Ossa Brakes

[nickyburnell]

Hi all. Anybody ever had any success uprating, modding or making them work! Ossa MAR, I am quite heavy and it has no brakes. Is there a recognised disk, or bigger drum mod?

Thanks to all

Nick

[dgshannon]

Hi all. Anybody ever had any success uprating, modding or making them work! Ossa MAR, I am quite heavy and it has no brakes. Is there a recognised disk, or bigger drum mod?

Thanks to all

Nick

Nick,

Trying to get good brakes is a common problem, on all the old bikes. One of the most common mods is to shim the pivot point, of the brake shoes. Your brake arm only causes one end of the shoes to expand. The other end of the shoes are on a fixed pivot point. As the shoes, or pivot point itself, wear down, the shoe surface is getting further and further away from the drum surface. This can cause the shoes to only touch the drum, on a small area of their total surface, typically toward the end where your brake arm is expanding them apart. Down on the pivot point end, the shoes may not even be coming into contact with the drum, no matter how hard you pull the lever.

The mod is to make a shim that fits over the pivot point. This open up the shoes, on that end, placing them closer to the drum surface, when at rest. Ideally, you want the entire surface of the brake shoe, to come in contact with the drum, when you apply pressure on the lever. You can make the shims out of soft brass, tin, etc. I have even heard of folks using brass bullet casings. However you accomplish it, done right, it will make a HUGE difference in you brake performance.

[nickyburnell]

Hi all. Anybody ever had any success uprating, modding or making them work! Ossa MAR, I am quite heavy and it has no brakes. Is there a recognised disk, or bigger drum mod?

Thanks to all

Nick

Nick,

Trying to get good brakes is a common problem, on all the old bikes. One of the most common mods is to shim the pivot point, of the brake shoes. Your brake arm only causes one end of the shoes to expand. The other end of the shoes are on a fixed pivot point. As the shoes, or pivot point itself, wear down, the shoe surface is getting further and further away from the drum surface. This can cause the shoes to only touch the drum, on a small area of their total surface, typically toward the end where your brake arm is expanding them apart. Down on the pivot point end, the shoes may not even be coming into contact with the drum, no matter how hard you pull the lever.

The mod is to make a shim that fits over the pivot point. This open up the shoes, on that end, placing them closer to the drum surface, when at rest. Ideally, you want the entire surface of the brake shoe, to come in contact with the drum, when you apply pressure on the lever. You can make the shims out of soft brass, tin, etc. I have even heard of folks using brass bullet casings. However you accomplish it, done right, it will make a HUGE difference in you brake performance.

Many thanks, makes sense, single leading shoe sort of thing... ANy recomendations on brake material?

Nick

[feetupfun]

After lots of attention to detail, EBC shoes work great in my MAR. As well as what Jay said to do with the shoe pivot, there are a couple of other things that will help maximise the contact area:

1 If the drum surface is at all grooved, it will take ages to bed in the new linings. Taking a skim in a lathe to give a true surface may be needed.

2 Some OSSA front backing plates hold the shoes a bit eccentric to the drum. If yours won't centre properly when you fit the wheel, you may need to enlarge the axle hole a bit.

3 You should radius any new linings to match the drum diameter. I usually do this by repeated cycles of riding-inspection-shaping-riding.

As well as the contact area, a new, high quality, low friction cable and a lever assembly with a high leverage ratio both make a big difference. an Amal lever assembly works well for me on the MAR.

There is nothing wrong per se with MAR front brakes. With careful setup they can be made as good as anything else of the era.