One side broken ? Do i need to replace both ?

Your balance shoe is the 15-180 Coil Balance Shoe. To determine if this is the correct replacement match, carefully review and compare the dimensions below.

Alternate image for 15-180

The compatible coil spring is the Series 190 Coil Balance, which is attached to the shoe using the 33-073 screw. They are anchored to the window track using the 15-186 Coil Balance Clip.

To determine the correct coil spring, you'll need to look for a stamp/marking on the coils. If there are none, take a look at the video tutorial (tagged below) for instructions on selecting the correct coil weight option.