hey guys whats up.
my brakes started to go out about two months ago (the pedal would go to the floor and I would haft to pump them to get them to work). so I replaced the brake master cylinder, and then they worked fine. now two months or so later it seems that it is starting to go out again because if it sits for some time, (like overnight or eight or so hours I have to pump it once and then they work fine until the next time it sits). does this sound like the new master cylinder is going bad or is it something else. it does not seem to be leaking any fluid, I just checked it for the first time sense changing the cylinder, and it looks like the same amount. it has manual brakes.

Thanks for any help.
1974 T-top 350cc.

 

Our C3 corvettes are notorious for bad brakes, mainly because the cars sit so much. The brake calipers are usually suspect, rust causes them to leak.
Did you "Bench bleed" the master cylinder before installing it?

Check the entire system for leaks, repair as needed and bleed the system to get air out of the lines.

 

yeah I bench bleed the master cylinder, it took me about a half an hour but I know I got all the air out of it. I geuss I'll just have to bleed the whole system again. I would not think that my calipers have any rust on them though because I drive my vette alot. also I have another question that is a little off topic but is the side marker lense made to come off? The one on my driver side rear fell off somewhere, and all I can find online to replace it is to buy the whole assembly.

 

The side marker lense is glued in and not sold separately. One of mine fell off just out of warranty.

If when you bench bled the M/C, you bottomed out the piston, you may have ruined the seals as some aftermarket units do not have a finished bore all the way to the end.