I just replaced the master cyl on my 93 civic EX about a month ago. I bled the brakes while I was at it. Now it's leaking brake fluid somewhere. At first, a while back, I topped off the master cylinder. No big deal, must have finally settled. Now all this time later it's down about 1cm. So I topped it off again and checked all four bleed screws and the lines that go into the calipers and rear cyl's. Completely dry. The hoses look good too. Also, the lines that go into the master cyl are dry too. Is it air that's just coming out of the master cyl?

I did bench bleed the master cyl thoroughly before I installed it.

 

look on the inside of each rim is any of them wet?

 

Look under the dash, where the master cylinder piston comes through the firewall.

 

there's no fluid to be noticed where the brake thing pushes through the firewall. The brake system works just fine too.... Hmmm.

 

and there's no way the rims could be wet, the inside of the backing plate on the rears are dry/no fluid on bottom and the front wheels have been off recently and were dry as a bone

 

Check the rubber brake lines at each corner of the car

Do you have rear drums or rear discs?

 

I have checked all of those too. I have rear drums.

 

park the car on a clean drive way in the same spot each time after driving it and then if any leaks you will be able to idenify where its coming from

 

Unbolt the master cylinder from the booster and look for leaks out of the back of the cylinder. I think you can do this without disconnecting the lines. If brake fluid has gotten into the booster it will ruin it, need to replace both the master cylinder and booster.

If you have ABS it could be the ABS box, I think a leak would be apparent to the outside. Also if the front pads are wearing out very rapidly, the fluid level will drop as the pads wear even though there is no leak.

Also a metal line could have rusted out, particularly the long ones that go under the car to the back.

 

Also check your proportioning valve. It has 6 lines or so going into it. I recently did a rear disc brake swap and my 4040 prop valve started leaking around one of the fittings.