Tech Talk – A Trip Down Memory Lane: Harley Brake Systems, Circa 1936 to 1985
November 28, 2011 | By: Scott Holton
This month we’re going to talk about early brake systems, but before we do that, let’s think about what a brake actually does for a living. Simply put, a brake converts mechanical energy into thermal energy by applying friction from the pad or the shoe to the disc or the drum.
Now we’ve got that out of the way, time for some history. Early in what we call the modern era of motorcycles — from 1942 to 1971 — Mother Harley used drum brakes to slow things down. From 1936 to 1957, rear brakes were of the mechanical variety. A brake pedal linked to a crossover shaft, rear linkage and brake arm converted leg power to stopping power. This system worked OK in its day, but was prone to wear at every mechanical connection.
Many years ago I learned the hard way how much trouble you can get into when one of these points break or lose their cotter key. Needless to say, after I peeled myself off the side of Farmer John’s Pontiac, I paid a lot more attention to the condition of each linkage. While Sportsters retained mechanical drum rear brakes until 1979, the first improvements Harley made on Big Twins occurred in 1958 when hydraulic drums where first introduced. A ¾-inch bore Wagner Lockheed master cylinder actuated things, with shoes the same width as the earlier mechanical brake.
Then in 1963, the shoes and drums were made wider for a larger braking surface area. This fairly stout configuration was used until 1972, after which rear disc brakes where introduced. The reason manufacturers went to disc brakes has nothing to do with initial braking performance. Drum brakes are actually more efficient with their greater contact area, but are also more prone to fade after repeated use. Once the drum gets hot, we can’t convert energy as efficiently.
Disc brakes don’t have the same swept area, but are vastly superior in the heat-dissipation department. This allows the brake to be applied more often with a shorter recovery time. Disc brakes from various manufacturers have been in use on the rear of our beloved Harleys since 1973.
Front brakes were drums from 1936 to 1971, followed by the upgrade to single discs in 72. These drum brakes were notorious for not working well. Harley riders everywhere where glad this change was made because 70 percent of a bike’s total braking power is in the front brake.
In the late ’70s, dual discs were released. This improved stopping power even more. Today’s late-model Harley may be equipped with either type. After 1982, dual disc applications used a different bore size master cylinder. This is important to remember if you are updating your handlebar controls.
The aftermarket has a variety of selections available to improve your stopping power. Performance Machine’s handiwork is jewel-like in its precision. GMA has a fine product for the more economically minded. And Milwaukee Twins, Hawg-Halters, Brembo, Revtech and Billet Concepts are some of the other manufacturers that J&P Cycles presently carries. The thing we have to pay attention to is what bore size the new brake requires. Rear brakes can require 5/8ths (GMA) or 3/4ths. And the truth is, I’ve never seen a current aftermarket caliper that doesn’t outperform the stock brakes. That’s just a fact of life.
Rotors are fast becoming a highlighted feature on many bikes, and polished stainless steel appears to be one of our more popular sellers. Problem is, this can result in brake pad compatibility conflicts, a situation that can be addressed by changing pads to address our needs. Brake pads come in a variety of compositions. Organic pads are the least aggressive (less stopping power) but they are certainly more gentle on the rotors, which improves rotor longevity. On the other end of the spectrum, sintered metal pads are the most aggressive, handing out a higher stopping ability at the price of increased disc wear. There are pads specifically designed for use with polished rotors to reduce wear. What’s best for you? To make that decision, you need to think about how you ride. Do you have a smaller bike that you insist on throwing hard into the corners? Then use a more aggressive pad. Would you describe yourself as more of a cruiser? Then a softer pad’s for you. Are you tricking things out for maximum appearance? Polished rotors with a pad designed for that use is your ticket.
But that’s why we’ve got tech specialists here at J&P Cycles who can answer your specific questions about brakes — and anything else that sits on two wheels. Give us a call.