My brakes have suddenly become much harder! The pedal is very hard with the engine off (after pumping to remove the vacuum), then it drops a bit with the engine on and assistance from the servo but the brakes feel considerably harder than before? Is it possible that the Servo's on its way out? I replaced the brake shoes about 6 weeks ago so it maybe down to them self-adjusting with wear leading to harder feeling brakes?...

which car?

Servo sounds fine, have you checked the fronts? Calliper slider pins moving freely? rear adjusters stuck?

Volvo 340DL 1.4 1988

I checked the rear adjusters today and they're moving ok although the offside one isnt as rigid in its slot ie;its moving from left to right inside the hole it sits in and doesnt appear to be able to self adjust as its not coming into contact with the fixed serated small drum/disc! Why would this be as the spring below it is in place?...

I had a similar problem with my 340 recently.

What had happened is that the vacuum take off pipe for the servo had collapsed internally.

There is basically a small section of flexible rubber hose at the end of pipe which connects to the manifold. Have a check of that and make sure it's clear.

Hope that helps.