When and how to bleed brakes on a motor vehicle or Motorcycle

 

Old brake fluid can and will cause sponginess in the system, loss of brakes and internal corrosion.

 

Brake fluid ages and also being most of them are in the Glycol family and what we call “Hygroscopic” which means they absorb water.

 

Over the years, water is drawn in through not just the master cylinder but also through the vehicles rubber hoses which (believe it or not) are to some degrees POROUS.

 

It has been known for a vehicle to have up to 13% water in a Glycol Fluid.

 

There are several brake fluids on the market with various levels of pureness and water content. This always reflects in a boiling point figure as the fluid with more water boils more easily. Fluids with high water content, above 2-3% will cause fluid vapour lock and can cause corrosion within the braking system and ruin the entire brake system causing brake failure.

 

Basically the rule of thumb is to replace the brake fluid by flushing out the old fluid every three years or when the fluid water content rises above 3%.

 

After flushing the old fluid out it will be necessary to BLEED to system to remove all air and this can be easily done with the assistance of a brake bleeder tool which is an inexpensive DIY system.

 

What fluid to buy

Look for a Brake fluid from a small volume SEALED CAN and never use brake fluid from a gallon drum as this will have already deteriorated by 3-5% water content and may even be worse than the fluid you are removing. It may LOOK nice and clean and gold colour like a nice cider but the water content which you cannot see may be high. Once a can is opening in a matter of weeks, it degrades to a lower level of specification. That is why EBC only sell SMAL 250 ml bottles of fluid, use one or two for your car.

 

EBC best brake fluid is known as BF307 Glycol which has a 307 degree boiling point (very high) with less than 0.3 % water content or less expensive EBC Fluids are:

 

EBC DOT-4 Glycol (less than 0.6% water content) or
EBC DOT-3 Glycol (about 1.0% water content).

 

Hints

  • Glycol fluids are corrosive to paints, protect bodywork carefully when bleeding brakes or replacing fluid.
  • Top off fluid reservoir when flushing brakes regularly to avoid drawing air into system.
  • Do not contaminate pads or brake shows with brake fluids and if they do become contaminates change them. Do not touch pads, discs or rotors with fingers that are contaminated with brake fluid.