Brake fluid is a hydraulic fluid used in vehicle braking systems to transfer force and amplify braking pressure. There are two main types: petroleum-based and non-petroleum. Glycol-based fluids like DOT 3, DOT 4, and DOT 5.1 are most common. DOT 3 has advantages like absorbing less moisture and maintaining a higher boiling point longer. Brake fluid must be changed every two years to prevent moisture absorption from decreasing its boiling point and compromising the braking system.

1. Brake fluid
By PRANAV RAM , B.E Mechanical Engg.

2. What is brake oil and why we use it?
 It is meaning less to have a car without a brake.
 For the vehicles using hydraulic brake system,it is necessary to use Brake
fluid.
 In hydraulic braking ,the fluid required to push the pistons in both main
and wheel cylinders are nothing but brake fluids.
 Lets see about it ……

3. What is brake fluid ?..
 Brake fluid is a type of hydraulic fluid used in hydraulic brake applications
in automobiles, motorcycles, light trucks, and some bicycles.
 It is used to transfer force into pressure, and to amplify braking force. It works
because liquids are not appreciably compressible — in their natural state

4. Brake fluid types
 Generally,there are TWO types of fluid ,they are
 Petroleum based(mineral oil)
 Non-petroleum
 99.9% of vehicle is run with non-petroleum based brake oil.
 It is further classified into
 silicone based
 glycol based
Glycol based brake oil like DOT 3, DOT 4 ,DOT 5.1 etc.. are preferred

5. Characteristics of DOT fluids
Boiling point
The Brake must posses high boiling point,since it must evaporate when
under going high temperature change..
BRAKE FLUID
MINIMUM BOILING POINT (ERBP)
SPECIFICATION
DRY WET
DOT 3 205 Deg C 140 Deg C
DOT 4 230 Deg C 155 Deg C
DOT 5 260 Deg C 180 Deg C

6. Kinematic viscosity:
 All brake fluids (DOT 3, DOT 4, DOT 5 & DOT 5.1) must meet a minimum viscosity
test of not less than 1.5 centistokes at 100° C and must not be more than the
following to meet their various classifications.

7.  It must posses :
Low compressibility
Constant Viscosity
High temperature Stability

8. DOT 3 oil
 Department of transportation 3 (DOT 3) brake oil is preferred by our team,
since it has more advantages from the other types.
 Its dry boiling point (ERBP) is 205°C minimum and wet boiling point (Wet
ERBP) is 140°C minimum.
 It absorbs 1 to 2 percent of water per year depending on climate and
operating conditions. It is used in most domestic cars and light trucks in
normal driving.
 This brake fluid does not require cleaning the system and can be mixed with
DOT 4 and DOT 5.1 without damage the system.

9. Reason for preferring DOT3 than DOT4
 DOT 3 oil absorbs less moisture from the air,than compared to DOT 4 oil
 More over during usage,due to absorption of water from moisture it can
drastically reduce the boiling point of the brake oil.
 here, after period of 2 years,the DOT 4 oil consumes lot of water and leads
to a sharp drop in boiling point that may cause to vapourise.

10. Do we need to change fluid?
 Yes off course, we need to change the brake fluid once in 2 years .
 Or else , it would cause brake failure
 The reason is that the oil absorbs water from moisture and it
decreases the boiling point automatically ,tends to vapourise

11. Percentage of water content
Brake oil must be changed when it reaches its WET BOILING
point

13. Use of DOT 5
 Even though DOT 5 type brake oil doesn’t absorb water, it is not
widely used due to its cost
 IT is used in some old classical cars and bikes like Davidson to avoid
paint work and plastic damage.

14. General drawbacks

15. Corroded materials

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