Harley Ironhead Rear Drum Brake and Alignment

With his ‘77 Ironhead Sportster still raised up on the table lift, Kevin is now moving to the rear of the motorcycle for service and inspection of the Harley rear drum brake and the rest of the surrounding sub assembly.

The Harley rear drum brake assembly on this 1977 Sportster is fully mechanical. There is no master cylinder, brake hose, or brake fluid. Rather, there is a brake pedal that, when depressed, actuates a brake cable. The brake cable pulls on a lever that rotates a cam inside the brake drum. The cam rotation then pushes the brake shoes outward against the brake drum to create stopping power through friction.

The brake lever has a spring that returns the cam and shoes back to their resting position. This Harley rear drum braking system takes more maintenance than a hydraulic assembly and is much less effective than a disc brake assembly. However, when you have a Harley rear drum brake assembly that consists of OEM parts that are in good working order and are properly maintained and serviced, the system will provide sufficient braking power for an old Sportster.

Kevin loosens the rear axle nut, the rear brake drum stay, and the axle adjuster jam nuts. He rotates the rear wheel to find the tightest area of the chain and proceeds to equally adjust the right and left side axle adjusters until he achieves ¹⁄₂” of free play in the drive chain. Kevin uses a caliper to aid in setting the axle adjusters equally. Using a caliper or a scale is usually sufficiently accurate for this maintenance procedure. The only time it may not be is if the swingarm, axle, or axle adjusters are worn, damaged, or incorrect.

After the chain and axle are adjusted to spec, the axle nut should be tightened and the chain should be checked once again. Sometimes chain tension will be affected by the tightening of the axle and subsequent flexing of the swingarm. With correct chain tension achieved, Kevin tightens the axle nut, axle adjuster jam nuts, and brake stay. Chain adjustment and wheel alignment are vitally important not only for proper function but also for rider safety.

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