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While cleaning and oiling the chain the other day, I noticed that the rear brake was rubbing slightly when I spun the tire. Is this normal? It wasn't rubbing all the time, but only when the pads hit what could have been a high spot on the rotor. I've got about 2300 km on the bike so far (approx 1,380 mi).

Richard
 
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That is a normal condition of all disk brakes. Disk calapers have no "return springs" common to drum type brakes therefore when the brake lever/pedal is released all that happens is the system relaxes. This means that the pads still make slight contact with the disk.
 

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Drum brakes

Thanks for the answer. You guessed right - almost all of my experience has been with drum brakes. I wasn't too worried, but it's always nice to have some reassurance.

Richard
 
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Thats all true about the absence of "return springs". The only force that moves back the caliper is the deformation of the O ring around the caliper.
 
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English is not my native language, but I try to explain. The brake acts as a hydraulic pump. The brake pad is forced against the disc by a piston. Between the piston and the housing is a sealing, O- shaped. When the piston moves towards the disc, there is deformation of this ring. It sticks at the inside to the piston and at the outside to the housing. When the brake lever is released, the piston is retracted (only very little!) by the O ring because the ring tends to have the original shape. When the brake pads worn out the piston slids inside the sealing to a new position. A simple drawing would explain it more easy, but I don't have.
Its been a pretty long time since my job as motorcycle engineer, but as far as I know the basics are the same or??
 
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