the rear wheel cyl would be were l,d look / it,s the only place that will leak real slow

 

I have also seen the power brake booster diaphram rupture and the fluid gets sucked by the manifold vacuum into the engine and get burned. This usually makes some pretty obvious blue'ish smokey exhaust while drinking the master cylinder dry. Have to have power brakes! And have you noticed any smoking lately?

 

the rear wheel cyl would be were l,d look / it,s the only place that will leak real slow

You may have to remove the drums to see any leaks.

 

Well, no blueish smoke, so I guess its time to pull some drums. Anything quirks to gettin the drums off?

 

Mine have always come right off with just a little persuasion. However, you can access the adjuster wheel through the access holes in the backing plate and retract the shoes if they are keeping the drum on.

 

cool, thanks fo rthe help!

 

retract the shoes and IF its still a pain or rusted at the axle hub deal a 5# sledge will get em off! i know that from experiance... my PW when i first got it......

 

it's the rear seal in the master cylinder .i had the same problem in my 77 .easy fix

 

If the system is not visibly leaking fluid, the problem will be internal in the master cylinder. Its called pedal fade. The primary cup seals are shot and fluid is just bypassing into the master cylinder reservoir.
Also, If there are no leaks, check the front brakes. As the brake pads wear, the caliper pistons push out farther to adjust for thin pads, when you install new pads the fluid will be pushed back into the master cylinder