Correct

掉链子

/ diào liànzi / 
Strokes

Definition

one's bicycle chain comes off/(fig.) to let sb down/to drop the ball/to screw up

Example

As a Verb

(of a bicycle chain) come off

1
Wǒ
我
de
的
zìxíngchē
自行车
lǎo
老
diào
掉
liànzi
链子
  
。

My bike chain keeps coming off while riding.

As a Verb

go wrong (usu at a critical moment); drop the ball

2
Zhè
这
jiàn
件
shì
事
shàng
上
wǒmen
我们
kě
可
bu
不
néng
能
diào
掉
liànzi
链子
  
。

Let's not drop the ball on this.