Wrong fluids in the brake system. - PeachParts Mercedes-Benz Forum

ericnguyen · #1 06-09-2003, 11:17 PM

Dear friends:

Auto manuals always emphasize the importance of using the correct fluid in the brake system, which is either DOT 3 or DOT 4. They say that putting any other oils (engine oil, ATF, PS etc...), even just a very tiny contamination will destroy a brake system.

Could someone clarify how such a damage will be done if an incorrect fluid is used in the brake system?

Thanks a lot.

Best regards,

Eric

mike690003 · #2 06-09-2003, 11:35 PM

i'm waiting on an answer also

1991300SEL · #3 06-10-2003, 12:07 AM

An automobiles brake system is a hydraulic system. To quote a verse from a trade school tech manual I have..."A hydraulic system is basically a system that uses a liquid to transmit motion or pressure from one point to another". The brake system uses a confined brake fluid to transfer brake pedal pressure and motion to each of the wheel brake assemblies.

Brake fluid is designed specifically for this hydraulic engagement. The caliper seals are also designed to work with this fluid. Any other fluid would get past the seals. Brake fluid is also designed to withstand boiling up to a given temp. Brakes get hot and the fluid can boil which will cause reduced braking capabilities. Dot 4's boiling point is a little higher than Dot 3's.

Brake fluid is hygroscopic which means it's a water magnet. This is why it's best to flush/bleed the system annually. Some say in the spring after winter's past. In some places there is no winter and spring is a very wet time. Bottom line - flush/bleed brakes when it's dry - lower humidity.

Simply put - motor oil is for engines, gear oil is for manual trannies/differentials, Dexron-III is for auto trannies, power steering fluid is for power steering units, coolant is for cooling systems and brake fluid is for brake systems.

Chemisty.

haasman · #4 06-10-2003, 12:44 AM

Why It Is Recommended You Have Your Brake Fluid Changed Regularly

--------------------------------------------------------------------------------

When you depress your brake pedal a rod connected to the pedal exerts pressure on a piston which forces brake fluid from the brake fluid resevoir into your master brake cylinder. The brake pedal pressure is transmitted and amplified, from the master cylinder, via brake lines to your calipers or wheel cylinders which force grouped pairs of brake pads into contact with either the brake rotors or drums which bring you and your vehicle to a safe stop.

Friction is created when the brake pads or shoes press against the rotors or drums. This friction is what causes your car to stop when you apply the brakes. The heat that builds up in your drums and rotors (in certain cases the surface temperatures of which can exceed 1333 degrees fahrenheit) also causes the brake fluid to heat up. This is why DOT #3 and DOT #4 brake fluids usually have a boiling point which surpasses 401 degrees fahrenheit (the higher the DOT number, the higher the fluid's minimum boiling point, i.e. DOT #3 is 401 deg. F., DOT #4 is 446 deg. F., and DOT #5 is 500 deg. F).

Over time, though, the heat generated from braking causes the chemical composition of the brake fluid to change. Gasses are boiled out of the brake fluid and since these gasses are more compressible than the brake fluid they came from, you will notice a soft or spongy brake pedal feel.

DOT #3 and DOT #4 brake fluids are made from Polyalkylene Glycol Ether which, by nature, has a very strong attraction to water (brake fluid is hygroscopic). Water contaminating brake fluid makes its boiling point drop which causes bubbles to form in the brake fluid (imagine sprinkling water into a frying pan full of hot oil). Bubbles and water are more compressible than brake fluid which makes it more difficult for the master cylinder to compress the brake fluid and in turn, compress the calipers and brake drums. A sign of this may be a low, soft, or spongy brake pedal feel (caused by the the contaminating bubbles and water compressing before the brake fluid does).

DOT #5 brake fluid, on the other hand, is formulated from silicone. While silicone is not hygroscopic and has a higher boiling point than DOT#3 and DOT #4 brake fluid, any water that gets into the brake system will sink to the lowest point of that system (water being heavier than silicone) and may potentially find its way to the calipers, boil at 212 degrees fahrenheit and cause a vapor lock which could cause brake failure. Additionally, DOT #5 brake fluid, being a synthetic, is much more expensive than DOT #3 and DOT #4 fluids, hence Tire Kingdom uses DOT #5 brake fluid only at the request of the customer.

Water is bad for your brakes. " As little as 3% moisture contamination can reduce the boiling point of brake fluid by as much as 25%. By the time a new car is only 12 months old, it's brake fluid contains about 2% water. After 18 months, the water content is approaching 3%. After several years of service it is not uncommon to find brake fluid containing 7 to 8 % water.

This can lead to a condition called 'fluid boil'. In this condition the driver runs out of pedal stroke without actuating the brakes. Brake heat boils the fluid into vapor so that the pedal stroke is used up to compress gas. With a sufficient vapor accumulation, the master cylinder can run out of stroke before the brakes are applied. Often this condition disappears before being checked, since the vapor converts back to a fluid when it cools."

Water in the brake system can also cause internal corrosion (rusting) of the metal and deterioration of the rubber parts of the brake system from the master cylinder through the brake lines and seals down to the wheel cylinders and caliper pistons. Replacing these parts can be an expensive proposition, especially if the vehicle is equipped with ABS (anti-lock brakes).

How does water get into the brake system? Moisture enters through microscopic pores in the rubber brake hoses and seals, cracks in the rubber brake hoses, leaks in the brake lines, and when the brake fluid resevoir is opened (it does not take much for brake fluid to absorb moisture, especially in a place like Florida where there tends to be a great deal of humidity in the air).

How can you tell when your brake fluid is dirty or contaminated? The color of the brake fluid itself, offers a clue. New, clean brake fluid usually has a golden color (unless it is DOT #5 which may be purple or yellow), while dirty old brake fluid is brown or if heavily contaminated, black. A brake fluid moisture tester can also be used to gauge the purity of the fluid in your brake system.

Most major vehicle manufacturers recommend having your brake fluid replaced about every 2 years (more often in severe driving conditions). Draining and replacing your brake fluid helps to remove contaminants (such as water and rust) and to lubricate the metal and rubber parts of your brake system (like the master cylinder, brake lines and seals, valves, wheel cylinders and caliper pistons) which may help them last longer.

Brake fluid is a technically sophisticated and usage specific chemical. No other fluid can perform the functions it is designed for:

*Brake fluid must not boil under high temperatures.

*Brake fluid must retain its viscosity at temperatures at or below freezing.

*Brake fluid must not readily compress.

*Brake fluid must flow freely through small gauge orifices.

*Brake fluid must not corrode or react with materials in the brake system.

*Brake fluid must be able to lubricate the moving, metallic, and rubber parts of the brake system.

*Brake fluid must remain chemically stable for extended periods of time.

*Brake fluid must be miscible (mixable or compatible) with other glycol based products.

*Brake fluid must not decompose or form gum or sludge in the brake system.

Source: ABCs of Brake Fluid

What affects other fluids (aside from water) would on your braking system vary depending on the fluid. If you ever have the chance, take a small drop of brake fluid and rub it between your thumb and finger. It tends to be quite "grippy" for lack of a better word. Do the same with a drop of oil and it is slippery.

If the wrong "fluid" has been introduced to a braking system, first

>>> >> > DO NOT USE THE BRAKES < << <<<

then use a turkey baster or some method to get as much out of the brake reservoir as possible. Best to remove the maste cylinder reservoir and replace it. Again this all depends on what kind of fluid. Worst case, if something other than brake fluid has been introduced to the system, it may mean a total flushing and/or replacement of all the lines and components.

Haasman

xp190 · #5 06-10-2003, 01:01 AM

great article hassman

or did you copy and paste it?

xp

haasman · #6 06-10-2003, 01:22 AM

I found it on the net, see the link: ABCs of Brake Fluid. Good stuff.

Haasman

Duke2.6 · #7 06-10-2003, 02:18 AM

The first hyraulic systems - automotive brake systems - were produced about 1920. At the time there were no synthetic rubber compounds that were immune to attack from petroleum-based products, so a non-petroleum fluid had to be used. The choice was glycol.

Synthetic rubbers were developed during the WW II era that could resist petroleum-based products. They were first used on hydraulic control systems for aircraft, and hydraulic systems using petroleum-based fluids soon replaced the cables and pulleys on construction and other heavy equipment.

Because automotive brake systems originally used glycol-based fluids, the various authorities ultimately including the US government decreed that automotive brake systems continue with glycol-based fluids because of the logistics issues of having to maintain two different and incompatible fluids in the field and the potential safety issue of mixing petroleum based fluids in older systems that could cause brake failure.

Thus we are stuck with the legacy of glycol-based brake fluid and its moisture absorbtion, which will corrode the internals of the brake system if it is not periodically flushed to purge absorbed moisture. The only other fluid that is acceptable for brake systems is silicone-based, but since it has certain incompatibilites with glycol-based fluids such as miscibility, it is not recommended that the two fluids be mixed, so silicone fluid should only be used in a brake system if the system is completely disassembled and cleaned and then everthing put together with silicone fluid.

Duke

ericnguyen · #8 06-10-2003, 08:32 PM

Dear friends:

Thanks a lot for all your precious information. So we can basically say that all other fluids (except brake fluid) cannot be used in a brake system because of the following main reasons (which other fluids do not have):

1) brake fluid is very incompressible (for braking purpose)
2) brake fluid has high boiling point (for safety purpose)
3) brake fluid has very low freezing point (for very cold environments)
4) brake fluid is not corrosive with brake seals (for longevity purpose)

Eric

Kestas · #9 06-10-2003, 10:34 PM

Other fluids can swell the seals. There is a serious compatibility issue with matching the seal compound to the parent fluid.

Duke2.6 · #10 06-10-2003, 10:35 PM

Quote:

[i]

1) brake fluid is very incompressible (for braking purpose)
2) brake fluid has high boiling point (for safety purpose)
3) brake fluid has very low freezing point (for very cold environments)
4) brake fluid is not corrosive with brake seals (for longevity purpose)

Eric [/B]

1) From a practical standpoint all liquids are essentially incompressible

2) yes 450-500 dry, but only 250-300 wet (when a significant amount of moisture is absorbed)

3) yes

4) glycol based brake fluid will not attack the rubber seals, but the absorbed moisture can corrode the system in addition to lowering the boiling point. This is why conventional glycol base DOT 3 & 4 brake fluid should be periodically replaced.

Duke

csnow · #11 06-10-2003, 11:54 PM

I believe the original question was not about brake fluid types, but about contamination from petroleum products. Accidental contamination, one would presume...

I have read that the rubber parts will react badly to petroleum contamination, even when small amounts are involved (as you say). The dissolved petroleum is said to breakdown the seals. Not sure if it changes swelling characteristics, or literally decomposes the rubber, but it is a bad bad thing... Glycol brake fluid will dissolve oils. It is actually a pretty good solvent. Test it sometime! (Just keep it away from paint). It probably would not have a direct and immediate effect on your braking. The boiling point of oils is also very high.

If you accidentally poured oil in the reservoir, I would immediately get as much of it out as possible with a baster, then flush the system with fresh fluid multiple times. Being a good oil solvent, the fluid should work to flush the oil out quite well. Perhaps with no measurable seal damage... but no promises.

With great embarassment, I will confess:

I actually did the opposite once, and poured brake fluid into a hydraulic OIL reservoir. Really bad idea! (Hey, it was gray market, and all the labels were in German, and I was like 19 then, and what an idiot). Got as much out as possible without resorting to a total disassemble to drain, but every component in the hydraulic system failed within a few months. Brake booster, steering rack, hydraulic pump... Big and very costly mistake! Doh!

Kestas · #12 06-11-2003, 08:53 AM

I'm embarrassed to say I have first-hand experience what contamination can do in brake fluid. 20 years ago I did a complete brake job on my 74 Torino. Instead of brake fluid I flushed the system with mineral spirits. I drove the car 20 miles before the car started going slower and slower and the brakes pretty much locked up. The rotors overheated with a blue temper color on the surface. I had the car towed home where I replaced the master cylinder and the brake seals on all four corners of the car.

Petroleum-based fluids are incompatible with the compound used to make brake seals. The seals will swell if it sees the wrong fluid.

The reason this happened is because I decided to put mineral spirits in an empty brake fluid container. I liked the container. Because of this incident, to this day I make sure everything is properly labeled on my shelf - garage and home.

jsmith · #13 06-11-2003, 12:27 PM

with the older dot 3 fluids you can have some degradation of rubber components (why you get dark fluid). dot 4 addresses this. i use castrol and it says meets dot 3 and 4 specs...

manny · #14 06-11-2003, 12:36 PM

Just one little footnote on this topic.
Do not open/reseal and store brakefluid.
But you probably knew that already.

csnow · #15 06-11-2003, 03:00 PM

Yeah, usually better to buy the small containers unless you are facing multiple vehicles.
Less waste.
Hate sending brake fluid that was never actually used to hazardous waste collection. Just feels wrong.

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