Tech Answer: Brakes

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Tech Answer: Brakes

Postby poopShotgun » Mon Apr 23, 2007 7:10 pm

Changing or cleaning brake pads is often neccesary after a long summer of riding and can improve the safety of the bike, especially in inclimate conditions. Tightening the brake cables can often produce the same results since the pads will degrade over time and the cables will stretch. Disk and drum brakes will be handled seperately here.

When should this be done?

Anytime the brakes feel sloppy, slow to engage, make a screeching noise, or stutter when stopping.

The Procedure:

Drum Brakes ->
Check your manual on how to remove the front or rear hub. For a pre-79 Vespa, remove the outer axle nut cover (the chrome dome), remove the cotter pin, then loosen the axle (castle) nut. The axle nut is easier to remove if the tire is on the ground at this point. For added leverage, you can often squeeze the appropriate brake lever while loosening. Remove the washer, prop the bike up on a milk-crate, and take off the tire. Get a rubber mallet and whack the hub lightly from behind a few times in different locations until it pops loose. Remove the hub. You now have access to the pads.

Removing the pads depends on your setup. First, remove the retaining clips on the pivot posts. For the front brakes there is one post, the rear has two. You'll also notice the brake mechanism, which is a post opposite that the pads are held against with a spring. Slowly work one pad (or the top-most pad) off the pivot post and brake mechanism until it is hanging loose. You can easily remove the second pad in the same manner.

Now that the pads are removed, inspect them to ensure they have worn evenly and still have enough material to engage. The pad itself is attached to the arm and is made from organic and metallic materials. It'll look a lot different from the arm. You should replace your brake pads when they have worn down to about 1mm in thickness. For a vintage bike they could easily last longer, but it is always better to be safe than sorry. If the pads are in good condition. clean out the braking area, the hub, pads, and posts with a soft cloth. You can also use compressed air (or blow on it). The dust you see is the worn-off brake material. Unsubstantiated reports also claim you can douse the pads in gasoline and set them on fire, but I have never personally tried this.

The brakes are put back together in the reverse manner. It is easier to ease the brake arms onto the pivot and mechanism posts if you connect the two arms via spring first. Do one, then the other.

Once everything is done, test the bike and adjust your brake cable to your liking. Make sure you can engage them fully if need be, but not too stiffly that the wheel doesn't roll freely when not engaged.

Disk Brakes ->
I have no experience with disk brakes on a scooter, but I do know that the pads are much easier to inspect. You can also check the disk itself for warpage or deposits with simple spot checks before riding. The pads will have to be changed at different intervals because they often have posts sticking up from the caliper. This will cause screeching when the brake is engaged and is a sure sign you should change the pads as the posts could damage the disk.

Removal and renewal should be accomplished according to the manufacturer's recommended procedure. You will likely have to bleed and fill the hydraulics when changing the pads as well; Ensure you have the correct fluids before starting.

Special Situations
If your brakes engage in a stuttering manner, you should check the hub for looseness and also to see if it is off true (it wobbles when tightly attached). If the hub if off true, replace the hub, brakes pads, axle nut, and washer. You should also inspect the axle itself to see if it is off true and replace it if needed. This may also be caused by excess brake dust (the material worn off the pad), so it is a good idea to check the pads before purchasing a new hub.

If the brakes engage with little play (either fully on or fully off, no play), you should clean the pads and braking area of brake dust. If that does not help, change the brake pads.
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