What’s important when choosing brake fluid for a classic race car?

Well, it’s a discussion that pops up every now and then – especially near the paddock or the race track. Most of the time I tend not to participate in those discussions. But I want to share my perspective and some of the best products on the market today.
Of course, in a racing environment, a lot of parts have to work a lot harder, especially brakes. Higher speeds and much more intense presses on the brake pedal and as a result – much higher temperatures than with your daily commuting car. 
 
So make sure you install the right calipers, pads, discs and also – brake fluid that are all capable of withstanding those temperatures to avoid fading. Fading means losing performance once the temperatures are too high. You don’t want that, believe me, especially not with your track car.
 
Selecting the right brake fluid is not only vital but you might want to consider a few things:

What does the DOT rating mean?

Brake fluids are designed to meet industry standards, one of these standards which is most commonly used is the DOT rating (US Dep. of Transportation).

You might have seen ratings like DOT 3, DOT 4 and DOT 5. The higher the number, the better the performance of the brake fluid. 

DOT 3, DOT 4 and DOT 5.1 are glycol based brake fluids, can be used in the same system and can be mixed. However, if you mix, the temperature point will remain the one of the lowest DOT rated product in your system. Glycol based fluids will absorb moisture even the system is “closed”.

Means, if you need a higher temperature range, flush the system and use the one with the higher rating.

DOT 5 (not DOT 5.1) is silicone based and CAN’T be combined with glycol based types. Keep in mind, any traces of other brake fluids will ruin your braking performance. So it’s best if you had an complete overhaul with new hoses. Silicone based fluid will not absorb water, so you will have a more consistant feel, but it’s not compatible with ABS brake systems. We’re talking classic race cars here, but just wanted to mention that.

What does boiling point of brake fluids mean?

At some point you will come across two terms, dry boiling point and wet boiling point. Dry boiling point is the temperature when the fluid starts boiling before it had the chance to absorb water, wet boiling point is the temperature once water has been absorbed into the fluid.

Best brake fluids for classic race cars

Castrol React SRF

Most likely the most used brake fluid in motorsport, most Formula 1 teams use it. It has an excellent temperature performance, a high dry and wet boiling point which means it will not lose performance once it has absorbed water. 

Dry Boiling Point: 608°F (320°C), Wet Boiling Point: 518°F (270°C), DOT Rating: 3 and 4

Motul RBF 660

It’s the DOT 4 brake fluid with the highest dry boiling point which makes it superior to DOT 5 and DOT 5.1 brake fluids. Ideally suited to cars with all kinds of braking systems.
 
Dry Boiling Point: 617°F (325°C), Wet Boiling Point: 400°F (204°C), DOT Rating: 4

Maxima Racing DOT 5

Being a silicone brake fluid, it’s not affected by moisture intake and therefore it provides long lasting performance. More consistent brake pedal feel and the same boiling point. It will also not affect plastic or paintwork, but don’t mix it with glycol based brake fluid! If you want to replace your current brake fluid with DOT 5 silicon based brake fluid, flush your system completely!

Boiling Point: 572°F (300°C), DOT Rating: 5

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