How to Fix Mushy, Spongy or Soft Motorcycle Brakes

Are you noticing that your brakes do not feel as crisp and responsive as they should be? Then it’s time for an inspection. Fortunately, motorcycle brakes are relatively straightforward, accessible and can be diagnosed and repaired with moderate mechanical skills and basic hand tools.

Over time braking systems will gradually drift out of specification, because of wear and environmental factors. If your brakes are inspected and maintained on a regular basis they should be trouble free. But as with any mechanical system, issues can arise at any time. The end results are the same, poor braking performance.

Brake Inspection & Repair Steps

Braking systems all use the same fundamental hydraulic-mechanical design.

So, these basic inspection and maintenance steps apply to all types;

  • Brake Fluid Level – check, add if required,
  • Fluid Condition & Age – replace fluid,
  • Bleed Brakes – remove trapped air,
  • Brake Pads – replace, upgrade,
  • Brake Lines – replace, upgrade braided stainless-steel lines,
  • Brake Rotor – replace, upgrade.

Brake System Design

Modern braking systems are practically all hydraulically activated, in other words, fluid pressure is used to engage the brakes. When you pull in the front brake lever or step on the rear brake pedal this mechanical motion is transferred into the brake fluid which in turn move friction pads against the wheel rotor. This “pinching” effect of the pads to the wheel rotor provides all the stopping force.

It is rare to see drum brakes on large road motorcycles these days. On very few street motorcycles, the rear brake can come with a shoe & drum design. Instead of using hydraulic fluid, a cable mechanically moves a set of brake shoes against the inner wheel drum. The same principle the same as a hydraulic design just not as effective, precise or efficient.

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Inspection & Diagnosis

Before starting it is good to measure how well the brakes are currently working. The primary measurement here is the distance required to stop from a constant speed. Stopping distances are usually included in new model road testing. While it might be impractical for you to reproduce this test to the standards that professional testing does, a baseline stopping distance is a good starting point to have – since “feeling spongy” is very subjective. So, it’s a good idea to have a basic test you can perform, just make sure it is consistent and repeatable.

Start with inspecting the brake fluid level. Often the level can be seen through a semi-transparent reservoir or by a built-in sight-glass. If low try topping it up. If brake fluid has gone very low you may now have air in the lines (bleeding required, see below). While checking note the fluid color versus new – if it is off color, looks dirty or watery it is time to flush out the old fluid.

Brake Fluid Specification – you must know what brake fluid is needed for your make and model. This “DOT” spec is very often stamped on the brake reservoir/master cylinder itself. If not check the owners or service manual.

DOT 3, 4, 5 and 5.1 are current specifications. DOT 3, 4 and 5.1 are commonly used for motorcycles, although DOT 3 is old. DOT 3, 4 and 5.1 all have the same glycol base chemistry. DOT 5.1 is synthetic and not compatible – so never use DOT 5 to top up other DOT spec’d fluids. I would take this a step further, and not mix two manufacturer’s products. Brake fluid contains additives such as corrosion inhibitors and lubricants, which may not be fully compatible between brands.

If in an emergency you had to mix DOT 3, 4 or 5.1 then plan on completely flushing and replacing your system with the correct DOT spec as soon as possible.

If you have a unique situation where DOT 5.1 was originally supplied (some Harleys, for example, had this), and you wish to switch to DOT 5 for example, it will require a complete flush, cleaning and rebuild. Since the rubber & seals will have absorbed DOT 5.1 fluid and there might be negative chemical reactions between the new fluid and old fluid soaked components a rebuild is recommended.

Spongy Response

Brake pads and rotors wear slowly over time, and as wear occurs slack is taken up by brake fluid. Braking response and performance will slowly degrade and it will not be noticeable as it does.

Brake fluid does “wear” also. The fluid becomes contaminated with air or moisture, and even accumulated dirt. Typically after one-year brake fluid will have absorbed up to 4% water. Air will also get into the system. The fluid will not be as effective or responsive since trapped air will compress absorbing vital braking energy and making the brakes feel spongy and mushy.

Another area that can cause spongy brakes are the hydraulic lines. As they age they can soften and bulge slightly under pressure. Again redirecting braking force to expanding the brake line and not to the pads. In some cases, poor design and materials can be a problem from new, this is when “performance” upgrades may be useful.

Brake Fluid Change

Before starting work – be aware that brake fluid will damage painted & chromed surfaces, and is poisonous. Use protective gloves, and eye protection, and handle brake fluid carefully. I use shop rags to cover the tank and fenders just in case.

If you do not know when the fluid was last changed – change it. Check your service manual or reservoir for exact DOT specification. Review the factory recommended procedure.

This is a typical fluid change process;

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  • Put the motorcycle on its center stand, or lift,
  • The front wheel should be off the ground. You may need to put weight on the rear seat to raise the front wheel,
  • Move handlebars so brake fluid reservoir’s top is sitting flat,
  • Cover all painted and chrome surfaces with rags,
  • Clean the reservoir before opening it, take lid or cap off,
  • Place a drain tube on the caliper bleeder nipple screw,
  • Route the tube to a waste container,
  • Partially fill this waste container with new fluid,
  • Open and allow fluid to drain into a container,
  • Gentle & slow lever movement will help push the fluid out,
  • Partially drain the reservoir, ideally to half full,
  • Tighten the bleeder nipple enough to stop the flow,
  • Refill the reservoir with new fluid, poor slowly and try not to mix old with new,
  • Repeat until all fluid coming out is fresh and new.

If done carefully you will not introduce any air in the brake line and will not need to bleed the brakes. But brake bleeding is not hard to do if needed.

Bleed Brakes

One of the most common causes of soft or mushy braking is air in brake fluid. Besides the brakes being mushy another symptom is that braking improves with repeated lever/pedal pulls. Pumping the lever compresses the air and momentarily reduces the problem sending more braking energy directly to the pads & rotors.

After changing the fluid, often bleeding is required. The process forces new fluid through the system thereby pushing out any older fluid that contains air. The steps will be outlined in your service manual.

When the front and rear brakes are independent systems and are not ABS the process is basically the same as changing your brake fluid (above). If the front and rear are interconnected (linked, LBS), or if ABS is in use you must follow the factory instructions. Brakes are critical, this is not an area where you can risk guessing how it’s done.

Pads and Rotors

Pads and rotors are designed to wear, eventually, replacement is required. However, rotors will typically outlast a set of pads, so they do not need to be replaced together.

Brake pads can be damaged by oil contamination, and even cleaning products if used without discrimination.

For example, if you oil the rotors before storage and then forget to completely clean them off or your pads will suffer. Also, be careful about using silicon-based cleaners around pads and rotors. Silicon contamination will greatly reduce the needed friction for effective braking.

Inspect pads for excessive and uneven wear, this could indicate a sticking caliper piston, or that the pads are not moving freely due to a lack of lubrication. Take notice of any major grooves in the rotor, if so check the pads for embedded road debris. the damage may already be done, but remove debris to avoid further issues and maximize pad to rotor contact.

When replacing do not shop on price, invest in your safety go with the best quality pads and rotors your budget can justify.

Cables & Shoes

Some motorcycles still come with mechanical brakes, on the rear. Braking is activated by a cable that moves brakes shoes against a wheel drum (integrated into the center of the wheel). Cables will stretch over time and need adjustment to be effective. Once the cable is stretched to its limits it needs replacement. Wear will also occur around cable ends, bushings, and fittings. Check all these points for slack and unwanted movement. All these wear points will combine together and result in lever movement being wasted before actually engaging your brakes.

Thoroughly inspect all moving components for slack and wear, replace as needed. If recommended, use a cable lubricant. Note that some cables are Teflon, or similarly lined and will degrade if lubricated (there usually is a warning in your owners manual or instructions on replacement products).

Be aware of economy cables that may stretchiness simply built in, because they are made as cheap as possible. These may even feel spongy from brand new.

Brake shoes will become less effective as they wear down. Often there is a wear indicator on the outside, pointer on the brake arm. Brake shoes can become “glazed”. As the name implies the shoe’s friction surface gets hard and shiny from heat, pressure, and moisture, resulting in reduced friction. Removing glazing is done with high grit sandpaper until it is visually not shiny.

Braided Steel Lines

Typically rubber brake lines with some steel tube sections are used. Over time this rubber becomes more flexible (expandable). When you apply the brakes some of the pressure that should be moving the pads against rotors is going to expanding these lines.

Simply replacing old rubber lines with new OEM lines will usually restore as-new performance. While there is much debate over braided lines there are technical reasons to expect them to perform better than standard issue.

To prevent undesirable expansion a braided steel covering is used to contain the rubber. They are essentially a hybrid cross between all rubber and all steel tubing. In theory, the outer casing of braided stainless steel keeps the inner brake line from expanding and this sends more fluid pressure to the pads resulting in more braking force. As a bonus, the outer steel covering provides a layer of protection against the lines being nicked, cut or sun damaged. Of course, the quality of design, manufacture, and materials will determine if they make a difference.

Braided brake lines are considered a performance upgrade, they are not required to fix mushy braking. They are available as a direct fit replacement for most popular brands and often come in complete kits with all required washers, o-rings, and seals.

As a bonus, the covering adds some protection against cuts and abrasions, while rare they are still possibilities. Putting on braided lines also offers another way to personalize your ride, since they are offered stainless and many other colors.

Effects of Heat

Heated is a byproduct of braking. When too much heat is accumulated you may feel the brakes “fade”, and not work as well as when cold. Avoid overloading your motorcycle and riding conditions that require a lot of stop-and-go or continuous braking if possible. Upgrade to high-quality performance brake pads and possibly rotors. All rotors should be slotted or drilled to dissipate heat more effectively.

If you notice strong pulsing vibration when the brakes hot the rotors may be warping due to the heat. As the rotors wear thin warping is more likely to occur, and will be permanent. A warped rotor feels very obvious and not at all normal.

To fix a warped rotor replacement is needed – use OEM or better quality. Always go for a slotted or drilled rotor design, for better heat shedding. High-quality performance pads are also a sensible upgrade to combat heat beat.

ABS Considerations

If your motorcycle has ABS (anti-lock braking) or even if it doesn’t, get a service manual and be aware of what is required to service the brakes properly for your specific model.

For example, some manufacturers require the dealer “activates” the ABS module with a specialized computer before servicing, with a specialized tool. Activation releases fluid in the ABS unit for complete flushing. Other systems may have accumulators that pressurize the fluid, needing specific steps or tools to properly work on.

Having ABS by itself doesn’t necessarily mean a dealer needs to do the work. However, you just need to be aware of before starting on any brake work, even just replacing brake pads could be different than older less hi-tech machines.

Summing it Up

Brakes are not complicated they generally just do their job with day after day. By following recommended scheduled maintained your brakes will continue to operate just fine. However, if notice odd or poor performance do not put off investigating and fixing any problems. Small performance losses will build up slowly and if not fixed may surprise you probably at the worst time possible.

Braking Tips

  • When riding in the rain or just moist conditions, lightly apply your brakes every so often. This will remove some moisture and make them more effective and ready to use.
  • Ride defensively – have a least one, or two fingers on the front brake leaver – milliseconds that this saves could save your life. For the rear, be conscious of where your foot is, and keep it close to the pedal. This matters a lot more when in heavy traffic.
  • Use engine braking, this is when you purposely downshift as your decelerate (letting off the throttle) so the engine drag assists with braking. With practice, engine braking is very effective and will become second nature.

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