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Brakes booster 101

jump in truck this morning.starting driving got to stop sign and hit brakes the brake pedal was hard as a rock so i’am guessing brake booster right or brake booster check valve.

depending on your vehicles set up (sorry, i’m not very familiar with Nissan’s,) this could be a vacuum leak or a p/s fluid leak (depending if your booster is vacuum operated or hydraulic.)

or, as you said- a booster or check valve.

That would be my guess too.
Try this: with the engine off, pump the brake pedal until it becomes hard. Then, while pressing on the brakes, start the engine. The pedal should sink a bit and get a softer feel. If it stays hard, your booster is bad or the check valve in the vacuum line is stuck closed.