Hi all,

i recently bought a bike online and it requires some assembly. everything was set up save for the rear brakes which i'm currently having an issue with it.

the front brake is connected to the left handlebar and so far, no issue with it.

the rear brake is connected to the right handlebar and is giving me major issue.



basically:-
(1) when the handlebar is straight, depressing the brake lever engages the brake;
(2) BUT whenever i turn the handlebar right then the brake automatically engages (see GIF)
(3) whenever i turn the handlebar left, the cable seems to have loosen and depress the brake lever doesn't engages the brake.

did i do something wrong?

append below is the picture of how i assemble the cable to the calipers.

It is possible that you do not have enough slack in your cable/cable housing. You need to leave some access cable so that when you turn the handlebars there is enough cable so that it doesn't pinch on your discs causing unintended braking. If the cable housing already cut short, then need to buy new cable housing and cables.

If you are not very good at troubleshooting, just bring it to a bike shop, sometimes these things get solved very fast by the bike mechanics while we need to trouble-shoot for a long time. Last time I like to trouble shoot and fix things myself but sometimes it gets very frustrating and time-consuming.

i haven't cut the cables yet and there's still plenty of it left.

the thing is, i don't have a car big enough to accommodate the bike so i'm pretty much stuck with DIY and i don't dare to cycle it to the nearest bicycle shop (which is also quite far) because i only have one working brake on the bike now and it isn't the best one.

i did try to adjust the handlebar angle against the brake pinch by turning it right and then adjusting the cable to ensure there is no pinch but with that, once the handlebar is turned straight, there is no zero tension on cable and depressing the brake lever does nothing.

Have you lubricated the cable housing before threading in the cables?

they came lubricated but does lubrication causes the problem i'm facing?

not sure what witchcraft is happening.

Could be lubrication issue , or it could be the cable itself isn’t good quality. Are you using Jagwire?

i don't know what type of wires i was supplied with. this is my first bike and i wanted to try it out before really splurging.

but to me, this feels like a tension issue.

(1) when the handlebar is straight then all is well;
(2) when the handlebar is turned right, the length of the cable becomes short and it pulls the cable causing the unwanted braking;
(3) when the handlebar is turned left, the length of the cable extends and looses all tension in between.



i'm so dumfounded right now.

why is assembling a bicycle break cable so difficult 

What you are describing are symptoms of cable tension due to inside friction or bad cable quality. My advice is to spray some WD40 into the cable housing or perhaps change to better quality Jagwire cables.

spray the entire length of the cable or just a certain particular part?