rear disc brake clunks.

[jimmyhackers]

i pull the lever and get "modular" braking, upto a point then it goes "clunk" and then i get very harsh/hard braking.

i have been through and tightened every bolt. the caliper bolts are tight, the disc bolts are tight.

i cant see anything move when the "clunk" happens, and im kinda scratching my head.

any ideas?

 

[jimmyhackers]

i found the problem and fixed it.

Short answer/solution: i copper greased the rear of my pads.

long answer: the calipers/pads have a little bit of float in them to help alignment. riding about will wobble the pads to a non ideal position. under light braking force the pads rear metal surface would bind on the metal mating surface of the claiper in a non ideal position, the result would be light but still modular braking force upto a point.
however after a certain amount of braking force, the drag from the disc would move/snap the pads to their correct alignment, suddenly increasing braking force and making the "clunk noise".
the copper grease has stopped the rear of the pads from binding, alowing them to find their ideal poisiton nicely/smoothly.
the result now is hard braking that feels modular from start to finish of the lever pull, with no horrid clunk

note: if your going to try this, use high temp copper grease, use it sparingly, and make every precaution not to contaminate your discs or pads material.

 

[99t4]

Your description sounds like either poor quality caliper and/or pads, or excessively worn parts. Or missing springs? My Tektro mechanicals have a spring that holds the pads in location, and my Hayes Mag hydraulics pads have wire springs that clip them in position to the pistons.

What brand and model are yours, so we know what to stay away from.

 

[jimmyhackers]

they are tektro io.

they are 2nd hand and were a bit dirty. the worn surfaces on the rear of the pads show thats where they've been binding/rubbing.
pads are 2nd hand too, but plenty of meat left. discs are new.

there is no spring or clip. just a magnetic ring with a raised nipple in the centre, and a corrosponding dimple on the rear of the pad. there is a tang on the pad backing that goes into a groove on the caliper. there is about a 1mm of play but i think this is more of an engineered loose locator tang and a way to easily hold onto and get the pads in/out.

the clunk felt really bad, like loose bolts getting ripped out or something snapping.
they work beautifully now. i cant believe the solution was so simple.

the other solution of throwing them in the bin and buying new calipers probably would of worked also.
just goes to show, maintanance is key.