The brake booster on my 1978 FJ40 works sometimes and sometimes it does not. In other words, sometimes it feels like I have power brakes and then again it feels like they are completely manual and I have to push the brake pedal real hard to slow my cruiser down. Short of removing, replacing, rebuilding, etc.., is there anything that I can try to do to make it work better. I am getting good vacuum to the booster from my intake manifold. Any advice would be appreciated.