If the booster is not working the brakes would feel like they would if the engine is not running - no vacuum assistance - so they would work but you'd be standing on the pedal to the point you thought you were about to snap it. This would be to varying degrees if it only has a vac leak.
To check, take the vac line off from alt or front pump (depending on your model) or from manifold if petrol, if that makes no difference then it's a vacuum issue, whether booster leak or vacuum source.
yer cheers Leethal for your reply . break pedal has a real dead wooden feel to it, it can be a bit scare trying to stop in a hurry some times especially if towing a trailer with a bit of weight in it i have taken the vacuum hose off the booster and there is a fair bit of suction going on there enough to suck your finger to the hose. i have swapped the alt over from another gq i have but brakes still no better.is the booster serviceable or is it a throw away job