Monday, October 15, 2012

Design Element: Rod Brakes

Most people are familiar with normal cable hand brakes. Basically what happens is that you have a metal braided cable attached to a handle on the bars. When you squeeze the handle, the cable tightens. On the other end of the cable is a set of calipers. These fingers have rubber pads attached that pinch the sides of the rim as you squeeze the handle.


The Raleigh Sports here has cables. The black rubber tubes house steel cables inside. The steel cables move when you squeeze the brake levers and that silver caliper pinches the wheel. Just above everyone who rides a modern bike has seen this in one form or another.

There are other ways of moving the brakes though. Instead of using cables, you can use solid metal rods attached to hinges.




 These picture show rod brakes. These metal rods attach to the handle bars. When you squeeze the brake lever this time, it pulls on the rods, which in turn applies the brakes. The front brakes are pretty straight forward- you the rods get pulled up and apply the brake shoes or brake drum. If you have brake shoes, a stirrup applies the two pads to the inside circumference of the rim. If you have brake drums, as this green Raleigh has, it causes internal brakes in the hub to expand and rub on the inside of the hub shell.


When you need to turn a corner, you cant just bend a rod as you would a cable. So a hinge is attached to the bike frame. When the front rod goes up, the hinge pivots and pulls on a cable running down the bike, which in turn pulls on a second hinge near the wheel, which then pulls on the brakes and applies them. It's like a series of elbows all bending to move the bones of the system.

A basic description of adjusting rod brakes:



Rod brakes can be adjusted. In the picture above you see some hex nuts where the small rods pass into the larger ones.

The front:

You loosen those hex nuts to adjust the handle pull for softness or hardness in applying the brakes. First you loosen those nuts so the small rods leading to the handle bars are loose. With a stirrup model, you adjust the brake pads to sit closely to the rim without touching it. You're looking at the gap in the picture above denoted by the red line added to the picture. If need be, move the rod peg guides. Basically you want the rods resting close to the rim without touching it. Then, re-tighten the nuts linking the mechanism to the small handlebar rods.

The back:

If you're doing the back brakes, there is a second linkage below the bottom bracket similar to the one you see at the front. When you do the back brakes, loosen both the handle bar small rod nuts (seen above in the picture) and the similar adjustment nut under the bottom bracket. That way, everything in the system is loose and ready for adjustment. Then set the back brakes close to the rim at rest. Move the stirrup peg guides if need be. Once the pads rest closely to the rim without touching it, re-tighten the adjustment nuts under the bottom bracket and up at the front of the bike. You can do the job using a decent wrench or socket.

If a nut is frozen, use Kroil or Liquid Wrench and let it soak into the joint. It is indeed possible to crack the adjustment parts at the joint where that nut is. Work slowly.

Replacing pads:

The pads are held in place with a nut to the stirrups. When you want to replace these, remove the pads and replace with new ones. When you replace and try to mimic the contour of the inside of the rim as best you can. They will be a little weird until they wear in, if they're the flat profile pads. The really good pads come with their shapes pre-contoured to fir the rim. You can use either, and both work reasonably well once you wear the flat ones in. You will probably have to re-adjust both the front and back brakes once the new pads are on. Use the method I describe above.

A final caution:

Remember that because you are using the inside of the rim's surface with stirrup/rod brakes, if the pads hit the spokes, you're in for trouble. Your wheel needs to be trued for both hop (radial movement) and wobble (lateral movement). Hop is more annoying than anything, but wobble can be dangerous if the pads are going to hit the spokes or nipples. Test spin your wheel and test your brakes several times before riding them, to make sure you're ready to roll.

Also, only certain rims can be used with rod/stirrup brakes. These are the Raleigh/Westrick and Westwood rims with wide, flat top profiles that feature a ridge in the middle where the spokes are.






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