Im currently having break problems with my g35s 2007 model I have replaced the master cylinder twice with brand new cylinders and each time I try to get it fixed up I take it out for a spin and I end up with locked breaks until I break lose the break line beside the master cylinder, is their a step I didn’t do or is this a separate issue I can’t figure it out

 

Sounds like the brake booster is sticking. This could be a internal valve failure or the pushrod might be out of adjustment/ sticking in the bore. If the brakes are only releasing when you release the brake fluid, then the booster is still applying the brakes (not releasing).

There were a few TSB's issued, for Nissan models, around 2008-2010, or so, for defective brake boosters. In some cases, once the brakes were applied they did not release. In others, you breathed on the brake pedal and it would slam you to a stop.