Brake Flush Every 2 years
02-15-2019, 02:03 PM
#31
Three Wheelin'
Lot's of interesting opinions.
The bottom line is that we replace brake fluid to maintain a low boiling point. A low boiling point is mostly needed for repeated heavy use of the brakes. Obviously this occurs on a race track, but it can also occur with a spirited drive in the mountains. Many years ago when I had a new 914, I was young and ignorant, and went about 6 years on the same brake fluid. All was fine until I went for a hard drive in the Carolina mountains. The brakes faded out, but I was able to slow it down enough and drive for a few miles without using the brakes to cool them down, and they came right back.
So, as a much older and hopefully wiser fellow, I change my fluid before every track event, and make sure any car I drive in the mountains has reasonably fresh fluid. For a single panic stop event, I don't think it is so critical, but it sure can't hurt.
The brake fluds we use now are not all equal either. I normally use Motul 660, but my race car prep shop keeps saying I should try this Castrol fluid that they say is good for a whole race season. It does have a very high wet boiling point of about 520 F. It is pretty expensive, as Pegasus sells it for about $ 70.00 a bottle, so this may be the closest thing there is to a lifetime fill fluid:
The bottom line is that we replace brake fluid to maintain a low boiling point. A low boiling point is mostly needed for repeated heavy use of the brakes. Obviously this occurs on a race track, but it can also occur with a spirited drive in the mountains. Many years ago when I had a new 914, I was young and ignorant, and went about 6 years on the same brake fluid. All was fine until I went for a hard drive in the Carolina mountains. The brakes faded out, but I was able to slow it down enough and drive for a few miles without using the brakes to cool them down, and they came right back.
So, as a much older and hopefully wiser fellow, I change my fluid before every track event, and make sure any car I drive in the mountains has reasonably fresh fluid. For a single panic stop event, I don't think it is so critical, but it sure can't hurt.
The brake fluds we use now are not all equal either. I normally use Motul 660, but my race car prep shop keeps saying I should try this Castrol fluid that they say is good for a whole race season. It does have a very high wet boiling point of about 520 F. It is pretty expensive, as Pegasus sells it for about $ 70.00 a bottle, so this may be the closest thing there is to a lifetime fill fluid:
I use SRF all season, ~15-20 days. I'll bleed depending on the track and temps, but I don't flush.
SRF is great and saves a lot time if you do your own maint.
02-16-2019, 03:20 AM
#32
Single stop performance will not be affected, main risk is long downhill were operator (wife) relies only on brakes to moderate speed.
Also as noted timely fluid flushes protect against corrosion.
You can definitely go longer than two years but I would not go too much more.
Also as noted timely fluid flushes protect against corrosion.
You can definitely go longer than two years but I would not go too much more.
02-16-2019, 07:25 AM
#33
Burning Brakes
S^This. The brakes heat and cool, and condensation gets pulled past the seals. Not much, but it builds over time. The brakes may work fine unless and until they are called upon to do repeated stops. You don’t want to find out the hard way where the line is drawn. Also, the moisture will corrode brake components. I admit I track, so it’s every year for me.
02-16-2019, 07:50 AM
#34
Rocky Mountain High
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You can drive further than Porsche recommends between oil changes if you choose. Or if you don’t drive much and you hit the the time limit that Porsche recommends for an oil change, you can wait. It should be fine.
02-16-2019, 08:18 AM
#35
I get concerned about significantly raising the fluid boiling point above OEM fluid because the OEM fluid may be acting like a “fuse” to avoid damaging other OEM components. Certainly avoiding boiling is the goal but shouldn’t other upgrades (better ventilation?) be pursed as well, for track driving?
02-16-2019, 09:09 AM
#36
Other upgrades for track driving—absolutely! Most people end up changing to slotted rather than drilled rotors, track performance brake pads, studs to replace caliper bolts, and optimizing ventilation, as you say.
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Zhao (12-14-2020)
12-14-2020, 04:27 AM
#37
Drifting
Better ventilation would be nice.
I flush my fluid about once a year on my race car, and do minor bleeds in-between race weekends or as needed. I've done 24 hour endurance racing and no issues there. minor bleed after, fluid wasn't even terrible, and good to go. Even on a track where the main straight was about 30 seconds long between apexes (Temp airport track built just for indycar racing) into a 80kph or so 120 degree corner... so huge time spent on the brakes... the fluid was pretty much fine when I blend it. However, I did end up with no brakes once in a race from boiled (550f) fluid, and that was on a tight low speed track with almost no straights when I was drafting off someone's *** for 10 minutes+ straight. I wasn't the only one that lost brakes on that track either at that event. So ventilation would be great if you can improve it because better airflow can only help, but I think for most cars it's not necessary because on almost every race track there is ample time to cool the brakes in-between corners to prevent boiling the fluid. Generally speaking, if someone is having braking problems and boiling good fluid it's probably because of their driving and most likely they're slowing down too much. That's usually the problem with people that complain about brake problems at lapping events from my experience, and that is usually an auto correcting problem as they drive faster.
As for high temp component wear, I also only saw one downside to high temps on braking components, and that is it cooked and disintegrated the rubber on some rebuilt brake calipers I had. Obviously the rebuild kit used inferior materials vs OEM, because I've never seen a problem with OEM brake components from putting a lot of heat into them. I have a race car with 35 year old original calipers that has close to 10000km of hard racing on it and no issues. Upgrading the brakes beyond good fluid, proper race pads, a bias controller, and ventilation is just not something I ever see people do on their race cars, so I wouldn't worry about anything else. I also usually use something in the 500-550 temp range (like ford brake fluid because it's very cheap and I know I don't need anything higher temp) which I consider around the minimum for racing/lapping. High HP cars may require higher temp fluid than low hp cars. I'd say component wear from heat is a non-issue.
I also do not think it is necessary to change fluid on daily drivers as often as some people claim needs to happen (for example there is a lexus dealer where I am that tries to push for 20000km fluid flushes). Realistically a lot of people are driving on the street who haven't had a brake fluid fluid since their car was off warranty. 10, 20 year old cars, and what's surprising is the moisture content often tests ok. I'll bleed and most likely flush fluid on a daily driver when I change the brake pads, and I think that is overkill already. 2 year brake fluid flush recommendations are sponsored by service departments and brake fluid manufacturers, who want to sell you a product/service.
It's just like child car seat manufacturers who say their seats need to be changed in an accident, no matter how minor. You can't tell me a lump of hard plastic and cloth is now a death trap from a 10kph bumper tap in a parking lot. If that was the case every time your car hits a pot hole you should change it as well. Their goal is to sell more car seats.
I flush my fluid about once a year on my race car, and do minor bleeds in-between race weekends or as needed. I've done 24 hour endurance racing and no issues there. minor bleed after, fluid wasn't even terrible, and good to go. Even on a track where the main straight was about 30 seconds long between apexes (Temp airport track built just for indycar racing) into a 80kph or so 120 degree corner... so huge time spent on the brakes... the fluid was pretty much fine when I blend it. However, I did end up with no brakes once in a race from boiled (550f) fluid, and that was on a tight low speed track with almost no straights when I was drafting off someone's *** for 10 minutes+ straight. I wasn't the only one that lost brakes on that track either at that event. So ventilation would be great if you can improve it because better airflow can only help, but I think for most cars it's not necessary because on almost every race track there is ample time to cool the brakes in-between corners to prevent boiling the fluid. Generally speaking, if someone is having braking problems and boiling good fluid it's probably because of their driving and most likely they're slowing down too much. That's usually the problem with people that complain about brake problems at lapping events from my experience, and that is usually an auto correcting problem as they drive faster.
As for high temp component wear, I also only saw one downside to high temps on braking components, and that is it cooked and disintegrated the rubber on some rebuilt brake calipers I had. Obviously the rebuild kit used inferior materials vs OEM, because I've never seen a problem with OEM brake components from putting a lot of heat into them. I have a race car with 35 year old original calipers that has close to 10000km of hard racing on it and no issues. Upgrading the brakes beyond good fluid, proper race pads, a bias controller, and ventilation is just not something I ever see people do on their race cars, so I wouldn't worry about anything else. I also usually use something in the 500-550 temp range (like ford brake fluid because it's very cheap and I know I don't need anything higher temp) which I consider around the minimum for racing/lapping. High HP cars may require higher temp fluid than low hp cars. I'd say component wear from heat is a non-issue.
I also do not think it is necessary to change fluid on daily drivers as often as some people claim needs to happen (for example there is a lexus dealer where I am that tries to push for 20000km fluid flushes). Realistically a lot of people are driving on the street who haven't had a brake fluid fluid since their car was off warranty. 10, 20 year old cars, and what's surprising is the moisture content often tests ok. I'll bleed and most likely flush fluid on a daily driver when I change the brake pads, and I think that is overkill already. 2 year brake fluid flush recommendations are sponsored by service departments and brake fluid manufacturers, who want to sell you a product/service.
It's just like child car seat manufacturers who say their seats need to be changed in an accident, no matter how minor. You can't tell me a lump of hard plastic and cloth is now a death trap from a 10kph bumper tap in a parking lot. If that was the case every time your car hits a pot hole you should change it as well. Their goal is to sell more car seats.
Last edited by Zhao; 12-14-2020 at 04:30 AM.
12-22-2020, 10:20 PM
#38
To me it’s like flushing your air in your tires
12-22-2020, 10:45 PM
#39
RL Community Team
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996AE (12-23-2020)
12-23-2020, 12:06 AM
#40
RL Community Team
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The system is not really closed. Every time you take off the reservoir cap, moisture from the atmosphere is introduced to the system. I suspect this is why newer cars use see through reservoirs to eliminate the need to open the cap to check fluid level.
Below is a chart which shows the average percentage of water in DOT 3 brake fluid as it ages:
Below is a chart which shows the average percentage of water in DOT 3 brake fluid as it ages:
12-23-2020, 06:05 AM
#41
Nordschleife Master
And the question is - when you take it to the dealer and tell them to change the brake fluid after 2 years, do they actually do it? I think they test it and if it is OK, they do not change it but charge you for it. '
Yeah, I am a cynic.
Yeah, I am a cynic.
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12-23-2020, 02:22 PM
#42
Intermediate
Can someone confirm if the results of a water content test at the brake fluid reservoir would be consistent with the contents located in the brake lines. I'm not sure how much fluid turnover there is in the lines and my concern would be getting two different results (reservoir vs brake lines) depending on where the test was conducted.
12-23-2020, 04:22 PM
#43
Burning Brakes
The brake system is not a totally closed system. It's designed to allow some air in. There is always some degradation/contamination building up in the brake fluid over time. Under normal (not racing/high performance) driving you can probably get away with letting the two year cycle slip a little (6 to 12 months?). However, in an emergency situation I'd want to know that my brakes are working at their very best. To me, it's not worth the trade off of saving a few dollars vs. saving a life...just sayin'. 
12-23-2020, 08:25 PM
#44
RL Community Team
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Sorry people. The hydraulic brake systems in in all cars are completely sealed from the outside air. There are rubber diaphragms/bladders in the reservoir cap and valves in the master cylinder that expand and contract with the hydraulic action keeping the system pressure balanced.
If the system was constantly exposed to the air as some folks suggest the brake fluid would absorb so much water so quickly it would need to be changed every week.
Don't believe me? Google it.
If the system was constantly exposed to the air as some folks suggest the brake fluid would absorb so much water so quickly it would need to be changed every week.
Don't believe me? Google it.
12-23-2020, 08:41 PM
#45
RL Community Team
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How fast does brake fluid absorb moisture?
It depends on the fluid and environment. A typical high performance DOT 4 fluid like, Motul, AP, Castrol SRF, Wilwood and ATE SuperBlue, in a high humdity evironment will absorb as much as 4.5-5% moisture in as short a period as 2 weeks. In real world testing (several daily driver cars, Prospeed GS610™ absorbed <1% moisture in 3 years. This was measured from the brake fluid in the resevoir where the vehicle's brake system is most likly to contain the greatest contaimination of moisture.
How does brake fluid become contaminated?
Water/moisture can be found in nearly all brake systems. Moisture enters the brake system in several ways. One of the more common ways is from using old or pre-opened fluid. Keep in mind, that brake fluid draws in moisture from the surrounding air. Tightly sealing brake fluid bottles and not storing them for long periods of time will help keep moisture out. When changing or bleeding brake fluid always replace master cylinder caps as soon as possible to prevent moisture from entering into the master cylinder. Condensation, (small moisture droplets) can form in lines and calipers. As caliper and line temperatures heat up and then cool repeatedly, condensation occurs, leaving behind an increase in moisture/water. Over time the moisture becomes trapped in the internal sections of calipers, lines, master cylinders, etc. When this water reaches 212º F the water turns to steam. Many times air in the brake system is a result of water that has turned to steam. The build up of steam will create air pressure in the system, sometimes to the point that enough pressure is created to push caliper pistons into the brake pad. This will create brake drag as the rotor and pads make contact and can also create more heat in the system. Diffusion is another way in that water/moisture may enter the system.
Diffusion occurs when over time moisture enters through rubber brake hoses. The use of hoses made from EPDM materials (Ethlene-Propylene-Diene-Materials) will reduce the amount of diffusion OR use stainless steel braided brake hose with a non-rubber sleeve (usually Teflon) to greatly reduce the diffusion process.
It depends on the fluid and environment. A typical high performance DOT 4 fluid like, Motul, AP, Castrol SRF, Wilwood and ATE SuperBlue, in a high humdity evironment will absorb as much as 4.5-5% moisture in as short a period as 2 weeks. In real world testing (several daily driver cars, Prospeed GS610™ absorbed <1% moisture in 3 years. This was measured from the brake fluid in the resevoir where the vehicle's brake system is most likly to contain the greatest contaimination of moisture.
How does brake fluid become contaminated?
Water/moisture can be found in nearly all brake systems. Moisture enters the brake system in several ways. One of the more common ways is from using old or pre-opened fluid. Keep in mind, that brake fluid draws in moisture from the surrounding air. Tightly sealing brake fluid bottles and not storing them for long periods of time will help keep moisture out. When changing or bleeding brake fluid always replace master cylinder caps as soon as possible to prevent moisture from entering into the master cylinder. Condensation, (small moisture droplets) can form in lines and calipers. As caliper and line temperatures heat up and then cool repeatedly, condensation occurs, leaving behind an increase in moisture/water. Over time the moisture becomes trapped in the internal sections of calipers, lines, master cylinders, etc. When this water reaches 212º F the water turns to steam. Many times air in the brake system is a result of water that has turned to steam. The build up of steam will create air pressure in the system, sometimes to the point that enough pressure is created to push caliper pistons into the brake pad. This will create brake drag as the rotor and pads make contact and can also create more heat in the system. Diffusion is another way in that water/moisture may enter the system.
Diffusion occurs when over time moisture enters through rubber brake hoses. The use of hoses made from EPDM materials (Ethlene-Propylene-Diene-Materials) will reduce the amount of diffusion OR use stainless steel braided brake hose with a non-rubber sleeve (usually Teflon) to greatly reduce the diffusion process.