[mhb292]

I have a 65 stock drum non power breaks i have replaced shoes and drum pistons. i think my master cylinder is going bad, when i have the car in drive and hold the break down it slowly loses preasure and the pedal will slowly move to the floor please help me

[basketcase]

The brake system is sealed so I would first check for leaks. Did you check the fluid level in the master cylinder after the breaks went soft?

[Bob A]

Like Basketcase said check the brake fuild level if it's low you have a leak. If not yes it's your master cylinder bypassing internally.

[RagHead]

If your fluid level in the master cylinder is low check each one of the wheel cylinders, one or more of them may be leaking. If the fluid level checks out ok and no leaks, replace the master cylinder.

[basketcase]

Another problem could be air in the brake lines. You bleed the lines from the passenger side rear to the driverside rear to the passenger side front to the driverside front. iow from the furthest cylinder from the master cylinder to the closest. If they all check out and there is no air in the lines it's time for a new master.

[mhb292]

no there are no leaks when i changed shoes and pistions i replaced all the break lines

[basketcase]

If you bled the lines properly then its the master. I suspect that you do have some air in the lines since you replaced them. Remember you can't compress a liquid. Thats why your hyrdralic (liquid) brakes work. if there is any air in the lines you'll be compressing that.

[jay67fast]

I'd say slide under that puppy and check again for leaks. It's too much of a coincidence that this problem started right after you worked on the brakes.
If you check the entire system (Wheel Cylinders, the whole length of the brake lines, the master cylinder fittings and distribution valve fittings) and there no leaks, the next thing is to re-bleed the brakes so you're SURE there's no air in the lines.If all that fails to locate the problem then you're down to the master cylinder. It's not inconceivable that the M/C is bypassing fluid, in that case your fluid level will remain stationary, but it seems to me to be more likely that something is leaking, particularly if your fluid level is dropping.
Hope that helps,
Jay67fast