Would changing brake fluid and bleeding help stopping power?

[moribundman]

I can relate brake fading to not changing the brake fluid on a regular basis. Whether or not in phenomic's case it's due to bad brakes (and he did say the brakes were bad to begin with!), and not all cars have good brakes, a matter of his rotors being wet (did he pulse the brakes during the storm on occasion?), or whether there is some other problem with the brakes, is unclear. Just like it makes sense to check the whole brake system, it's a good idea to also change the brake fluid.

The 3 big US car makers do not recommend brake fluid change as part of preventive maintenance. They say that even 3% water in the brake fluid are acceptable and that this saturation is unlikely to occur in a sealed system. Fine. They don't have to stop the car from 130 mph.

I don't know of any European carmaker (including the Euro branches of Ford and GM) who do not specify a brake fluid change interval. 2 years seems to be the most common interval.

In my opinion, the brake fluid should contain a coloring agent that indicates when the fluid is overly saturated.

By the way, that DOT 5 silicone brake fluid that some cars use, results in a pretty lousy pedal feel. Unlike conventional brake fluid, the silicone fluid is compressable, resulting in a spongy brake feel. Maybe it won't be an issue in cars with a brake-by-wire system that can compensate for sponginess.

 

[labman]

quote:

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Originally posted by moribundman:
I can relate brake fading to not changing the brake fluid on a regular basis. snip....

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Please do so.

 

[moribundman]

I will.

http://www.google.com/search?q=brak...eid=firefox&start=0&start=0&ie=utf-8&oe=utf-8

 

[labman]

What a load of garbage. Brake fade is when the friction material gets hot enough to no longer provide friction. The fact that some people are misusing the term means they don't know what they are talking about. LOSS OF PEDAL IS NOT BRAKE FADE.

 

[Ray Garlington]

Labman, are you playing some sort of word game with everyone? ('common' brake problems, 'brake fade' definition, 'loss of pedal'...)

I'll respond to one of your semantic game questions, even though you answered it yourself:

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What I don't get is why so many of you are insisting you must change the brake fluid when none of you can relate it to preventing common brake problems. Yes, yes, yes, brake fluid is hygroscopic. Does that cause problems? Seldom.

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Brake fluid absorbs water, which in turn reduces its boiling point. Yes, this seldom causes problems, but when it does, the problem can be a complete loss of braking power. Doesn't that count as a 'common brake problem"? Perhaps not, because:

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LOSS OF PEDAL IS NOT BRAKE FADE.

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I guess "brake fade" == common problem not affected by brake fluid condition

and "loss of pedal" == problem affected by brake fluid condition, but doesn't count because it isn't 'common'

One last point: most 'authorities' (european auto makers in general) say the increased viscosity and mosture content of contaminated brake fluid increases wear and corrosion in abs systems. I'm guessing that doesn't count either for some reason.

 

[moribundman]

I love semantics. Let's call it "vapor fade" in case of boiling brake fluid.

 

[Ken2]

quote:

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Originally posted by moribundman:
that DOT 5 silicone brake fluid that some cars use, results in a pretty lousy pedal feel. Unlike conventional brake fluid, the silicone fluid is compressable, resulting in a spongy brake feel. Maybe it won't be an issue in cars with a brake-by-wire system that can compensate for sponginess.

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Isn't everything compressible to some degree...even a diamond? Anyway, silicone DOT5 brake fluid is about twice as compressible as conventional brake fluid. This is also one of the reasons why DOT5 is unsuitable for ABS systems.


Ken

 

[kevm14]

Also doesn't DOT5 not absorb water? I think that alone would mean death to an ABS system (because absorbing it is at least better than letting it sit around in pure form). Or maybe I'm way off...

 

[MaximaGuy]

The way I did it was using Valvoline Syn Dot3/4 Brake Fluid (starts off at 525F which is pretty good enough) ---

1) Get almost all the fluid off the master cylinder using some suction syrindge and then refill it with fresh fluid.
2) Start bleeding from the farthest tire from the master and do it 5 times. This should bring the old brake fluid from the lines out. After each side is done, refill the master to avoid running out of brake fluid..
3)Done and I did see my braking performance improve -- but more than than I don't see my master fluid boiling right after a long 300 mile drive.....

Enjoy.

 

[moribundman]

http://www.mg-sportcars.co.uk/Brake_Fluidsl_FA_Questions.htm

 

[labman]

Changing brake fluid is nearly useless. NONE, NONE of the posts here have given any facts suggesting boiling the brake fluid is likely to happen, although it is possible. It does nothing to prevent problems that do happen.

 

[Clement]

1994 Mercury Sable, 3.0L, about 117K miles (with that dammed axod metric transmission). My father took it for a drive one day, and the brake pedal went almost to the floor! Fearing the worst, I decided that it wouldn't hurt to bleed the brakes as it was probabally never done. Lo and behold there was air in the calipers! Now the brakes are rocl solid.

Bleeding helped.

 

[moribundman]

labman wrote:

quote:

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Changing brake fluid is nearly useless. NONE, NONE of the posts here have given any facts suggesting boiling the brake fluid is likely to happen, although it is possible. It does nothing to prevent problems that do happen.

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labman, what's the boiling point of water? How hot does brake fluid get under extreme conditions, which USUALLY DO OCCUR WHEN YOU NEED THE BRAKES THE MOST? What happens when the water in the brake fluid starts boiling? Oh yeah, you called it astutely "pedal loss." Like it falls off?

 

[MaximaGuy]

labman wrote:
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Changing brake fluid is nearly useless. NONE, NONE of the posts here have given any facts suggesting boiling the brake fluid is likely to happen, although it is possible. It does nothing to prevent problems that do happen.
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I can speak for myself though -- I did see my stock fluid boil and if it wasn't the cylinder cap, it would have been all over the place. Anyway, it is nice to do the bleeding atleast every 60K miles -- more a peace of mind that when one brakes it does work. I would continue to do it since it is a 1hrs job...

 

[Virtuoso]

Perhaps flushing the brake system with new fluid dosen't do as much good as say, a coolant flush.

But I know the fluid that came out (especially from the rear brakes) of my Taurus was pretty dark compared to what I was putting in. I'm glad I changed it out.

 

[tdi-rick]

quote:

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Changing brake fluid is nearly useless. NONE, NONE of the posts here have given any facts suggesting boiling the brake fluid is likely to happen, although it is possible. It does nothing to prevent problems that do happen.

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Labman, I have seen road cars 'boil' their OEM fluid at the track doing lap dashes and super sprints.
The only reliable, readily available fluid that would alleviate this was SRF.
As I pointed out earlier, all real race cars brake systems are regularly flushed. When using something like SRF that costs over A$100/litre retail, it isn't done just for fun.

As we have established in this thread, brake 'fade' is the phenomenom where the friction materials maximum operating temperature is exceeded, and its coefficient of friction starts to rapidly fall away.
This is characterised by a normal pedal height, but increasing pedal pressure for the same amount of retardation. It can lead to a total loss of braking power, and an awful smell from the brakes and your pants.

If too much of this heat passes through the backing plate, piston and into the fluid, it can create small amounts of vapourisation or boiling of the fluid in this region.
This is characterised by a loss of pedal height with a spongy feel to the pedal. This isn't to be confused with 'pad knockoff' where the pistons can retract slightly in opposed piston calipers, creating a slight loss of pedal height, however the feel of the pedal remains the same, and a slight tap or pump to the pedal returns it to its normal height.

In my trusty old Land Rover Defender I have Ferodo 4WD pads, which are either 600*c or 650*C rated. Testing these coming down a dirt mountain pass the other day, I had pretty severe pad fade by the bottom. I wsn't going terribly hard, as this road is sometimes used by logging trucks, and I wasn't fully loaded or towing.

Now I didn't use any temp tabs or paint on the discs, so I have to believe Federal Mogul/Ferodo that I exceeded 600*C. I have nice, fresh Castrol Response Super Dot 4 fluid in the system, a 284*C dry, 184*C wet fluid.

The pedal height didn't change, but generating those sort of braking temperatures, can anyone guess what the pedal would have felt like if I had 15 year old Dot 3 fluid in there ? (OK, the truck's only 5, but you get my point).

BTW, it always amazes me the amount of crap that is expelled in a full fluid flush. Discoloured fluid, almost microscopic metal filings (shine a light from behind the tube), etc.

Rick.

 

[XS650]

quote:

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Originally posted by kevm14:
Also doesn't DOT5 not absorb water? I think that alone would mean death to an ABS system (because absorbing it is at least better than letting it sit around in pure form). Or maybe I'm way off...

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You are correct. I was one of the early users of DOT 5 brake fluid in the late 1960s. It's lighter than water, so water separates out into globules of water that sit in the bottoms of you wheel and master cylindrs.

At least the corrosion is all on one side of the cylinder

It's better to have the moisture in solution so it isn't as concentrated and gets removed when you bleed/flush the brake system.