Rear drum brake overhaul

Discussion in 'Scooter Guides' started by px166bajaj, Dec 17, 2008.

  1. px166bajaj

    px166bajaj Active Member

    Messages:
    1,367
    This was originally writted for the Chinese Scooter Club's forum, so it may not be exactly the same ay what you have, but it will be similar.

    This is a guide to dismantling and overhauling drum brakes. While your own scooter may not be exactly the same as mine, the principles are the same. Some bikes have front drums as well as rear, and this procedure is essentially the same for those as well.

    Drum brakes are very simple in operation. Mechanical force via a cable from the handlebar brake lever is used to pull a lever at the hub. This second lever turns a pivot which passes into the hub of the wheel. The inner end of this pivot is flat and sits between one end of the brake "shoes", in the hub. These curved "shoes" are attached to the brake "backplate". The "drum" is part of the wheel and rotates with it. When the brake lever is pulled, it causes the brake pivot to turn and force the brake shoes apart, and come into contact with the rotating drum.

    There are three main problems which occur with these brakes.
    1. Out of adjustment. You pull the brake lever, but not very much happens.
    2. Shoes worn out. Symptom similar to 1. but accompanied by a teeth jarring squeal, as the metal of the shoes hits the metal of the drum.
    3. Pivot seized. The brake works fine, but will not release when you let go of the lever. This can bring the bike to a complete halt or just sap power if it's only partially seized.

    My Chunlan was suffering from a seized rear brake, so it was the perfect opportunity to do a brake overhaul guide.

    Ok, first thing is the exhaust has to come off! This is a pain but grit your teeth because the job cant be done without removing the exhaust pipe. I won't describe the exhaust procedure, because they are all different. Suffice it to say hat there are 2 nuts at the engine end of things and 2 or 3 along the length of the exhaust. Be comforted that my Chunlan exhaust is way crazier than anything you will have to deal with! :lol:

    Anyway, exhaust off....
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    On the Chunlan there is a shock absorber and a mounting for it behind the exhaust. Depending on model you may or may not have one of these. If you have remove it by taking of the main wheel spindle nut and shock absorber retaining bolt off. The Wheel spindle bolt will go round and round unless you get an assistant to put the brake on while you undo it.
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    You should be left with a wheel with nothing obstructing its removal. Grab it with both hands and rock it to and fro and withdraw it from the spindle. Here I've removed the wheel and you can finally see the "drum" and the "shoes"
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    Here I'm removing the shoes which are held together on the backplate mountings as a pair by small springs. Some bikes have a giant bendy "Horshoe" spring which holds the shoes together. Tilt out the top shoe to 90 degrees and pull sharply and they will come away as a pair. These shoes were OK so didn't need replacing, but you will see if the Asbestos (hence the gloves) layer has worn away to metal. If it has, or if there isn't much left, replace them.
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    Next we have to remove the pivot. It's the protruding bit on the left of the hub backplate.
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    In this picture you can see how the lever on the outside of the hub connects to the pivot and carries through to the inside of the hub.
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    Remove the brake adjuster nut... You will need to hold the cable with pliers or a mole wrench while undoing the adjuster nut with a spanner.
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    Then remove the brake lever securing bolt. You may have a nut and bolt.
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    Tap the lever gently with a hammer and it should come free.
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    My pivot was partially seized, so I had to "help" it out of its hole. Because there was no room to tap it with a hammer from the outside, I held it with a mole wrench and tapped the wrench until it withdrew into the hub.
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    Here's the little bugger!
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    Clean up time. The pivot was seized because of corrosion and dirt on the pivot itself and the hole it fits through. I put the pivot in the drill and rotated it while dremeling it. Or you could just use fine emery paper to clean off any corrosion.
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    Then I sprayed brake cleaner onto the backplate and waited for it to dry. Then I dremelled it. You may not need to dremel yours but my bikes quite old and there was a bit of corrosion to clean out.
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    Next, I cut a strip of fine emery paper and taped it to a drill bit, to clean the inside of the pivot hole.
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    Finally, a thin layer of copper grease was applied to the moving parts. Copper grease is designed for high temperature applications such as brakes and exhausts. NEVER use ordinary grease inside a brake drum, as it may melt and contaminate your brake shoes.
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    Refit the brake shoes. This is not always easy, but generally, fit one shoe and stretch the other into position until it "snaps" onto the moving pivot pin at one end and the fixed pivot at the other. Once the shoes are on, refit the outer brake lever, and the brake adjuster nut.
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    Then bung the wheel and exhaust on.
    Adjust the brake, by tightening up the nut on the end of the cable. Don't overtighten the adjuster, as it may tighten up when you sit on the bike. Check that it isn't too tight or too loose before riding anywhere.
    Too loose-handlebar brake lever travels almost all the way back to the bar before the brake comes on.
    Too tight-almost no movement at the handlebar lever, and/or the brake rubs and prevents easy movement of the wheel.

    Let me know if you have any questions ;)
     
    Scouser likes this.

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