Brake Fluid Anti Corrosion

[Sam2000]

Seems that the anti corrosives in brake fluid are the most important feature for longevity.

In that case, could it be that the domestics generally don't have change intervals because their OEM brake fluids have more anti corrosives?

If not, is it arguable that OEM brake fluids are better because they will more precisely match the elements that need protecting in the braking system?

 

[Olas]

Some anti-corrosives, but its still hygroscopic and will still need changing..they used to say every two years, some now say every 5...unless you can find a hydrophobic brake fluid.there will always be a change.interval.... even with anti-corrosives.in place, steam is still very compressible and ice in the lines is a sure way to stop stopping.

Have you thought about buying a hydrometer and using the specific gravity of the fluid to determine how much life is.left in it?

 

[Turk]

Unfortunately, most people don't change their brake fluid, ever.

 

[AKhan87]

Originally Posted By: Turk
Unfortunately, most people don't change their brake fluid, ever.



That reminds me, just did a full brake fluid change in all three of my cars and used about a quart of brake fluid in each, no performance difference of any sort but in the 96 civic, the fluid was dirty black...now amber with the fresh fluid. I finally understand that it is a required fluid change.

 

[Turk]

Originally Posted By: 01_celica_gt
Originally Posted By: Turk
Unfortunately, most people don't change their brake fluid, ever.



That reminds me, just did a full brake fluid change in all three of my cars and used about a quart of brake fluid in each, no performance difference of any sort but in the 96 civic, the fluid was dirty black...now amber with the fresh fluid. I finally understand that it is a required fluid change.



Mine was original at 13 years old when I got my Saturn.

Flushed & filled with Amsoil DOT 3 and noticed zero difference. The difference will come when everything's all heated up and you have to stop hard. The new fluid won't give out.

 

[JHZR2]

Originally Posted By: Turk
Unfortunately, most people don't change their brake fluid, ever.



That's the interesting aspect to it... They dont, and how many actually have issues from frozen, corroded or steam-filled brake lines? May be too late when you find out, and fortunately, if/when pads are done, generally the worst part of the fluid gets flushed out anyway as the piston is compressed.

Ive seen "LMA" fluids (low moisture absorption), and also have heard that DOT3 fluids take up moisture at a slower rate than 4, but I dont know that there is data for any of this...

 

[mene]

Originally Posted By: 01_celica_gt
Originally Posted By: Turk
Unfortunately, most people don't change their brake fluid, ever.



That reminds me, just did a full brake fluid change in all three of my cars and used about a quart of brake fluid in each, no performance difference of any sort but in the 96 civic, the fluid was dirty black...now amber with the fresh fluid. I finally understand that it is a required fluid change.


How did it go? What fluid did you use? What method for the bleeding?

 

[mene]

Originally Posted By: Turk
Originally Posted By: 01_celica_gt
Originally Posted By: Turk
Unfortunately, most people don't change their brake fluid, ever.



That reminds me, just did a full brake fluid change in all three of my cars and used about a quart of brake fluid in each, no performance difference of any sort but in the 96 civic, the fluid was dirty black...now amber with the fresh fluid. I finally understand that it is a required fluid change.



Mine was original at 13 years old when I got my Saturn.

Flushed & filled with Amsoil DOT 3 and noticed zero difference. The difference will come when everything's all heated up and you have to stop hard. The new fluid won't give out.

The difference will also come from parts that don't wear out or very little, you will see how much longer your MC, calipers and/or wheel cylinders will last, brake fluid have seal conditioners that keep them plyable and flexible reducing tears and cracks and helping seal better, besides that, when you bleed you remove most of the debris that damage the seals. Now be advise that "2 years", "3 years" is an average of the time to bleed, if you live in a hot and humid area you should bleed more often, in a dry and cold environment less often.

 

[MolaKule]

Originally Posted By: Sam2000
Seems that the anti corrosives in brake fluid are the most important feature for longevity.



All brake fluids have anti- rust/corrosion agents.

The total formulation is the important criteria.


As others have stated, brake fluid is hygroscopic and therefore, the brake system needs 'complete' flushing every two to three years.

Chemistry of Brake Fluids

 

[Ken2]

Quote:
Ive seen "LMA" fluids (low moisture absorption), and also have heard that DOT3 fluids take up moisture at a slower rate than 4, but I dont know that there is data for any of this...
The LMA might be more advertizing hype than a significant difference.

Yes, it is established that the borate esters that make the fluid qualify for DOT4 also cause the fluid to absorb moisture at a faster rate.

 

[Sam2000]

Originally Posted By: Olas
Some anti-corrosives, but its still hygroscopic and will still need changing..they used to say every two years, some now say every 5...unless you can find a hydrophobic brake fluid.there will always be a change.interval.... even with anti-corrosives.in place, steam is still very compressible and ice in the lines is a sure way to stop stopping.

Have you thought about buying a hydrometer and using the specific gravity of the fluid to determine how much life is.left in it?


I have copper test strips so I can test when the anti corrosives have worn out. This is better than testing for moisture.

You have a good point that all brake fluids will take on moisture. But some have very high wet braking temperatures so will theoretically be safer at 2 years than others.

So the decision point about flushing is corrosion.

It's obviously not going to be productive or quick actually testing different brands to figure out which has the longest lasting anti corrosives. That's why I was asking about this point specifically.

I suppose I could switch to LMA / high wet boiling point brake fluid as that is most likely going to last longer but who really knows?

 

[Sam2000]

Originally Posted By: MolaKule
Originally Posted By: Sam2000
Seems that the anti corrosives in brake fluid are the most important feature for longevity.



All brake fluids have anti- rust/corrosion agents.

The total formulation is the important criteria.


As others have stated, brake fluid is hygroscopic and therefore, the brake system needs 'complete' flushing every two to three years.

Chemistry of Brake Fluids


Thanks Molakule.

So have you seen any brands / formulations that last longer than others? Motul say their 5.1 is long life.

 

[HTSS_TR]

Originally Posted By: Turk
Unfortunately, most people don't change their brake fluid, ever.

So true.

When I had my car(s) at the local garage for some services I saw many older high performance cars such as BMW, Audi, MB ... have black fluid in the brake reservoir. The best time to bleed the brake is when they replace the pads, but the owners were not interest in paying for bleeding the brake.

 

[MolaKule]

Originally Posted By: Sam2000


Thanks Molakule.

So have you seen any brands / formulations that last longer than others? Motul say their 5.1 is long life.


Long life compared to what?

Motul has good fluids but most of the "Long Life" phrasing by them or anyone else is mostly marketing.

 

[willbur]

Interesting advice. Ford engineers visited junk yards, took brake fluid samples and found little adsorbed water in the samples. Perhaps this is the reason they do not require flushes? This may have changed since I first researched this topic. AFAIK, it's not water but copper leaching from the metal lines that's doing the corrosion. I would think this drops off after the copper stops leaching.