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Discussion Starter · #1 ·
I'll be honest- I don't think I've ever replaced brake fluid in my life in any of my cars. I'm certain that my mechanics didn't replace/flush my brake fluids either. Never a problem. With my Porsche I'll be sure to follow their maintenance schedule though.

Do you Doityourselfers replace the brake/clutch/coolant as required? If you track your car I get it... the brake fluid needs replacement. Do you think the required replacement schedule is over aggressive? Maybe I've just been lucky!
 

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Brake fluid is hygroscopic. That means it absorbs moisture out of the air/atmosphere (regardless of miles). When you apply the brakes, it compresses the brake fluid to engage the pistons in the caliper, which then makes the brakes work.

If there's excess water in the brake fluid, as it heats up, it'll boil the the water turning it to steam. Steam compresses, which means there is no longer enough pressure to operate the pistons. Therefore, pedal goes to the floor, and there's no brakes!

A lot of people get away with it, but especially given the criticality of the braking system, I would strongly recommend having the fluid flushed every two years on every car. For a car that's tracked, I'd say a minimum of once a year, if not twice a year.
 

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Discussion Starter · #3 ·
Brake fluid is hygroscopic. That means it absorbs moisture out of the air/atmosphere (regardless of miles). When you apply the brakes, it compresses the brake fluid to engage the pistons in the caliper, which then makes the brakes work.

If there's excess water in the brake fluid, as it heats up, it'll boil the the water turning it to steam. Steam compresses, which means there is no longer enough pressure to operate the pistons. Therefore, pedal goes to the floor, and there's no brakes!

A lot of people get away with it, but especially given the criticality of the braking system, I would strongly recommend having the fluid flushed every two years on every car. For a car that's tracked, I'd say a minimum of once a year, if not twice a year.
Not going to argue. I guess the manufacturers know better than me for sure. But hoe exactly does moisture get into the brake lines? It’s a sealed system except the reservoir.
 

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Not going to argue. I guess the manufacturers know better than me for sure. But hoe exactly does moisture get into the brake lines? It’s a sealed system except the reservoir.
Good question and I don't know, but I suspect because the pistons in the brake calipers have to move that this might be a source of contact. One brake source stated: "brake fluid is hygroscopic by nature which means it absorbs water from the environment via seams and microscopic pores in your hydraulic lines" as a reason.
 
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If the reservoir is not sealed - could it not get in through the unsealed reservoir?
 

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With the help of a friend, I replaced the fluid in mine after year one with Castrol SRF before a track weekend. I’ll change it again after a year as it is easy to do.
 

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Brake fluid is hygroscopic. That means it absorbs moisture out of the air/atmosphere (regardless of miles). When you apply the brakes, it compresses the brake fluid to engage the pistons in the caliper, which then makes the brakes work.

If there's excess water in the brake fluid, as it heats up, it'll boil the the water turning it to steam. Steam compresses, which means there is no longer enough pressure to operate the pistons. Therefore, pedal goes to the floor, and there's no brakes!

A lot of people get away with it, but especially given the criticality of the braking system, I would strongly recommend having the fluid flushed every two years on every car. For a car that's tracked, I'd say a minimum of once a year, if not twice a year.
If u check the brake fluid with a tester and it shows no moisture in UR opinion do u have to change th fluid?
 

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If u check the brake fluid with a tester and it shows no moisture in UR opinion do u have to change th fluid?
I'm not familiar with brake fluid testers, but the very first question that popped into my head was "how accurate are they?"

For me personally, especially having experienced brake fluid failure on the track (and subsequent changing of the pants), it's such a relatively easy and inexpensive thing to do, I'd rather just flush the fluid for peace of mind. I'm fortunate to have a set of quick jacks, so I will typically do a full flush every spring, whenever I'm swapping over from winter to summer wheels/tires. By myself, I can usually get it done in 60-90 minutes.

Depending on how many events I've done in the year, I'll do a quick corner bleed of each caliper just to get fresher fluid into the caliper itself, and top up the reservoir.
 

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You track the car, you change to racing brake fluid and change it every two years. Steam bubbles is nothing to trifle with.

If you don't track the car, it is prudent to do it every two years for regular fluid. I think most of us have experienced the occasional mountain descent where you ride the brakes for miles... My indie mechanic for the wife's BMW has a limit of 5 years, if you don't track it.

Rust due to water in the lines sounds like and old wife's tale... I wouldn't consider it a reason for doing it.

YMMV
 

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I'm not familiar with brake fluid testers, but the very first question that popped into my head was "how accurate are they?"

For me personally, especially having experienced brake fluid failure on the track (and subsequent changing of the pants), it's such a relatively easy and inexpensive thing to do, I'd rather just flush the fluid for peace of mind. I'm fortunate to have a set of quick jacks, so I will typically do a full flush every spring, whenever I'm swapping over from winter to summer wheels/tires. By myself, I can usually get it done in 60-90 minutes.

Depending on how many events I've done in the year, I'll do a quick corner bleed of each caliper just to get fresher fluid into the caliper itself, and top up the reservoir.
I got this tip from the MACAN forum.
it seems that for the everyday driver not tracking the car there is no need to change the brake fluid.
it also seems that the tester is a simple accurate device
the service guy seemed to agree with me.
the $1200 quoted $ for the 20000 mile service wound up at $325.
When all the unesseary Stuff including $65 oil additive was removed
 

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I got this tip from the MACAN forum.
it seems that for the everyday driver not tracking the car there is no need to change the brake fluid.
it also seems that the tester is a simple accurate device
the service guy seemed to agree with me.
the $1200 quoted $ for the 20000 mile service wound up at $325.
When all the unesseary Stuff including $65 oil additive was removed
I would strongly disagree with that. Like others have mentioned, moisture builds up in brake fluid over time and can degrade the ability of the car to brake. This isnt just some Porsche requirement either, virtually ever vehicle calls for regular brake fluid changes for this very reason. Spending a few hundred bucks ever 2 years to ensure the brake system is functioning properly doesnt seem like a big deal to me.
 

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I would strongly disagree with that. Like others have mentioned, moisture builds up in brake fluid over time and can degrade the ability of the car to brake. This isnt just some Porsche requirement either, virtually ever vehicle calls for regular brake fluid changes for this very reason. Spending a few hundred bucks ever 2 years to ensure the brake system is functioning properly doesnt seem like a big deal to me.
I disagree with your disagreement!...:D

Unless you bring the temperature of the calipers to the level that the mixture of brake fluid/water will boil, there should not be any degradation in the brake function. The brake fluid/water mixture in the liquid phase is incompressible.

Note that I said brake fluid/water mixture boiling. That temperature must be well above 212F. I expect that in normal driving you probably never reach it, otherwise we would be having Chevys and Kias crashing into each other downtown.

Now, doing a 10 mi. downhill in a Hyundai Elantra back in the nineties, I had brakes squealing and smoking like they were on fire. I can't vouch how much longer before I 'd have a break fluid boilover (it was a very badly maintained 5 yo rental) but I stopped to cool off the drum brakes in the back...
 

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I never understood why so many people think they're smarter than the engineers that do this for a living.

I'll continue to replace the brake fluid in each of my vehicles no less than every two years. The braking system is kind of important.
 

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I would strongly disagree with that. Like others have mentioned, moisture builds up in brake fluid over time and can degrade the ability of the car to brake. This isnt just some Porsche requirement either, virtually ever vehicle calls for regular brake fluid changes for this very reason. Spending a few hundred bucks ever 2 years to ensure the brake system is functioning properly doesnt seem like a big deal to me.
I’m so sensitive to dealer $ I check over everything
i will reconsider on my next service
thanks
 

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If the reservoir is not sealed - could it not get in through the unsealed reservoir?
Yes it does.
Also the heat cool cycles draw small amounts of moisture through and microscopic pores in the hydraulic system.
 

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Two points, from my perspective:
  • @alanhats20: If you're so worried about dealer-service markup, have the brake fluid replaced at an independent service shop. Brakes are not Porsche-specific things. Any place can do it (though I'd choose a shop that has Porsche experience). You'll likely pay roughly half what a dealer would charge.
  • Most street motorcycles do NOT have the cross-axle dual-circuit redundancy that four-wheel road vehicles must have because, well, it's physically imposssible. What bikes have are two completely independent braking systems - one for the front wheel, and one for the rear. Yet the very same every-two-years-no-matter-what rule for replacing brake fluid applies to bikes. Why is that? Because brake fluid degrades over time, no matter how often the bike is ridden - and anyone who's squeezed a brake lever on a bike that's been sitting in a garage for years upon years can attest to this.
Don't take chances with brakes. Just do it.
 

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Two points, from my perspective:
  • @alanhats20: If you're so worried about dealer-service markup, have the brake fluid replaced at an independent service shop. Brakes are not Porsche-specific things. Any place can do it (though I'd choose a shop that has Porsche experience). You'll likely pay roughly half what a dealer would charge.
  • Most street motorcycles do NOT have the cross-axle dual-circuit redundancy that four-wheel road vehicles must have because, well, it's physically imposssible. What bikes have are two completely independent braking systems - one for the front wheel, and one for the rear. Yet the very same every-two-years-no-matter-what rule for replacing brake fluid applies to bikes. Why is that? Because brake fluid degrades over time, no matter how often the bike is ridden - and anyone who's squeezed a brake lever on a bike that's been sitting in a garage for years upon years can attest to this.
Don't take chances with brakes. Just do it.
So regardless of the mileag, time is the determination on brake fluid
thanks
 

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....... snip.............. Spending a few hundred bucks ever 2 years to ensure the brake system is functioning properly doesnt seem like a big deal to me.
I'm with you on changing fluid, but it need not cost hundreds of dollars for those with even minimal DIY mechanical skills. I'm guessing many people posting here have never owned a clunker as a daily driver or restored an old car. Fluid leaking from either old-school drum brake slave cylinders (can you still use the word "slave"?) or from ancient calipers is most often caused by corrosion. You pray that it's just caused by old, hard brake seals, but when you open things up you find pitting in the bore, so it's either hone or replace.

How can that happen in a system completely filled with what seems to be an oil-like fluid? Long term moisture, that's how. Moisture in brake fluid is real and will eventually lead to real problems. The prevention is pretty easy. Changing fluid once in a while is a relatively simple job. It's actually just extended brake bleeding, a process that I used to do regularly on my race cars. Precision braking is only possible when you have a high, firm pedal and that means freshly bled brakes. It makes street cars more fun to drive too.

If you rotate your tires or have some other reason to remove your wheels, that makes a perfect time to bleed your brakes. Or, when you think it's time to bleed your brakes, that is a chance to rotate your tires, you get the idea.

The process is not difficult, especially with one of those simple "one man" brake bleeding devices. Just continue the bleeding process until you see fresh fluid in order to flush the system but be absolutely sure to keep sufficient fluid in the resivoir so that you don't introduce any air in the system. No need to remove fluid from the resoviour with some fancy piece of equipment. Just keep moving it through the brake lines until you've removed all the old fluid. With the help of a second person, it can be done for the cost of the fluid alone. I use an inexpensive suction type bleeder at the brake caliper, but some owners use a pressure pot hooked up to the master cylinder; suit yourself. A dab of thick grease on the bleed nipple to help seal the hose is a good idea. Don't spill brake fluid on any painted surface.

Interestingly enough, high performance brake fluid boils at a higher temperature; therefore, it will be better for racing and track days. But the typical high performance brake fluid is more prone to absorb moisture, so unlike good engine oil, your expensive, high-temp brake fluid should be changed more frequently, not less.

I think that getting in touch with your car by performing simple servicing procedures is a good thing. Flushing brake fluid may not do anything for the short-term owner, but the guy who finds your $75,000 Cayman in a barn 60 years from now and restores it to an expensive gem will thank you when he discovers corrosion-free brake components.
 
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