Determining the Type of Fluid in your Kart Brake System Before Bleeding

Chassis Setup, Tires & Handling Forum
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Before you flush or add fluid to you brake system, it is essential that you add the same type of fluid to the system. It’s nothing to do with “racing” vs non racing, or anything else and everything to do with chemical composition.

  1. Glycol based (DOT 3, or 4)
  2. Silicone base ( DOT 5)
  3. Hybrid (mostly glycol) DOT 5.1

Do not mix types of fluid, as doing so will result in seal deterioration and possible brake failure.

To determine the type of fluid in your system:

  • Take a few drops of the brake fluid and put it in a small container.

  • Add a few drops of water and mix.

  • If the water mixes with the brake fluid, it is Glycol based. If the water does not mix with the brake fluid it is silicone based.

If you decide to switch from one to the other, the best practice is to change all seals and completely flush the system before refilling.

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5.1 is glycol based.

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Murky, it depends on the exact composition. It has to be less than 70% silicone. But I’d rather not take a chance personally.

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Paul E Martin Jr. Shared some good insights on Facebook about things to consider for vintage brake systems.

Let me provide a little history here concerning kart brake systems. Pretty much the first hydraulic brake system made for karts was the Hurst/Airheart system that most of we older guys used on our early karts from the '60’s.

H/A used two types of seals for their systems but karting nearly always got the Nitrile Buna-N seals that were compatible with the red mineral base brake fluid that was used in the aircraft industry. It is a relatively high boiling point fluid and suitable for karting.

When Enginetics came along in the late 70’s, they chose to use DOT-5 Silicone brake fluid. It’s main advantages over DOT 3,4 fluids was a higher boiling point and it is hydrophobic, meaning it does not absorb moisture and consequently reduce the boiling point of the fluid. DOT 3-4 fluid are hygroscopic meaning they absorb any moisture available to it. This is a bigger problem in humid areas of the country than dry areas. Think Florida versus Arizona.

Another advantage of silicone fluid is that it will not harm your finish on your kart, Harley or collectible car.

Glycol base fluids make pretty good paint remover. Silicone fluid can be used with any of the seals typically used in brake systems. It cannot be mixed with glycol based DOT 3,4 fluids.

You could not use DOT 3,4 brake fluid in H/A, Enginetics or MCP standard brake systems without changing to Ethylene Propylene (E-P) seals.

As mentioned earlier, you may use DOT-5 silicone fluid with Nitrile Buna or E=P seals with no problem. Just don’t add it to existing systems with glycol base fluids.

Silicone brake fluids one downside is that it will expand more than the glycol based fluids. Technically it is also more compressible but I personally have never been able to feel that difference.

Long story short, you have to use either mineral base or silicone fluid with H/A, Enginetics and MCP systems unless the seals have been changed from standard. Mineral base fluid is not compatible with E-P seals but DOT-5 silicone is. I hope this helps clear up this issue.

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Tagging for future reference.

So you can replace glycol fluids with silicone ones without seal changes, but not the other way. Interesting. I wonder what is in my kart ???

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Nice thread!

Keep it up KP.

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So, James, are you implying that DOT 5 can be used in a brake system that specifies DOT 4?

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No. DOT 5 is NOT the same as DOT 5.1.

Only DOT 5.1 is compatible with DOT 3 and DOT 4 systems.

Glycol-based (DOT 3, 4, 5.1)

Silicone-based (DOT 5)

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IF the system has been flushed and had all seals changed, yes. Of course it’s a personal preference in that case, vs manufacturer recommendation.

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Assuming you can find the correct seals for your brake system which use a silicone-compatible rubber.

Though, i’m not sure why you’d want to run a silicone-based fluid in a modern system. The boiling points of most glycol-based fluids is high enough to not have to worry about it.

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Actually, it’s new. As in, haven’t charged it yet. It’s actually the Energy Corse brake system, which looks like a “knock off” version of the CRG VEN05, & DOT 4 is the spec fluid.

But DOT 5 is okay to use?

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I think it was said further up the thread
DOT 3, Dot 4 and DOT 5.1 are compatible
DOT 5.0 is not.

I wouldn’t put DOT 5.1 fluid in a DOT 3,4,5.1 system

I’m in Australia, other world standards may be different.

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@Jacedownsouth

That’s why I’m seeking clarification.

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NO.

Unless you find the correct seals which are silicone compatible. But really, i’m not sure why you’d even consider DOT 5 - it’s not easy to find.

DO NOT MIX

DOT 5.1 =/= DOT 5

I have made this mistake before:

You CANNOT use DOT 5 in a DOT 3,4,5.1 system.

I have used DOT 5 fluid in a system designed for glycol-based fluids and I had to replace all the seals in my system as it failed within days - every seal in the system was softened, swelled, with most of them torn after a few days (of simply sitting) and one day of minimal use.

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@M_Martin,

This is how I have always understood it.

Is 5.1 compatible (with DOT 4), & does it offer any advantage?

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yes. I believe that’s been mentioned many times throughout this thread.

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So last night I experienced brake fade during my karting session. It was the first time out with a kart I bought. I suspect it has dot3 fluid.

Do you guys recommend me flushing the system and go for 5.1 (even though the cap states dot 3 or 4)?

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Brake fade is insanely rare, even with DOT3. Maybe it was contaminated?

My recommendation would be to go with a DOT4 “racing” fluid such as RBF600. Something that is compatible with non racing fluid.

I’d also check things over mechanically, ensuring that the axle isn’t sliding and that the pads are retracting.

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Thanks James. The axle was a little bent. I’ll change that, inspect everything mechanically and refresh the fluid with dot4.

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Just for informational purposes, as I was curious about the plusses and minuses of 5.1 vs RBF600.

“Compared to Motul’s DOT 5.1 brake fluid, RBF600 has higher dry and wet boiling points, but shorter lifespan . It is expected that RBF600 will need to be flushed about twice as frequently as DOT 5.1. Compared to Motul’s RBF660 brake fluid, RBF600 has a lower dry boiling point and a slightly higher wet boiling point.”

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