There are two very different types of brake fluid used in bicycles today, and they are not interchangeable. The manufacturers build brakes to accept either DOT-rated fluid or mineral oil, but never both, so you must replace your brake fluid with the same kind of fluid.
Otherwise, your brakes won’t work right. Can you use car brake fluid on a mountain bike?
You can use car brake fluid in a mountain bike with brakes that use DOT 5.1 or 4 but not in place of mineral oil. DOT-rated brake fluid can use DOT car brake fluid when they’re compatible. A DOT rating indicates the boiling point and viscosity, and a thicker or thinner fluid won’t work the same way.
To see all of my up-to-date recommendations for bikes and cycling gear, check out this resource that I made for you!
Can I Use Car Brake Fluid On My MTB
Before you ask if you can use car brake fluid on your MTB, you should first ask what kind of brakes it has.
For example, Shimano is an incredibly popular parts maker that produces brakes on many bikes uses only proprietary mineral oil.
As a result of that manufacturing decision, you cannot use car brake fluid in Shimano brakes.
The brakes typically indicate if they have a DOT rating on the outside. It will say DOT 4 or 5.1. Only brakes with a DOT 4 or 5.1 are compatible with DOT 4 car brake fluid.
You can buy the bike-specific brake fluid, but the compatible DOT 4 car version is less expensive and equally effective.
Is Car And Bike Brake Fluid The Same
Car brake fluid usually comes in three different DOT ratings. However, only one of these car brake fluids is the same as your mountain bike. You will only need number four as long as you ride a mountain bike.
According to Auto How Stuff Works, “The three main types of brake fluid now available are DOT3, DOT4, and DOT5. DOT3 and DOT4 are glycol-based fluids, and DOT5 is silicon-based. The main difference is that DOT3 and DOT4 absorb water, while DOT5 doesn’t. “
What Brake Fluid Do I Need For My Mountain Bike
You will either need mineral oil or DOT 5.1 fluid for your bicycle. However, DOT 4 is cross-compatible with 5.1.
As for the mineral oil, Shimano brakes use a proprietary brake fluid that is made of mineral oil, so you have to use the Shimano brand of oil.
In fact, it’s best always to check your user manual or the manufacture of your brakes and only use the same type of brake fluid they recommend.
How To Use Car Brake Fluid In A Mountain Bike
Using car brake fluid in a mountain bike is very simple. Once you’ve determined your hydraulic disc brakes, require DOT 4 or compatible DOT 5.1, all you need to do is go to the nearest auto supply shop or order a bottle of DOT 4 online.
Below are the steps for bleeding your bike brakes:
- Put your bike on a stand.
- Use a 4mm Allen key to raise the brake levers until they’re parallel to the ground. Then tighten so they remain in this position.
- Remove the wheel.
- Next, remove the cotter pin. Please note that you may have to do this on both wheels, but I’m not listing it twice since you repeat the process exactly.
- Use a 3mm Allen key to remove the bolt that secures the brake pads in place. Keep these away from the rest of the process to avoid contaminating them with oil.
- Press out the caliper pistons with a tire lever.
- Put your bleed block into the brake caliper and secure it tightly.
- Then put the bleed cup on the brake lever.
- Attach your rubber oil line and catch bottle.
- Open both sides, caliper, and lever, and let oil flow in until you see some clean oil enter the catch bottle.
- Finally, you close the bleed port and clean up. Remember to reinstall those brake pads.
If this is your first time changing the fluid in your mountain bike brakes, or it’s been a long time, I strongly recommend watching this video on how to bleed any bicycles’ brake fluid.
Berm Peak shows you how simple it is and why this intimidating task is easier than you’d expect.
Mountain Bike Brake Bleed Kit
You can’t just pour in brake fluid like you’d add water or oil to your car. You’re going to need special tools to bleed the old fluid off from your brakes and add new, fresh fluid again when you’re done.
One of the most popular and common brands that manufacture disc brakes for mountain bikes to use DOT fluid is SRAM, and luckily they make a kit specific to their brakes.
SRAM makes a lot of different brakes, but the SRAM Standard Disc Brake Bleed Kit from Amazon works on all of them.
You get all the tools you need to bleed your SRAM MTB brakes like compression ferrules, barbed tubing inserts, and bleed syringes with clamp tubes and fittings for both threaded bleed ports and Bleeding Edge bleed ports.
Better still, you also get an instruction manual to help you do the job.
The SRAM Standard Disc Brake Bleed Kit also comes with 5.1 fluid to help you get back to riding faster. Plus, all the parts are quality assured. To get your SRAM kit, click right here.
- Drip-free bleeding kit for hydraulic SRAM disc brakes
- With DOT5.1 brake fluid
- Each 1 bleed blocks for all Guide, XX and X0 brakes
Helpful Tips To Know About Using Car Brake Fluid In A Mountain Bike
Changing your own brake fluid is a skill every mountain bike rider needs because you never know when you might have to do this on the fly.
After all, brakes are vital for most forms of cycling, except some BMX, but having no brakes on a mountain could be especially disastrous.
Here are more helpful tips to know about using car brake fluid in a mountain bike.
- DOT 4 brake fluid can absorb water from the air around it. Always promptly cap your brake fluid bottle as soon as you have what you need out of it, and make sure to dispose of old bottles or those with broken caps properly.
- Ensure that there is no air in the brake system. If you let a pocket of air inside, it can interfere with the way your brakes function, causing damage and even potentially making the brakes fail. Proper brake fluid changes help prevent crashes, injuries, and damage to your bike.
- Be careful when handling DO 4 brake fluid. You should always wear gloves, but you also need to watch your paint job since this type of brake fluid can eat through paint.
- Learning to bleed your brake fluid is an essential skill. However, so is being prepared for what can happen before you suddenly realize you need new brake fluid. If you ride a mountain bike, please learn to bleed speed and crash properly. Hopefully, you will never find out the bad way that your brakes need fluid, but just in case you do, learning to stop safely in an emergency could save your life.
Some mountain bikes can use car brake fluid. Knowing what type of brakes your mountain bike has to determine what brake fluid to use is vital.
The popular brand Shimano only makes brakes that use mineral oil, which you cannot refill with car brake fluid.
However, other brands like SRAM use a DOT 5.1 fluid, which is compatible with DOT 4 car brake fluid. Always replace your brake fluid with the same style for a safe ride.