Changing break fluid

[lxskllr]

I've never changed brake fluid aside from incidental additions during brake work. While it may not be terribly expensive, it isn't free either. I'd find more fun ways of spending the money.

 

[OverVolt]

Do these fun ways of spending your money include not being smeared on the road when your brakes fail or...?

 

[master_shake_]

Do these fun ways of spending your money include not being smeared on the road when your brakes fail or...?

There isn't a roll eyes big enough for this stupid statement.

 

[Midwayman]

There isn't a roll eyes big enough for this stupid statement.

Not really. Brake fluid is one of those things that might be fine in 99% of your driving, but can suddenly fail in an emergency situation. Stupid not to change it once in awhile, especially given how cheap it is.

 

[razel]

Lots of truths. The most important ones.

- You did find a good mechanic who refused to take your money even though you wanted to give.
- There's nothing permanent, brake fluid loves water and breaks down however most of us do not even come close to stressing our brake system's capabilities. It is the most important safety feature in your car and like many safety features they are designed for double the expected stresses.

Therefore like transmission fluid, most of us don't touch it since it's often too late and chances are if the driver suspects something wrong, the mechanic knows something is wrong and wants to avoid being the blame that since they touched it, they broke it.

You can change some of it yourself by just turkey bastering the reservoir. It's usually less than 8oz since there's often a stopper and most brake fluid you buy is 16oz or more. You don't want to use very old opened up brake fluid either, so might as well repeat it again after a few months to use it all up.

There is little circulation in the brake system so all you are really doing is diluting the top. If you want to change all of it you'll have to bleed the breaks. Bleeding breaks is not more difficult than changing oil. It's just much dirtier and messier.

 

[bigi]

Lots of truths. The most important ones.

...
Bleeding breaks is not more difficult than changing oil. It's just much dirtier and messier.

Not really.

One does not have to be air tight with oil. With brake fluid however, once air gets in, you need to re-flush until all of the air is out.
Also, with some cars bleeding order is important in order not to introduce dirty fluid back into system.

In my book, those are very different level of difficulty.

 

[dtgoodwin]

razel hits it right on the head. Don't mess with your brakes. I'll add that I've had two experiences with bad fluid. My parents owned an '86 Pontiac 6000 STE with ABS. Instead of having an on-demand pump when ABS kicks in and needs to bleed off pressure and reapply, their car had a pump and pressure reservoir that provided power assist. After a few years on hot days the fluid would boil in the system (I didn't know it then), and the pump would run continuously because it couldn't build pressure and can't pump air.

Second example is in my own car - a Prius. It too, uses a pump and stored pressure to provide power assist. Of course, it's a far more complex braking system than others because depending upon pressure applied, speed, and state of charge of the hybrid battery, the friction brakes may not even be involved in braking events. Anyway, when we bought the car used with 130K miles, it hadn't had the fluid changed in a while, or maybe even ever. When stopped, the brake controller would make a well known "barking" sound occasionally. After 6 months or so, the pump was unable to build pressure. I flushed the system, and it did not resolve either problem. I replaced the controller and could see all sorts of corrosion of the aluminum just inside where the lines attach. I didn't open it up, but it was pretty clear that the failure was caused, or at least aggravated by water in the fluid. Let's just say that it was not an inexpensive part. List price new is around 3K. I'm glad to have found one in excellent condition from a wrecking yard for $150.

I bought a brake system specific vacuum assisted vacuum pump from Harbor Freight. It comes with a bottle to keep the reservoir full as fluid is removed. It seems one of those rare things from Harbor Freight that actually work well. I'll never go back to the manual method.

 

[Pacfanweb]

I replaced the fluid in my 2000 Insight's brake lines at about 200k, at the same time as I replaced the clutch master. It was pretty dark, but the brakes didn't feel any different afterward.

If the system was already operating properly, they shouldn't feel any different after merely changing the fluid.

It's done to prevent having problems caused by dirty, contaminated fluid.....but dirty, contaminated brake fluid still functions just as well as brand new clean fluid.

 

[JCH13]

If the system was already operating properly, they shouldn't feel any different after merely changing the fluid.

It's done to prevent having problems caused by dirty, contaminated fluid.....but dirty, contaminated brake fluid still functions just as well as brand new clean fluid.

Please explain how dirty, contaminated, fluid can cause problems but also functions just as well as brand-new clean fluid. I'm especially interested to hear how you figure that the boiling temperature of dirty fluid is the same as clean fluid.

 

[Railgun]

..

You can change some of it yourself by just turkey bastering the reservoir.

There is little circulation in the brake system so all you are really doing is diluting the top.

Yeah. So no basting. What a terrible recommendation.

 

[T2urtle]

I try to do this every brake job i perform, assuming the bleeders open. Being in the salt belt, not many open.

I've seen many cars never do then and work perfectly fine. 300k cars from early 199x. No issues with brakes, no spongy pedal or anything. Fluid blacker then oil.

 

[master_shake_]

Not really. Brake fluid is one of those things that might be fine in 99% of your driving, but can suddenly fail in an emergency situation. Stupid not to change it once in awhile, especially given how cheap it is.

how exactly can brake fluid fail?

besides a burst component.

 

[razel]

Yeah. So no basting. What a terrible recommendation.

What's more terrible is that you don't contribute. How exactly do your 3 sentences help us?

 

[bruceb]

My car lived and was driven since new till Jan 2016 in New Jersey with all it's road salt. When my brake rear hard line failed down here in NC (about a month ago) I was also worried that the shop might have trouble with the bleeder screws. Apparently they did not and were able to replace the pipe, brake fluid and bleed the system. (I was lucky we were approaching a stop sign on a bit of an uphill and not going fast when the brakes quit)

 

[Railgun]

How exactly do your 3 sentences help us?

It helps a helluva lot more than your post does.

 

[Pacfanweb]

Please explain how dirty, contaminated, fluid can cause problems but also functions just as well as brand-new clean fluid. I'm especially interested to hear how you figure that the boiling temperature of dirty fluid is the same as clean fluid.

It's really pretty easy to figure out if you understand the subject matter.

As I stated originally, "IF THE SYSTEM WAS ALREADY OPERATING PROPERLY" you should not feel any difference after you change it.

Changing brake fluid, or more accurately, the REASON for changing it is no different than changing oil. The interval is a lot longer, but the reason you change it is the same: To prevent failure if the fluid gets too dirty/contaminated to do its job.

Is old brake fluid at the end of its designed operating life as "good" as new? Of course not. It's old and it's dirty.

But is it still doing its job? Damn right it is. That's because it's DESIGNED to still be effective even while somewhat dirty.

Same as motor oil. Is motor oil at the end of its 5,000 mile interval as good as it was when it was new?
No, of course not. Is it still lubing your engine properly and within the manufacturer's designed specs? Yep, sure is.

But....it's about to NOT be doing that. Just like the brake fluid is, just like trans fluid, coolant, diff lube, etc, if you run them over the manufacturer's recommended interval. But within the interval? It's working perfectly fine, dirty or not.

 

[Zivic]

I've never done this before....but why wouldn't you just pop the lid on the master cylinder and siphon out what you can with a syringe pump....then top it back off to the line with fresh fluid....This wouldn't clear the fluid in the lines, but I would think replacing 70% or so from the reservoir would be far quicker, easier, and almost as effective.

this doesn't touch the fluid in the lines or calipers. the fluid in the lines and calipers just sits there yr after yr. it isn't like the coolant or oil where it is constantly cycled.

I change the brake fluid on my cars every 3-5 yrs

 

[jlee]

how exactly can brake fluid fail?

besides a burst component.

The boiling point of dry (new) fluid is substantially higher than that of wet (has absorbed water) fluid.

I haven't fact-checked this but I have no reason to doubt wikipedia's accuracy on the topic:

Dry boiling point	Wet boiling point
DOT 3	205 °C (401 °F)	140 °C (284 °F)
DOT 4	230 °C (446 °F)	155 °C (311 °F)
LHM+	249 °C (480 °F)	249 °C (480 °F)
DOT 5	260 °C (500 °F)	180 °C (356 °F)

More info.

If the boiling point of the brake fluid has dropped to too low a value due to high water content, there will be a risk of vapour locks forming in the brake system. The compression of these vapour locks can lead to the total failure of the brake system. The brake pedal can be pressed right down to the floor but the vehicle brakes will not be applied. With safety in mind, for this reason it is of vital importance to have the brake fluid tested annually and changed at the prescribed intervals. The brake lines and brake hoses should also be inspected as part of this check and replaced in the event of damage.

tldr; The older your brake fluid is, the lower its boiling point. If your brake fluid boils, you're going to have a bad day.

 

[jlee]

It's really pretty easy to figure out if you understand the subject matter.

As I stated originally, "IF THE SYSTEM WAS ALREADY OPERATING PROPERLY" you should not feel any difference after you change it.

Changing brake fluid, or more accurately, the REASON for changing it is no different than changing oil. The interval is a lot longer, but the reason you change it is the same: To prevent failure if the fluid gets too dirty/contaminated to do its job.

Is old brake fluid at the end of its designed operating life as "good" as new? Of course not. It's old and it's dirty.

But is it still doing its job? Damn right it is. That's because it's DESIGNED to still be effective even while somewhat dirty.

Same as motor oil. Is motor oil at the end of its 5,000 mile interval as good as it was when it was new?
No, of course not. Is it still lubing your engine properly and within the manufacturer's designed specs? Yep, sure is.

But....it's about to NOT be doing that. Just like the brake fluid is, just like trans fluid, coolant, diff lube, etc, if you run them over the manufacturer's recommended interval. But within the interval? It's working perfectly fine, dirty or not.

I can see the abstract analogy you're taking by comparing brake fluid to oil, but that is a faulty comparison. Brake fluid needs to be changed periodically because it is hygroscopic by design. As the water content of brake fluid increases, its boiling point decreases. Once the boiling point has dropped to the operating temperature of the brake fluid, it will boil and cause brake failure. It has nothing to do with being old or dirty. A brake system that "WAS ALREADY OPERATING PROPERLY" can suddenly be no longer operating properly if you have a heavy braking event and you boil your fluid.

Coolant is another topic entirely - anti-corrosion and anti-freeze properties/etc aside, plain water will cool an engine just fine.

 

[master_shake_]

The boiling point of dry (new) fluid is substantially higher than that of wet (has absorbed water) fluid.

I haven't fact-checked this but I have no reason to doubt wikipedia's accuracy on the topic:

Dry boiling point    Wet boiling point
DOT 3    205 °C (401 °F)    140 °C (284 °F)
DOT 4    230 °C (446 °F)    155 °C (311 °F)
LHM+    249 °C (480 °F)    249 °C (480 °F)
DOT 5    260 °C (500 °F)    180 °C (356 °F)

tldr; The older your brake fluid is, the lower its boiling point. If your brake fluid boils, you're going to have a bad day.

yeah i could totally see that happening....

in nascar.

everyday driving even in an emergency stop? NOPE!

well unless you really like double footing to the extent that you are literally brake torquing everywhere.

 

[jlee]

yeah i could totally see that happening....

in nascar.

everyday driving even in an emergency stop? NOPE!

well unless you really like double footing to the extent you are literally brake torquing everywhere.

I've had brake rotors glow on a street car. Use an IR thermometer and check your brake temperatures after you've been driving for a while - you may be surprised at how hot they get.

Obviously this is far more likely in track conditions due to the constant braking - stuff like this can happen.

 

[Jimzz]

yeah i could totally see that happening....

in nascar.

everyday driving even in an emergency stop? NOPE!

well unless you really like double footing to the extent that you are literally brake torquing everywhere.

Trucks can boil their brake fluid when towing; esp in hill/mountain areas, old brake fluid, and bad braking/driving habits.

Corrosion is another issue street cars do have, esp ABS ones. Hyundai had to recall some of its cars as the brake fluid was not protecting the brake system and caused some accidents and brake failure. So I think all early Genesis sedans got a brake flush with Dot4 fluid to fix it.

 

[Pacfanweb]

I can see the abstract analogy you're taking by comparing brake fluid to oil, but that is a faulty comparison. Brake fluid needs to be changed periodically because it is hygroscopic by design. As the water content of brake fluid increases, its boiling point decreases. Once the boiling point has dropped to the operating temperature of the brake fluid, it will boil and cause brake failure. It has nothing to do with being old or dirty. A brake system that "WAS ALREADY OPERATING PROPERLY" can suddenly be no longer operating properly if you have a heavy braking event and you boil your fluid.

Coolant is another topic entirely - anti-corrosion and anti-freeze properties/etc aside, plain water will cool an engine just fine.

I know brake fluid is hygroscopic. Point was, brake fluid is designed to withstand being contaminated up to a certain point....just like oil is.

So if you're not "to that point" where your manufacturer recommends you change the fluid....then while yes, it's dirty...it still works fine. And when you change it, you're not going to *feel* the slightest difference. It just won't be as dirty and that far along towards the "it's too contaminated" point.

And dirt absolutely makes a difference. Ask your stuck calipers or wheel cylinders or you failed master cylinder or ABS pump how they like that nasty fluid. Water in the fluid can also hurt these parts.

 

[Pacfanweb]

I've had brake rotors glow on a street car. Use an IR thermometer and check your brake temperatures after you've been driving for a while - you may be surprised at how hot they get.

Obviously this is far more likely in track conditions due to the constant braking - stuff like this can happen.

If you were driving the piss out of it, maybe. There's no car anywhere that has its rotors get red-hot in normal driving conditions.

The advice given that you responded to clearly isn't directed towards hot rodders and enthusiasts, but your average daily driver.

 

[jlee]

If you were driving the piss out of it, maybe. There's no car anywhere that has its rotors get red-hot in normal driving conditions.

The advice given that you responded to clearly isn't directed towards hot rodders and enthusiasts, but your average daily driver.

"Maybe" here's a picture of someone lighting a cigarette off of it. I didn't say "normal driving conditions" - I said "street car." If you're going to argue with people, argue statements that were made instead of shit you make up.