Hi, I recently noticed the brake pedal in my 1970 starting to fall slightly to the floor.   This causes the brake lights to come on and if I don't pay attention may cause a dead battery.   I checked the reservoirs in the master cylinder and noticed the brake fluid level was down a bit.  Someone told me that the seals in the master cylinder are leaking causing low pressure and the pedal to fall to the floor.

Is replacing the master cylinder straight forward?  Are there any gotchas?

If your level is going down in the reservoir, you most likely have a leak somewhere, check all calipers and connections.

Changing the master brake cylinder is fairly easy. It is important to get all of the trapped air bubbles out of the system. Generally recommended to bench bleed the master cylinder in a vise before installing in the car. This way you get all of the air out quickly and the air does not have to clear all the way through your brake lines. When changing your master cylinder it is a good time to flush the brake lines completely with new fluid. And while you are at it, change the rubber hose that connects from the caliper to hard brake line near each tire. There are some good historical threads on bleeding the brakes, just do a search. Good luck.

Excellent!  Thanks for the info. 

i JUST WENT THROUGH THIS WITH MY VETTE, ALL I DID WAS TAKE IT TO LES SCHWAB TIRE AND HAD THEM DO A COMPLETE FLUSH AND REPLACEMENT, NEVER NOTICED ANY SIGNS OF LEAKING AT THE WHEELS AND THINGS SEEM TO BE VERY GOOD, LESS THAN 30.00 DOLLARS......

L