When to Replace Brake Fluid?
#21
02-12-2009, 07:37 PM
I guess you never change brake pads either? 
Brake fluid most certainly does degrade.
I suppose you think fork oil doesn't need to be replaced either?
All I can say from my personal experience is at least when the brake pads have to be replaced it just makes since to flush the old, black, worn out oil while you have the system open.
Brake fluid most certainly does degrade.
I suppose you think fork oil doesn't need to be replaced either?
All I can say from my personal experience is at least when the brake pads have to be replaced it just makes since to flush the old, black, worn out oil while you have the system open.
Yes, I do replace brake pads, replaced the rears at 25,000 miles, just checked the fronts, about half worn at 30,000 miles. But, you dont have to open up the system to replace pads, so I will leave it alone. Using your rational to change when the pads wear out, I still have about another 30k to go
As far as the one about using a turkey baster to pull the fluid out of the master cyl, what about all the fluid in the lines?
Each to their own...last bike had 65,000 miles on it when traded, and still had the original fluid and the brakes worked fine.
#22
02-13-2009, 05:10 AM
Road Warrior
#23
02-13-2009, 05:43 AM
HDF Community Team
First, when the pads wear, by design the pistons remain in an extended position. Therefore, if you check fluid, it's naturally going to look low due to the fact of the additional fluid needed to occupy the additional space in the calipers. Topping off a master cylinder at that time will make them overfull when the pistons are pushed back during a brake pad replacement and/or tire change.
These master cylinders have a diaphram under the cap which allows for venting the necessary amount of fluid to remain in the system (lines and calipers) without allowing air and consequently moisture to contaminate the fluid. Therefore, assuming the system was properly filled at the factory and unless the system is opened for replacement/repair of the piston, lines or master cylinder, you should never need to add or change fluid.
#24
02-13-2009, 11:00 AM
Automotive brake fluid has many responsibilities. Corrosion protection and lubrication of brake system components are only a portion of the role brake fluid must play.
All automobiles that have a hydraulic braking system must use brake fluid in order for the brake system to operate. The type of fluid used can depend on the type of vehicle and the demands of the vehicles brake system.
The two most common brake fluids used in the automotive industry are fluids that contain Polyalkylene Glycol Ether and fluid that contains Silicone or Silicium-based Polymer. Both Fluids are common but very different in regards to the manner in which they perform. Fluids containing Polyalklene Glycol Ether are more widely used and are the only fluids that should be used in racing brake systems.
Because brake systems may reach extreme temperatures brake fluid must have the ability to withstand these temperatures and not degrade rapidly.
SILICONE BASED FLUID
Fluids containing Silicone are generally used in military type vehicles and because Silicone based fluids will not damage painted surfaces they are also somewhat common in show cars.
Silicone-based fluids are regarded as DOT 5 fluids. They are highly compressible and can give the driver a feeling of a spongy pedal. The higher the brake system temperature the more the compressibility of the fluid and this increases the feeling of a spongy pedal.
Silicone based fluids are non-hydroscopic meaning that they will not absorb or mix with water. When water is present in the brake system it will create a water/fluid/water/fluid situation. Because water boils at approximately 212º F, the ability of the brake system to operate correctly decreases, and the steam created from boiling water adds air to the system. It is important to remember that water may be present in any brake system. Therefore silicone brake fluid lacks the ability to deal with moisture and will dramatically decrease a brake systems performance.
POLYGLYCOL ETHER BASED FLUIDS
Fluids containing Poly glycol ethers are regarded as DOT 3, 4, and DOT 5.1. These type fluids are hydroscopic meaning they have an ability to mix with water and still perform adequately. However, water will drastically reduce the boiling point of fluid. In a passenger car this is not an issue. In a racecar it is a major issue because as the boiling point decreases the performance ability of the fluid also decreases.
Poly glycol type fluids are 2 times less compressible than silicone type fluids, even when heated. Less compressibility of brake fluid will increase pedal feel. Changing fluid on a regular basis will greatly increase the performance of the brake system.
FLUID SPECIFICATIONS All brake fluids must meet federal standard #116. Under this standard is three Department of Transportation (DOT) minimal specifications for brake fluid. They are DOT 3, DOT 4, and DOT 5.1 (for fluids based with Polyalkylene Glycol Ether) and DOT 5 (for Silicone based fluids).
FWIW, My bike takes DOT4 and after 2 years the fluid turns greenish brown in the front caliper from water intrusion and the lever feel gets spongy. Once flushed it is back to normal.
All automobiles that have a hydraulic braking system must use brake fluid in order for the brake system to operate. The type of fluid used can depend on the type of vehicle and the demands of the vehicles brake system.
The two most common brake fluids used in the automotive industry are fluids that contain Polyalkylene Glycol Ether and fluid that contains Silicone or Silicium-based Polymer. Both Fluids are common but very different in regards to the manner in which they perform. Fluids containing Polyalklene Glycol Ether are more widely used and are the only fluids that should be used in racing brake systems.
Because brake systems may reach extreme temperatures brake fluid must have the ability to withstand these temperatures and not degrade rapidly.
SILICONE BASED FLUID
Fluids containing Silicone are generally used in military type vehicles and because Silicone based fluids will not damage painted surfaces they are also somewhat common in show cars.
Silicone-based fluids are regarded as DOT 5 fluids. They are highly compressible and can give the driver a feeling of a spongy pedal. The higher the brake system temperature the more the compressibility of the fluid and this increases the feeling of a spongy pedal.
Silicone based fluids are non-hydroscopic meaning that they will not absorb or mix with water. When water is present in the brake system it will create a water/fluid/water/fluid situation. Because water boils at approximately 212º F, the ability of the brake system to operate correctly decreases, and the steam created from boiling water adds air to the system. It is important to remember that water may be present in any brake system. Therefore silicone brake fluid lacks the ability to deal with moisture and will dramatically decrease a brake systems performance.
POLYGLYCOL ETHER BASED FLUIDS
Fluids containing Poly glycol ethers are regarded as DOT 3, 4, and DOT 5.1. These type fluids are hydroscopic meaning they have an ability to mix with water and still perform adequately. However, water will drastically reduce the boiling point of fluid. In a passenger car this is not an issue. In a racecar it is a major issue because as the boiling point decreases the performance ability of the fluid also decreases.
Poly glycol type fluids are 2 times less compressible than silicone type fluids, even when heated. Less compressibility of brake fluid will increase pedal feel. Changing fluid on a regular basis will greatly increase the performance of the brake system.
FLUID SPECIFICATIONS All brake fluids must meet federal standard #116. Under this standard is three Department of Transportation (DOT) minimal specifications for brake fluid. They are DOT 3, DOT 4, and DOT 5.1 (for fluids based with Polyalkylene Glycol Ether) and DOT 5 (for Silicone based fluids).
FWIW, My bike takes DOT4 and after 2 years the fluid turns greenish brown in the front caliper from water intrusion and the lever feel gets spongy. Once flushed it is back to normal.
Last edited by KBFXDLI; 02-13-2009 at 11:03 AM.
#25
02-13-2009, 11:09 AM
First, when the pads wear, by design the pistons remain in an extended position. Therefore, if you check fluid, it's naturally going to look low due to the fact of the additional fluid needed to occupy the additional space in the calipers. Topping off a master cylinder at that time will make them overfull when the pistons are pushed back during a brake pad replacement and/or tire change.
#27
02-13-2009, 02:06 PM
Ron [quote]
No, technically IT DOESN"T. That's why fluids are used in hydralic application, for it's ability to transfer forces without being compressed. Physics 101. Fluids can contract and expand or change states with changes in temperature but cannot be compressed. You could actualy use water instead of brake fluid but it wouldn't last long as it would cause corrosion and wear as it has no lublication qualities, would freeze at low temps and would boil at high temps causing buddles of air which in turn can be compressed. That conversion to a gas is what would cause spongy brakes.
If water makes it into the system, you would need to do more than just change fluid because that would indicate a faulty seal or gasket and surely you'd see a fluid leak or seeping somewhere.
If it ain't broke, don't fix it.JMO
#28
02-13-2009, 02:45 PM
[QUOTE=Wecroft;4547270][quote 07:57 PMrbabosTechnically it does, but about the same as brake fluid. Forgot the number but it is freakishly, rediculously small in amount and meaninless.
Ron
No, technically IT DOESN"T. That's why fluids are used in hydralic application, for it's ability to transfer forces without being compressed. Physics 101. Fluids can contract and expand or change states with changes in temperature but cannot be compressed. You could actualy use water instead of brake fluid but it wouldn't last long as it would cause corrosion and wear as it has no lublication qualities, would freeze at low temps and would boil at high temps causing buddles of air which in turn can be compressed. That conversion to a gas is what would cause spongy brakes.
If water makes it into the system, you would need to do more than just change fluid because that would indicate a faulty seal or gasket and surely you'd see a fluid leak or seeping somewhere.
If it ain't broke, don't fix it.JMO
The compressibility of water is a function of pressure and temperature. At 0 °C in the limit of zero pressure the compressibility is 5.1×10-5 bar−1. In the zero pressure limit the compressibility reaches a minimum of 4.4×10-5 bar−1 around 45 °C before increasing again with increasing temperature. As the pressure is increased the compressibility decreases, being 3.9×10-5 bar−1 at 0 °C and 1000 bar. The bulk modulus of water is 2.2×109 Pa. The low compressibility of non-gases, and of water in particular, leads to them often being incorrectly labelled as incompressible. The low compressibility of water means that even in the deep oceans at 4000 m depth, where pressures are 4×107 Pa, there is only a 1.8% decrease in volume. Like I said, it is so small it is incorrectly termed as none compressible but to be scientifically correct it is. Would you feel it in the system, hell no.
Ron
Ron
No, technically IT DOESN"T. That's why fluids are used in hydralic application, for it's ability to transfer forces without being compressed. Physics 101. Fluids can contract and expand or change states with changes in temperature but cannot be compressed. You could actualy use water instead of brake fluid but it wouldn't last long as it would cause corrosion and wear as it has no lublication qualities, would freeze at low temps and would boil at high temps causing buddles of air which in turn can be compressed. That conversion to a gas is what would cause spongy brakes.
If water makes it into the system, you would need to do more than just change fluid because that would indicate a faulty seal or gasket and surely you'd see a fluid leak or seeping somewhere.
If it ain't broke, don't fix it.JMO
Ron
Last edited by rbabos; 02-13-2009 at 02:49 PM.
#29
02-13-2009, 07:10 PM
Originally Posted by [SIZE=4
KBFXDLI;[/SIZE]4542796] Go bleed your front caliper and you will see how much deterioration the brake fluid goes through. Water finds its way in and that does compress and degenerates your brake performance. My bike takes Dot4 which degrades 2x faster than Dot5. Same with the cars. They get flushed with every re-line.
Ron,
Here's where it all started. And yes, if you ride your bike at 4,000 meters below the surface of the ocean, you there will be a 1.8% degrease in volume, so that's what, about 6 drops? It won't be the only thing that gets compressed. You would still be unable to compress water with the little force produced by a master cylinder. P.S. Glass is still a fluid with a very low viscosity.
#30
02-13-2009, 07:37 PM
[quote=rbabos;4547468]
What he said
[quote 07:57 PMrbabosTechnically it does, but about the same as brake fluid. Forgot the number but it is freakishly, rediculously small in amount and meaninless.
Ron
The compressibility of water is a function of pressure and temperature. At 0 °C in the limit of zero pressure the compressibility is 5.1×10-5 bar−1. In the zero pressure limit the compressibility reaches a minimum of 4.4×10-5 bar−1 around 45 °C before increasing again with increasing temperature. As the pressure is increased the compressibility decreases, being 3.9×10-5 bar−1 at 0 °C and 1000 bar. The bulk modulus of water is 2.2×109 Pa. The low compressibility of non-gases, and of water in particular, leads to them often being incorrectly labelled as incompressible. The low compressibility of water means that even in the deep oceans at 4000 m depth, where pressures are 4×107 Pa, there is only a 1.8% decrease in volume. Like I said, it is so small it is incorrectly termed as none compressible but to be scientifically correct it is. Would you feel it in the system, hell no.
Ron
Ron
The compressibility of water is a function of pressure and temperature. At 0 °C in the limit of zero pressure the compressibility is 5.1×10-5 bar−1. In the zero pressure limit the compressibility reaches a minimum of 4.4×10-5 bar−1 around 45 °C before increasing again with increasing temperature. As the pressure is increased the compressibility decreases, being 3.9×10-5 bar−1 at 0 °C and 1000 bar. The bulk modulus of water is 2.2×109 Pa. The low compressibility of non-gases, and of water in particular, leads to them often being incorrectly labelled as incompressible. The low compressibility of water means that even in the deep oceans at 4000 m depth, where pressures are 4×107 Pa, there is only a 1.8% decrease in volume. Like I said, it is so small it is incorrectly termed as none compressible but to be scientifically correct it is. Would you feel it in the system, hell no.
Ron