Motorcycle Brakes Won’t Bleed? 4 Reasons (Explained)

Bleeding the brakes can be a piece of cake, but what happens if they won’t bleed out? It’s essential to the brake system that the brake line be cleaned of dirty old fluid and maintain the brake pressure. If either of those things isn’t taken care of, brake system failure is imminent!         

We are going to take a look at the reasons your motorcycle brakes won’t bleed and give you an explanation as to why your afternoon’s project just got a little more time-consuming.

It’s a bummer, but you’ve come to the right place, muchachos! We’re going to give you the rundown of a few reasons your brakes might not be bleeding correctly when they should be. Hopefully, this will allow you to troubleshoot your braking system problems and correct the issue.

Here’s the short answer to why motorcycle brakes won’t bleed:

A motorcycle’s brake may fail to bleed if the brake fluid is contaminated with dirt or debris. Corrosion, blocked lines, and leaks can also prevent you from bleeding your brakes. Failure to fill the brake fluid reservoir and presence of air in the lines can also cause this problem.

A Few Common Reasons Motorcycle Brakes Won’t Bleed

There are a few common culprits when your brakes won’t bleed, and we’ll cover those in this article. The brake fluid you are replacing might have become sullied with dirt or debris when it was put in originally, and that can lead to clogs in your brake line. 

Besides brake fluid that may have carried debris into the lines when it was replaced last, corrosion might be clogging your line, or any leaks might be keeping your brakes from maintaining the pressure vacuum needed to bleed them properly.

While changing out your brake fluid by bleeding the lines, you are ensuring proper function for one of the most important systems on your bike. If your brakes won’t bleed, it’s indicative of a more serious problem, often an internal one that can’t be seen. 

Lastly, if your brake fluid reservoir was not topped off during the process of bleeding your brake line, lots of air has entered the line. If you have regular brakes, no worries, you’ll just have to take a bit more time to continue to bleed the brakes. 

If your bike has Anti-Locking Brakes (ABS), you can use a scan tool to diagnose what part of your system is malfunctioning, and help you find out where the stoppage is in your line that’s keeping you from bleeding your brakes. 

How to Bleed Your Brakes Properly

Before we explain why your motorcycle brakes won’t bleed, let’s make sure you’re properly bleeding your brakes. There is a little bit of finesse to the process, and you want to make sure you’re executing the steps properly. Take a second to run through this section before you start messing with a hydraulic system on your bike.   

It should go without saying, but protect your motorcycle with rags or shop clothes before you mess with the brake fluid. Motorcycle brake fluid comes with four different DOT ratings, 3, 4, 5, and 5.1. DOT 3, 4, and 5.1 will mess up your slick paint job if it gets on the surface, so make sure to cover up before you open the reservoir or the brake fluid container! Dot 5 brake fluid is silicone-based and probably won’t mess up your paint, but who wants to find out the hard way?

  1. Open the brake fluid reservoir. This is where you’ll be adding fresh, clean brake fluid.
  2. Squeeze the brake lever. Using a pumping motion, pull back your brake lever a bunch of times. This releases any air out of your line that you’ll be able to see bubbling up. Once you’ve done this, it’s time to bleed the fluid.
  3. Attach your bleeding tool. Fit a section of clear vinyl tubing over the bleeding valve on your front brake, and place the other end in a container for the excess brake fluid. Folks, if you are going to be bleeding your own brakes, invest in a vacuum brake line bleeder. It’s relatively inexpensive, has a fitting for the bleeding valve, and will save time and headache on this project.
  4. Pump the brakes. You’ll be doing a LOT of this to build up pressure in the brake system. Keep the lever depressed while you do the next step.
  5. Using a wrench, crack open the bleeder valve. Remember to only turn the bleeder valve a ¼ turn-½ turn. Any more may cause the corrosive brake fluid to burble down your bike, causing mess or damage.
  6. Now close your bleeder valve. This will allow you to keep the pressure needed while you repeat these steps to bleed out the old fluid.
  7. Repeat steps 5 through 7 until old fluid and air bubbles are no longer present in the brake hose. Close the bleeder valve and remove your bleeder tool and excess brake fluid container. 
  8. Make sure to keep one eye on the brake fluid reservoir because you need to keep it topped off. You’re trying to keep air out of your lines, as well as push new fluid in. If the reservoir goes empty, you’ll be spending a lot more time repeating the bleeding steps to remove all the air that got into the line. This is especially important if you have ABS because you’ll need a scan tool to correct the issue.
  9. Repeat steps 4 through 9 for your rear brake. In this step, use the pressure from the right-side foot brake to pressurize the line and pump the new brake fluid into the line.

Related: How To Tell If Motorcycles Have Bad Brakes (Explained)

Now that we’ve made sure you’ve taken the appropriate steps, let’s diagnose what might be keeping your motorcycle brakes from bleeding properly!

1. You’ve Got a Lot of Air in Your Motorcycle’s Brake Line

If your hand or foot brake lever is failing, and feeling soft, maybe it’s time to overhaul your brake system. If you’ve gotten to the stage where you’re bleeding your brakes and no fluid is coming out, fear not and be patient! Overtime, in an unmaintained brake system, a good amount of air can build up in your line for one of a few reasons. 

Air in your line can be attributed to water in the brake fluid, worn-out brake pads, malfunctioning pistons in the master cylinder, or brake calipers that aren’t functioning as they should. If you or someone who was bleeding your brakes accidentally got air in the line, this can happen as well.

You might have pressured and bled a number of times now, and nothing’s coming out yet. Like I said, no fear! You might just need to press the brakes and open/shut the bleeder valve a considerable amount-more than you thought. You might be there for a while, but eventually, the brake fluid should start flowing through the hose into your excess fluid container.

2. If There’s Debris in Your Bleeder Valve, You Need to Remove it

Outside debris or corrosion might be clogging your bleeder valve ends. You might be trying to bleed your brakes, to no avail, and fluid, air or pressure just isn’t coming out. You’ll need to remove your bleeder valve screws and clean out any debris that might be stuck in the channel that the brake fluid flows out of. 

Removing your bleeder valve screws is relatively easy, but you’ll want to be careful, again, with any brake fluid that flows out, it can be corrosive, damage paint, and be a pain in the neck to clean up.

It’s easy-just unscrew the bleeding valves all the way. Once you remove them, the brake fluid will bleed all the way out, and you’ll spend a good amount of time re-pressurizing them next.

The end of the bleeder valve will have an inlet hole in it, and it may be blocked with minuscule debris that entered the system from the outside or corroded elements from an aging brake line.

You can easily remove the debris from the inlet hole by blowing compressed air through the outlet hole (the part you can see from the outside). Use a needle or something thin and hard to remove any excess debris from the inlet and outlet holes. 

If you have carb cleaner handy for getting every last bit out, feel free to use it.

Related: Do Harleys Have ABS Braking Systems? (Explained!)

3. Corrosion of Old Brake Lines Can Cause Some Serious Stoppage

Brake lines need to be replaced every four years, and the correct fluid needs to be replaced every two years. Aging and corroded lines can not only account for debris-related stoppages, but seriously damaged lines can keep your brakes from bleeding properly or even keep the fluid from running to the master cylinder properly. 

If you have removed the bleeder valve screw to clean it and there’s rust or other gunk in there, fixing the problem now won’t fix the long-term problem, and I recommend replacing your brake hose.

4. What If Your Motorcycle Brakes Quickly Go Soft and Then Won’t Bleed?

If you’re trying to bleed your brakes and nothing’s coming out, are you sure there’s anything in there at all? 

Inspect your reservoir, brake line, master cylinder, pads, and calipers for any sign of leakage or rupture. 

If any part of your motorcycle’s brake system is leaking, chances are there’s nothing left in the line to bleed but air. Look for nicks, holes, tears, or any deterioration to the structure of the brake line. You might just find the culprit to your brake-bleeding inquiry!

I’ll remind you again that the brake line or hose needs to be replaced every 4 years, and brake fluid needs to be replaced every 2 years-any longer and you’ll end up with debris and air in your line or, worse, brake failure. 

Related: Motorcycle Clutch Won’t Disengage: 12 Reasons (Explained)

A Few Notes on Anti-Locking Brake Systems

Anti-Locking Brake Systems (ABS) are more and more common on modern bikes, so there are just a couple of things to take into consideration when bleeding your brakes.

ABS systems employ a sensor, valve, and pressure pump system that regulates itself within the brake line. If you’ve diagnosed your brake-bleeding problems, and it is bleeding properly, make sure to keep topping off your reservoir to keep the air in the line.

If you get air in your line, it is going to throw the system off, and you’ll need to use a digital scan tool to properly diagnose and fix the problem in the ABS.

Sources | Ari Henning | The Motorcycle Brake System: How it Works

VicRoads.Vic.Gov.Au | Motorcycle ABS and how it works

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