New brakes,pedal on the floor..

No the booster doesnt work that way. It is spring loaded toward your pedal so it should hold your pedal up regardless. The boosters have a diaphragm inside with the front half being the vacuum side. when you hit the brake pedal then vacuum assists you by pulling that diaphragm forward pushing on the master cyl rod. Is this unit made for your car? If not your guess on rod length is probably pretty close. Is it a power brake master cylinder? Try bleading your system first though to see if that helps though its doubtful.

fastdave said:

I am building a 67 stang. I put in a power brake booster. The brake pedal is only about 1 or 2 " from the floor.It should be a little over 5". When I finish it and start it up will the vacuum in the booster push the pedal to the normal position or do I need to get a different length rod or something else?

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Did your car originally have power brakes? If you are changing from manual to power brakes with a new booster, you need a new pedal and you have to relocate its mounting position on the bracket. The pedal will have a different mounting point on the bracket. You cannot fit it on the same spot as where the manual pedal mounted. You have to take the mounting bracket off. You will see a pre-marked spot on the bracket about 2 inches on top of where your original pedal mounted. Drill a hole through that and mount your pedal there.

have a look at the picture on page 4 of this link to show the new mounting position.

http://www.911brakes.com/bm1521installpdf.htm

good luck.