Harley-Davidson Brake Repair and Rebuild

In this article, we're going to perform a purely practical operation, consisting of the repair and reconstruction of the rear brake system.
Although in this specific case we have chosen the brake of a Harley-Davidson Softail model, the truth is that most brake calipers and pumps are very similar, and the procedures are similar, so you can apply the methods used for other motorcycle models, of course, using common sense and within your possibilities, since we are talking about a very important element for our safety.

The problem
Brake system repairs are generally performed when the motorcycle has accumulated a significant amount of mileage, and we begin to notice excessive friction between the pads and the brake disc when we release the lever or pedal (the pads don't return properly to their resting position). In extreme cases, this can generate excessive heat due to friction and cause the brake to lock up. If this happens and we continue riding the motorcycle, we will reach a complete lockup and deform the disc, rendering it unusable.

The solution
System repair consists of installing a brake master cylinder repair kit, a caliper repair kit, and a new disc if the disc is deformed.

Likewise, we'll need brake fluid (DOT 4 or DOT 5, depending on the year and model if it's an HD). It's important to use the correct fluid, as they're generally not compatible, and if you make a mistake, the brakes will fail when you need them most. You can find this information on the master cylinder caps or in the service manual.

We start with the wheel
We will start by uninstalling the wheel from the vehicle to remove the brake disc.

What we will do next is check the deformation of the same, we will do this with a straight edge and a set of feeler gauges; if the maximum clearance specified in the workshop book is exceeded, the disc must be replaced.

In the next step, we will install the new brake disc. It is advisable to also replace the mounting bolts. In any case, we will use a small drop of “strong” threadlocker on each bolt and tighten it with a torque wrench to the torque specified by the manufacturer.

We will normally use a star tightening sequence.

After installation, we will reassemble the wheel following the procedures and tightening instructions in the manual (I am insistent on this topic, but it is essential to achieve a good job).

We continue with the clamp

To work on the brake caliper, the easiest way is to remove it from the motorcycle so we can move it to the workbench. We'll remove the piston using compressed air or a special tool.

With the piston out, we can replace the square O-ring, which is responsible for the piston and pads retracting when we release the brake. To avoid damaging the O-ring, we'll handle it with a plastic or wooden object.

Now we can replace the rubbers with those from the rebuild kit. There's one key factor in successfully repairing a braking system: cleanliness. We must be very careful to prevent dust or foreign bodies from settling inside the components, and we'll clean everything with alcohol.
Once everything is clean, we will lubricate the seal with a specific product or brake fluid and reinstall the piston.

After this we install the brake caliper and pads in their location on the motorcycle.

Finally the brake pump
Now we just need to work on the brake pump. After removing it from the motorcycle, we'll loosen the main mounting nut, allowing us to remove the piston and its internal mechanism.

We will use the same cleaning and assembly procedures as for the brake caliper and replace the components supplied in the kit.

We reinstall the brake master cylinder and all that's left is to fill it with the appropriate brake fluid and "bleed" the system, that is, remove all air bubbles so that only fluid remains inside the components and hoses.
There are many different systems for performing this operation (in another article we will talk about it and compare them), on this occasion we have used a Mityvac manual vacuum pump, a tool specified in the HD manual instructions.

Final checks
As always, we'll go over everything again to make sure everything was done correctly, and we'll gradually test the bike on the road until we're sure everything is working properly. Ride hard, brake hard!

Frank Burguera

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