Time for a change...???
Discussion
Hi all,
With all the recent threads regarding braking and clutch system efficiencies, I thought I'd inject a little advise on a sorely overlooked maintenance procedure. Namely, the importance of changing your car's brake fluid on a regular interval of no longer than every other driving season or two years, but preferably every year for the average Lotus owner.
The importance of this cannot be overstated as moisture ridden brake fluid can lead to accelerated deterioration of the rubber seals, corrosion of the lines and bores of the calipers, slaves and Master Cylinders, poor braking performance and worst case, total brake failure .
A brake fluid needs to maintain it's liquid state at high temps to insure that sufficient force from your foot on the brake pedal is transmitted to the calipers via the fluid to actuate the calipers and stop the car. If the fluid boils and becomes a gas, most of the pedal effort is wasted compressing the gas and not actuating the calipers.
The properties needed by a good brake fluid are; It must not boil under high temperatures, it must retain it's viscosity at temps at or below freezing, it must not readily compress, it must flow easily through small gauge orifices, it must not corrode or react with materials in the braking system, it must be able to lubricate the moving, metallic and rubber parts of the brake system, it must remain chemically stable for extended periods of time, it must be miscible with other similar products (mix with), it must not form other compounds such as sludge or gum in the brake system.
Brake fluids fall into two main categories, mineral and silicone and are rated by the US Dept. of Transportation based upon the minimum temperature, expressed in degrees Farenheit (F°), of both their WET (2% moisture content) and DRY boiling points. These ratings are: DOT #2, #3, #4, #5.
These boiling points are important because as the fluid resists being compressed by the master cylinder, it becomes hot. In addition, a great deal of heat, which is generated by the brake action of the pads against the discs, is transferred to the fluid as well. The brake discs can generate heat in excess of 1,300°F and transfer as much as a third of this heat to the brake fluid in the process.
DOT #2 is based on the oil from the Caster Bean and is for use with Drum Brakes, as such it is really obsolete. It's DRY boiling point is a minimum of 374°F
Dot #3 and #4 are composed of Polyalkalene Glycol Ether, a characteristic of which is it's strong attraction to water. It is said to be hygroscopic. Water contaminating Brake Fluid makes it's boiling point drop which causes bubbles and steam to form in the Brake System. These are more compressible than Brake Fluid which makes it more difficult for the Master Cylinder to transfer the energy from the brake pedal to compress the calipers. This can cause a spongy, soft feel and can, in the worst case, use all the energy of the brake pedal to compress the bubbles and steam leaving none to compress the calipers at all resulting in total brake failure . DOT #3 has a DRY boiling point of 401°F and a WET boiling Point of 284°F. DOT #4 has a DRY boiling point of 446°F and a WET boiling point of 311°F. Remember, these are minimums allowed by the US DOT.
DOT #5 is silicone fluid, and while it isn't hygroscopic at all, it is lighter than water. So, any water migrating into the system will flow to the lowest point, namely the calipers. Once there, it can boil at 212°F, cause a vapor lock and cause total brake failure. DOT #5 is expensive and should be changed annually to avoid moisture problems, so it's just not practical. It's Dry boiling point is 500°F and it's WET boiling point is 356°F.
Water is bad for your brakes. As little as 2% moisture contamination can reduce the boiling point by as much as 25%. Independent field tests by the SAE (Society of Automotive Engineers) have shown that the average 12 month old car has a moisture content of 2% in the brake fluid. On cars 18 months old, the level averaged 3% with a quarter of the cars tested being over 4%. After several years, moisture content levels of 7% or 8% are common. To put this into perspective, DOT #4 is rated at greater than 446°F, add 3% moisture content and the temp drops to under 300°F, at anything more than 4%, you might just as well be running pure water through the system.
How does water get into the brake system? Moisture can migrate through the microscopic pores in the rubber brake hoses and seals and especially when the reservoir cap is opened. The hygroscopic quality of the fluid will literally pull the moisture out of the air. Also, each time you apply your brakes or clutch, some moisture enters the weep hole in the cap of the reservoir.
The recommended Brake Fluid for Lotus cars is Castrol GT LMA. It is rated as DOT #4 with a DRY boiling point of 446°F and a WET boiling point of 311°F. The 'LMA' stands for 'Low Moisture Acivity' and has a very slightly higher resistance to moisture than regular DOT #4 fluids. It is said to extend the life of the seals in the braking system, but the only evidence of this is anecdotal, there have been no definitive tests on this.
You can also substitute Castrol SRF which has a Dry boiling point of 590°F and a WET boiling point of 518°F and is rated DOT #5. It does not have the moisture resisting qualities of LMA and costs about $75USD per liter, so unless you're constantly on the track, stick with the Castrol GT LMA.
Most car companies recommend a fluid change every two years, but this is for regular use. If your driving is more severe, less frequent, or you live in a humid climate, you should change the fluid every year to maximise the system's braking effect and the longevity of the components. Happy Motoring! Jim'85TE
With all the recent threads regarding braking and clutch system efficiencies, I thought I'd inject a little advise on a sorely overlooked maintenance procedure. Namely, the importance of changing your car's brake fluid on a regular interval of no longer than every other driving season or two years, but preferably every year for the average Lotus owner.
The importance of this cannot be overstated as moisture ridden brake fluid can lead to accelerated deterioration of the rubber seals, corrosion of the lines and bores of the calipers, slaves and Master Cylinders, poor braking performance and worst case, total brake failure .
A brake fluid needs to maintain it's liquid state at high temps to insure that sufficient force from your foot on the brake pedal is transmitted to the calipers via the fluid to actuate the calipers and stop the car. If the fluid boils and becomes a gas, most of the pedal effort is wasted compressing the gas and not actuating the calipers.
The properties needed by a good brake fluid are; It must not boil under high temperatures, it must retain it's viscosity at temps at or below freezing, it must not readily compress, it must flow easily through small gauge orifices, it must not corrode or react with materials in the braking system, it must be able to lubricate the moving, metallic and rubber parts of the brake system, it must remain chemically stable for extended periods of time, it must be miscible with other similar products (mix with), it must not form other compounds such as sludge or gum in the brake system.
Brake fluids fall into two main categories, mineral and silicone and are rated by the US Dept. of Transportation based upon the minimum temperature, expressed in degrees Farenheit (F°), of both their WET (2% moisture content) and DRY boiling points. These ratings are: DOT #2, #3, #4, #5.
These boiling points are important because as the fluid resists being compressed by the master cylinder, it becomes hot. In addition, a great deal of heat, which is generated by the brake action of the pads against the discs, is transferred to the fluid as well. The brake discs can generate heat in excess of 1,300°F and transfer as much as a third of this heat to the brake fluid in the process.
DOT #2 is based on the oil from the Caster Bean and is for use with Drum Brakes, as such it is really obsolete. It's DRY boiling point is a minimum of 374°F
Dot #3 and #4 are composed of Polyalkalene Glycol Ether, a characteristic of which is it's strong attraction to water. It is said to be hygroscopic. Water contaminating Brake Fluid makes it's boiling point drop which causes bubbles and steam to form in the Brake System. These are more compressible than Brake Fluid which makes it more difficult for the Master Cylinder to transfer the energy from the brake pedal to compress the calipers. This can cause a spongy, soft feel and can, in the worst case, use all the energy of the brake pedal to compress the bubbles and steam leaving none to compress the calipers at all resulting in total brake failure . DOT #3 has a DRY boiling point of 401°F and a WET boiling Point of 284°F. DOT #4 has a DRY boiling point of 446°F and a WET boiling point of 311°F. Remember, these are minimums allowed by the US DOT.
DOT #5 is silicone fluid, and while it isn't hygroscopic at all, it is lighter than water. So, any water migrating into the system will flow to the lowest point, namely the calipers. Once there, it can boil at 212°F, cause a vapor lock and cause total brake failure. DOT #5 is expensive and should be changed annually to avoid moisture problems, so it's just not practical. It's Dry boiling point is 500°F and it's WET boiling point is 356°F.
Water is bad for your brakes. As little as 2% moisture contamination can reduce the boiling point by as much as 25%. Independent field tests by the SAE (Society of Automotive Engineers) have shown that the average 12 month old car has a moisture content of 2% in the brake fluid. On cars 18 months old, the level averaged 3% with a quarter of the cars tested being over 4%. After several years, moisture content levels of 7% or 8% are common. To put this into perspective, DOT #4 is rated at greater than 446°F, add 3% moisture content and the temp drops to under 300°F, at anything more than 4%, you might just as well be running pure water through the system.
How does water get into the brake system? Moisture can migrate through the microscopic pores in the rubber brake hoses and seals and especially when the reservoir cap is opened. The hygroscopic quality of the fluid will literally pull the moisture out of the air. Also, each time you apply your brakes or clutch, some moisture enters the weep hole in the cap of the reservoir.
The recommended Brake Fluid for Lotus cars is Castrol GT LMA. It is rated as DOT #4 with a DRY boiling point of 446°F and a WET boiling point of 311°F. The 'LMA' stands for 'Low Moisture Acivity' and has a very slightly higher resistance to moisture than regular DOT #4 fluids. It is said to extend the life of the seals in the braking system, but the only evidence of this is anecdotal, there have been no definitive tests on this.
You can also substitute Castrol SRF which has a Dry boiling point of 590°F and a WET boiling point of 518°F and is rated DOT #5. It does not have the moisture resisting qualities of LMA and costs about $75USD per liter, so unless you're constantly on the track, stick with the Castrol GT LMA.
Most car companies recommend a fluid change every two years, but this is for regular use. If your driving is more severe, less frequent, or you live in a humid climate, you should change the fluid every year to maximise the system's braking effect and the longevity of the components. Happy Motoring! Jim'85TE
Great write-up!
Small addition though..
DOT5 is indeed silicone based and should *never* be mixed with glycol based brake fluids. It can also attack rubber seals meant for glycol based brake systems.
Silicone DOT5 has one very nasty propery: it expands significantly under heat (and gets more compressable too).
When used in brake systems that were not specifically designed for it's use, this expansion can make the brakes apply themselves (or rather, not release when you want to)
DOT5.1, however, is glycol based and can be used without issue in most brake systems that require DOT4 as a minimum.
Oh.. And changing your brake fluid regularly means you'll be fine when using cheap 'off the shelf' brake fluid (using the correct DOT type for your car). No need for hyper-expensive types in this case.
I use this pressure bleeder. Flushing the brake fluid is now a 30 minute job:
www.motiveproducts.com/
(No need for a spare tyre like the EZ-bleed)
Bye, Arno.
Small addition though..
DOT5 is indeed silicone based and should *never* be mixed with glycol based brake fluids. It can also attack rubber seals meant for glycol based brake systems.
Silicone DOT5 has one very nasty propery: it expands significantly under heat (and gets more compressable too).
When used in brake systems that were not specifically designed for it's use, this expansion can make the brakes apply themselves (or rather, not release when you want to)
DOT5.1, however, is glycol based and can be used without issue in most brake systems that require DOT4 as a minimum.
Oh.. And changing your brake fluid regularly means you'll be fine when using cheap 'off the shelf' brake fluid (using the correct DOT type for your car). No need for hyper-expensive types in this case.
I use this pressure bleeder. Flushing the brake fluid is now a 30 minute job:
www.motiveproducts.com/
(No need for a spare tyre like the EZ-bleed)
Bye, Arno.
Great input Jim!
One interesting thing I noted, speaking of fluid and seals. When I replaced a leaky master clutch cylinder, I went ahead and replaced my red hose with the SS clutch hose, and got a new aluminum slave as well. So everything was new. I ran quite a bit of fluid thru the system to make it clean and fresh. It was really neat to see clean clear fluid in there. After a few days, I was messing with the clutch adjustment at the slave and pushed the slave rod in a bit. I happened to double check the master cylinder (just in case I'd pushed some fluid out the top of the master by pressing on the slave rod, and I noticed it all black down below in the master... so I bled them again. I was surprized to see black stuff in there so soon. I used Castrol LMA. So, it will be at least yearly, if not sooner that I bleed everything.
- Mark901SE
One interesting thing I noted, speaking of fluid and seals. When I replaced a leaky master clutch cylinder, I went ahead and replaced my red hose with the SS clutch hose, and got a new aluminum slave as well. So everything was new. I ran quite a bit of fluid thru the system to make it clean and fresh. It was really neat to see clean clear fluid in there. After a few days, I was messing with the clutch adjustment at the slave and pushed the slave rod in a bit. I happened to double check the master cylinder (just in case I'd pushed some fluid out the top of the master by pressing on the slave rod, and I noticed it all black down below in the master... so I bled them again. I was surprized to see black stuff in there so soon. I used Castrol LMA. So, it will be at least yearly, if not sooner that I bleed everything.
- Mark901SE
ErnestM said:
Motul 600 is also good for brake fluid.
Special attention to your transmission oil (I use Redline MT90) is also not a bad idea...
ErnestM
Ernest,
Motul Racing 600 is indeed a very good Brake Fluid. It has a Dry boiling point of 585°F and a WET boiling point of 421°F.
The two problems with using Motul are firstly the expense. It is the second most expensive fluid next to Castrol SRF.
Secondly, to achieve such high boiling points, it has a much higher Glycol content than other mineral based fluids. This enhances it's hygroscopic quality and it absorbs moisture much more readily.
It was specifically designed for track use. Racers don't care about hygroscopicity as they change the fluid so often that this is no concern.
To use it in a street application, and maintain a moisture content of 2% or <, you would need to replace the fluid at intervals of no more than 6 mos. (probably 3 mos. in the humid clime you live in) this makes the fluid very expensive and inconvenient to use. If you don't change within this interval, the moisture content becomes such that the boiling points are reduced to levels under those of Castrol GT LMA, and you're not actually receiving the enhanced effectiveness you paid for anyway. Happy Motoring! Jim'85TE
Don't forget safety when working with brake fluid. At a minimum you should be wearing eye protection. Due to the hygroscopic nature of this stuff, it will suck the moisture right out of your skin.
According to MSDS sheets, the pH of brake fluid is between 7 and 11. One page had it listed as 9.5 - 10.5. High pH compounds are hard on the skin and worse on the eyes. One page listed corneal damage as a possibility. Probably accurate as the body has natural defenses against acids but not against bases.
I personally hate wearing rubber gloves so whenever I'm bleeding a system I'll put a bucket of water or hose about 10' away and wash frequently. Taking care of course to prevent contamination of the brake fluid with water.
Water bottles are great eye washes as well.
Finally, I recommend against wearing contacts while working with brake fluid (most fluids). The lenses won't react with the fluid but will make it more difficult to flush the eye.
Safety first, after all that is the reason for doing the job.
According to MSDS sheets, the pH of brake fluid is between 7 and 11. One page had it listed as 9.5 - 10.5. High pH compounds are hard on the skin and worse on the eyes. One page listed corneal damage as a possibility. Probably accurate as the body has natural defenses against acids but not against bases.
I personally hate wearing rubber gloves so whenever I'm bleeding a system I'll put a bucket of water or hose about 10' away and wash frequently. Taking care of course to prevent contamination of the brake fluid with water.
Water bottles are great eye washes as well.
Finally, I recommend against wearing contacts while working with brake fluid (most fluids). The lenses won't react with the fluid but will make it more difficult to flush the eye.
Safety first, after all that is the reason for doing the job.
okc-esprit said:
Don't forget safety when working with brake fluid. At a minimum you should be wearing eye protection. Due to the hygroscopic nature of this stuff, it will suck the moisture right out of your skin.
According to MSDS sheets, the pH of brake fluid is between 7 and 11. One page had it listed as 9.5 - 10.5. High pH compounds are hard on the skin and worse on the eyes. One page listed corneal damage as a possibility. Probably accurate as the body has natural defenses against acids but not against bases.
I personally hate wearing rubber gloves so whenever I'm bleeding a system I'll put a bucket of water or hose about 10' away and wash frequently. Taking care of course to prevent contamination of the brake fluid with water.
Water bottles are great eye washes as well.
Finally, I recommend against wearing contacts while working with brake fluid (most fluids). The lenses won't react with the fluid but will make it more difficult to flush the eye.
Safety first, after all that is the reason for doing the job.
OKC,
Oustanding Advise! Forgive me for not recommending 'Safety First'! Happy Motoring! Jim'85TE
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