
Complaints about a non-firm pedal in some applications.  Air?
System must be cleaned completely of Non Dot 5 fluids before using.
Incompatible with the standard glycol based brake fluids.  Dot 5 is silicone based.
Must be labeled to insure that a non Dot 5 fluid is not put into a system that has Dot 5.
Easily confused with Dot 5.1 which is glycol based.
Some rubber components may not be Dot 5 compatible.
More expensive and harder to find that Dot 3-4 fluids.
Not all stores will have Dot 5 brake fluid available.

Pros:
Not hydroscopic meaning it will not pull atmospheric moisture into the brake system.
No mud forming in the wheel cylinders over the long haul.
Rust in the brake system is minimized.
Less maintenance when rebuilding a system that has been using Dot 5 fluid.
Safe for painted surfaces.
Higher boiling point.
Much longer life span than Dot 3-4 fluids.

With that being said, all my race cars use Dot 5 fluid.  I also have a pair of Vintage cars using it.  My ’55 Customline has had Dot 5 fluid for over 200K miles and zero issues.  I’ve been into the ‘55’s brake system during that time frame for a rebuild and all the wheel cylinders were nice and clean; no mud, no sludge.  The master cylinders on my Dot 5 equipped vehicles all have their fill lids appropriately labeled so that glycol based fluids do not accidentally get used.

Feel free to add additional comments.  Horror stories always welcome.

Lorena, Texas (South of Waco)

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

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!

____________________________

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

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. 

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 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.

____________________________

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