Brake Fluid Comparison Chart

[DaveW]

Since the 2025 racing season has started, and some will be flushing their brake fluid, I thought it would be beneficial to re-post this link that I have found very useful:

https://www.lelandwest.com/brake-flu...ison-chart.cfm

[J Leonard]

How about Mercury? Boils at 674F and probably doesn't retain moisture.

[Robert J. Alder]

What a great resource! Many thanks for sharing.

But, can't help but ask, what does DOT have against the color blue?
"US DOT: 'cease and desist' due to blue color "

[DaveW]

How about Mercury? Boils at 674F and probably doesn't retain moisture.

Other than being EXTREMELY poisonous, likely having terrible lubricity, and being VERY heavy, not much wrong with it...

[DaveW]

What a great resource! Many thanks for sharing.

But, can't help but ask, what does DOT have against the color blue?
US DOT: 'cease and desist' due to blue color

I don't know, but it WAS great in seeing when one had completely flushed the system...

[Tim Minor]

Dave,would you share what fluid you use.Inquiring minds want to know
Thanks for posting

[DanW]

What a great resource! Many thanks for sharing.

But, can't help but ask, what does DOT have against the color blue?
"US DOT: 'cease and desist' due to blue color "

ATE (Continental) found the blue dye did not meet the DOT specifications for brake fluid color, so they pulled it from the US market.

[DaveW]

Dave,would you share what fluid you use.Inquiring minds want to know
Thanks for posting

I had been using Castrol DOT 4 (previously LMA), but last year I switched to Amsoil Dominator (DOT 4) as a reasonably priced upgrade and because Castrol DOT 4 seemed to be unavailable. The Amsoil fluid is not too expensive, and if you sign up for their Preferred Customer status, you get a significant discount and free shipping.

Amsoil is noted for their expertise in fluid properties, including lubricity, so based on that and opinions on ApexSpeed, I think their BF will treat our master cylinders, calipers, and slave cylinders well.

Link to thread on brake fluid: https://www.apexspeed.com/forums/sho...ht=brake+fluid

[Rick Iverson]

Dave:

Thank you for sharing.

[Rick Kirchner]

Interesting - the StopTech stuff looks pretty good!

[EYERACE]

I have liked AP551 for years and have a little stock of it laying around........so I hadn't shopped for it lately......thanks for the post as I now know it's called something new, and the label looks different too.......AP Radi-CAL R1.

Why the heck do companies change stuff that doesn't need changing? ....ah yes!......New Coke.

[patman]

Thanks for the chart.

I would just like to throw this out there for anyone new who might be reading this:

1) Price is relevant to how often you change it. SRF and some of the other high wet boiling point fluids can be run for a whole season, whereas cheaper fluids need to be flushed for each event. Full season cost is a lot lower overall and no need to hassle with it.

2) This data does not include 'feel'. Depending on your braking system, there can be significant difference in pedal feel between fluids. Some fluids, including really expensive ones, feel a little bit mushy even when perfectly bled. This may or may not be an issue for your style and setup. Shopping around different options is worth doing.

[stonebridge20]

I've got 120 quarts of GTLMA so I'm good for a while.

[kea]

I started using Cartel 570, DOT3 (570 dry boiling) back about 1980. We how use their 580, Dot 4. in 1/2 ltr container (not as listed in chart).

[DaveW]

I've got 120 quarts of GTLMA so I'm good for a while.

Quarts ??? That seems improbable. 12 oz bottles ?

[RussMcB]

<snip>

2) This data does not include 'feel'. Depending on your braking system, there can be significant difference in pedal feel between fluids. Some fluids, including really expensive ones, feel a little bit mushy even when perfectly bled. This may or may not be an issue for your style and setup. Shopping around different options is worth doing.

Interesting. I think a hard pedal is what we all strive for. Do you know how we can learn more about this characteristic? I've always assumed all brake fluid is not compressible (probably naively)

[DaveW]

Interesting hard pedal feel cause - I've never noticed any significant difference in brake fluid compressibility, but I have noticed a difference in brake pad stiffness. Some pad compounds I've tried apparently have lower stiffness (modulus) than others and make the pedal feel a bit soft.

Other things obviously affect pedal feel - flex in master cylinder mounting, brake balance setup, caliper stiffness, too soft brake lines, etc. can allow too much travel.

The Carbotech XP20's and Alcon calipers I am now using give a very stiff pedal feel.

[stonebridge20]

Quarts ??? That seems improbable. 12 oz bottles ?

Sorry Dave. Actually Liters, not quarts.

Yes, 120 of them.

*Trophys in the background for ego purposes only.

[DaveW]

Sorry Dave. Actually Liters, not quarts.

Yes, 120 of them.

*Trophys in the background for ego purposes only.

Well, you're never going to run out...

Nice trophy collection !!

[DaveW]

Interesting. I think a hard pedal is what we all strive for. Do you know how we can learn more about this characteristic? I've always assumed all brake fluid is not compressible (probably naively)

Everything is compressible - it's just a matter of how compressible it is. Fluids in general are considered essentially incompressible for simplicity in analyzing flow and other fluid analyses. In reality, there is nothing that is totally incompressible even though it can be so minor it can't be measured with normal tests.

From the web:
... fluids are not totally incompressible; while many liquids like water are often considered "incompressible" in everyday situations, technically all fluids experience some degree of compression when under pressure, meaning no fluid is truly incompressible; this concept is often used as an approximation for calculations where the change in volume due to pressure is very small.

[stonebridge20]

Well, you're never going to run out...

Nice trophy collection !!

We do a considerable amount of brake and clutch fluid flushes on all the British Sportscars that we service and repair.

[DaveW]

AFAIK, all brake fluid manufacturers (Amsoil, Castrol, etc.) and sellers advise to not use BF more than 2 years after its manufacturing date even if it's in an unopened container. IMO, that recommendation is, in most cases, especially if it's stored in reasonably dry conditions, a bit of overkill. Modern synthetic BF's are not nearly as hygroscopic as older organic BF's.

In the racecar I've used Castrol LMA (an early synthetic) that was likely stored for 10+ years, and had no issues doing that as long as it was in an unopened container.

So, just to be cautious, the bottom line is to not buy more BF than you are likely to use in the next few years. One exception might be BF in unopened metal cans which don't allow moisture into the fluid.

YMMV

[patman]

Interesting. I think a hard pedal is what we all strive for. Do you know how we can learn more about this characteristic? I've always assumed all brake fluid is not compressible (probably naively)

I am not aware of any public data about this. Brake fluid is not incompressible, it just has very low compressibility. Similarly there is also a viscosity element that probably contributes. I can tell you from personal testing that SRF will give a slightly softer pedal feel than RBF 660 for example. In a car with a booster, you can't tell at all really. In certain formula cars it is enough of a difference to influence fluid choice.

The design of the brake system plays a role obviously as well. Volume and pedal ratios, flexibility of the lines and calipers, compressibility of the pad all influence whether the fluid stiffness is relevant or not.

My point is really just that if one is not happy with performance of fluid, testing a couple other brands is worth doing even if the published specifications are the same- they don't always tell the whole story.

[Teuobk]

The bulk modulus of brake fluid is about 1.75 GPa. If we assume that you have a brake system with 8 ft of -3AN line, and the line doesn't expand at all, and your pedal ratio is 4:1, and your master cylinder bore size is 0.75", and your brake system pressure goes from 0 to 1000 psi, then the movement at your pedal due to the compression of the brake fluid due itself to that pressure change will be about 1/16".

I'm not entirely convinced that the various brake fluids will have different enough bulk moduli to have a material effect on the brake feel, but then, I can't find good data on exactly how much they vary.

My personal suspicion is that perceived pedal stiffness is far more sensitive to flex in the pedal and flex in the caliper than to compression of the brake fluid. This is especially true on monoblock calipers of poor design and/or floating calipers. If you ever want to freak yourself out, take a good look at how much the floating calipers flex on a street car between minimum and maximum braking pressure.

Jeff