poor braking (87 2wd)

[p7387]

87 2wd
i noticed it was getting slightly more difficult to break, having to apply more pressure and not feeling that firm grab but rather more of a sliding sensation. upon inspection i noticed the smaller front reservoir was almost empty. i looked at the line connections around all wheels and did not see any evidence of leaking.  i took a quick look under but did not see anything apparent.

the lines are original and i know they will need to be changed at some point. i did a complete front brake job 18 months ago and all was fine. its the small reservoir that's low, the larger one is fine. is that smaller reservoir dedicated to just the front or back?

any ideas would be appreciated

thanks

[bake74]

     Has the master ever been rebuilt ?  You might need to rebuilt or replaced.

[Blazin]

Smaller reservoir is usually for the rear brakes. It could be leaking out the back of the master into the vacuum booster.

[p7387]

i think the master is original
i will fill the reservoir and keep an eye on what happens, but shouldn't i notice fluid leaking from someplace if it is the master?

[79gmc15]

What does your brake booster look like under the m/c? Is it wet? Rusty?

[p7387]

ill take a look and report