In my recent post Twin Leading Shoe Drum Brakes, I went over the basics of servicing a set of front brakes from an 81 Honda CM400E, & while I feel that it was a decent article from a how to standpoint, it was pointed out to me that someone who was completely new to the world of vintage motorcycle or do it yourself mechanics might not fully understand that I was trying to convey so I thought that it would be a good idea to go over the basics of the different type of vintage motorcycle drum brakes. For the purpose of this we will examine internal expanding shoe brakes, there are some ancient motorcycles & some minibikes that use a completely different drum brake style with an external brake band around the outside of the drum and I’m not going into that here unless you give me evidence of overwhelming popular need for explanations of external band brakes. Below you will find a few illustrations along with some brief explanations of mechanically actuated single leading shoe & twin leading shoe vintage motorcycle brakes. Just for grins I’ll show you an exploded illustration of a four leading shoe drum brake at the end of this post.

First let’s examine the single leading shoe drum brake. This is the type that you are most likely to encounter on motorcycles and atvs that utilize drum brakes at one end or the other. In fact there are still some lower end bikes that still use this system today. It is simple & it works.

When the brake arm is moved the brake cam pivots pressing the shoes into the drum generating friction to stop the wheel from turning. You may have noticed that I have the shoes marked leading and trailing and here is why. with the drum rotating in a clockwise direction the bottom shoe is pushed away from the brake cam by the rotating drum thus forcing it against the brake pivot post and the drum with greater force. The front or leading edge of the brake shoe is the first part of the shoe that the rotating drum passes over as it turns whereas the trailing edge is the last edge of the friction pad in the path of drum rotation. The top shoe in this illustration is labeled the trailing shoe because the trailing edge of the shoe is forced up into the drum first. Because it is not being pushed into a fixed pivot point by the rotation of the drum, the force generated tends to push it back towards the brake cam instead of  pushing it more tightly into the drum. This means that the trailing shoe generates less stopping force than the leading shoe. There are a few advantages to this design with simplicity & reliability being at the top of the list. Another huge advantage to this design is that when you reverse the direction of wheel rotation, the trailing shoe becomes the leading shoe & the leading shoe becomes the trailing shoe. Why is this an advantage you may ask? Simple you get equal braking force whether you are going forward or reverse. While this is not that big a deal on a motorcycle it’s very important on vehicles such as atvs, tractors etc. that have reverse gears and travel backwards under power.

Up next let me throw up an illustration that I created of a simple twin leading shoe brake.

You will notice that there are still two brake shoes inside the drum but now there are two brake cams, two pivot posts, & two brake actuating arms joined together with a linkage. When the brake arms are moved it raising the leading edge of both shoes into the brake drum. Remember the advantages that the leading brake shoe has in stopping force that I told you about earlier? Now both brakes shoes are leading shoes giving you the maximum amount of friction possible from a drum brake design. This is the advantage to this design, increased stopping power. The disadvantages are that it is slightly more complicated and that it requires careful adjustment of the brake arm linkage to ensure that both shoes contact the drum at the same time. If the shoes do not open at an equal rate then only one of them will touch the drum under use giving you even less stopping power than a single leading shoe brake system. Also if you reverse the rotation of the wheel the twin leading shoes become twin trailing shoes, giving a reduced stopping power in reverse. On a motorcycle this doesn’t really matter though.

In the blog post about twin leading shoe drum brake I stated that they were the ultimate development in vintage motorcycle drum brakes, well that is almost true. There is a system that is capable of generating even more stopping force than that, the four leading shoe drum brake that was used in some exotic racing machinery. I shall not go into a huge amount of detail here except to say it is basically a pair of twin leading shoe systems mounted back to back on a common hub. I cribbed the image below from TheVincent.com.

If you are fortunate enough to own such a fine machine as an antique, Vincent, Brough, or MV Augusta racebike that uses 4 leading shoe brakes and you (or your staff mechanic) are not able to get it sorted properly, then load it into the enclosed trailer that you keep attached to your Land Rover, or Cayenne and have your butler deliver it to me along with a sackful of large unmarked bills and I will be glad to set it up for you, including a small amount of testing at a local track to make sure they are operating correctly.