Rear brake won't grip

larkim

Son's hardrock rear has Avid BB5 mechanical disc brakes witha 160mm G2 Clean Sweep rotor with Uberbike semi-metallic pads (non-stock).

Pads were replaced about 6 months ago, but at the weekend notice that they weren't grabbing - I could manually rotate the wheel even with maximum braking force applied to the lever.

I tried barrel adjusting - to no effect (just reduced the throw of the lever).

Tried cleaning the rotor with degreaser - no effect.

Tried swapping out the pads for brand new (identical) pads after degreasing the rotor - no effect. After riding 5-10 miles there is a little more grab, but I can still make the wheel rotate.

What else to try? Re-cabling? Doing "something" to the pads? New rotor?

Front has identical set up (same pads, same stock rotors) and works flawlessly.

mike hunts alpine

Try tightening the cable a little.

larkim

mike hunts alpine wrote:

Try tightening the cable a little.

Isn't that what barrel adjusting does? (Curious)

I will give it a go though.

Chunkers1980

Yes it is.

What degreaser did you use? IPA is best as it doesn't leave residue - that might still need burning off and the new pads wearing in.

jimothy78

Tightening the cable only moves the one pad closer to the rotor - the other pad doesn't move, and you need to advance it using the little dial on that side of the calliper as it wears. If there's too much of a gap there, then even at full travel you might not be pinching the rotor hard enough between the two pads.

Also, don't expect much power immediately after cleaning anything - you'll need to ride the bike and bed the brakes in before you notice the difference.

benpinnick

Barrel adjusters have little effect on mechanical brakes I find. Adjust the cable at the caliper end.

njee20

Is the lever coming to the bars, or is the lever solid, but the brake not working? If the former then the gap between the pads/rotor is too large - check the static pad, and adjust the cable as necessary. If the latter then something else is going on, but that would be very odd indeed.

larkim

Its the former - but the thing is, it's not coming towards the grips particularly far. It is feeling a little spongy though, so perhaps you're right - its just a case of adjusting the static pad positioning.

njee20

Huh? It either comes to the bar, or it doesn't? Does the lever bottom out on the grip, or does it stop at some point before then?

Cables can't really be spongey, cheap outer can compress quite a bit though, such that you can keep pulling the lever once the pads have contacted the rotor.

The Rookie

Have a look at the calliper, if you can see daylight between the disc and pad it's not adjusted properly, mechanical discs give the best leverage ratio at the start of the pull so you absolutely have to minimise lever travel to get the best braking, don't forget that both pads need adjusting, the static one (that is the one that doesn't move when you pull the lever) and the moving one.

thistle_

The cable isn't frayed and about to snap? Normally you would have other problems too such as lever not springing back.

abarth_1200

Missed a vital question from another member.

What degreaser did you use, you need disc brake cleaner or ipa. Not regular degreaser