Handbrake Doesnt work on rear caliper Help!

hello my mk1 had a rear disc conversion when i brought it, i was getting it ready for an mot n realise the handbrake doesnt work when applied on the rear nearside caliper but it work when i use the brake pedal.

is this a fixable problem? if so how can i fix this?

Cheers

whip the caliper off and pump the handbrake lever while you watch the piston. if it doesnt move, you need another caliper. this can be casued if you try to compress the piston using a vice or gclamp without also twisting it, ideally buy yourself a proper windback too like this:
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