Ok folks. Need an opinion or 2.
I replaced all the brake lines on my delta because I found one with a small pinhole, and bled the system accordingly. Brakes have been great for a few weeks now. However, at the last few stoplights on the way home today the pedal started to slowly sink into the floor. By the time the light changes from red to green the car starts to inch forward. I checked the fluid level and both reservoirs were equally full. fluid level was about halfway up to the top. I checked the bleeders and they are all closed. By the time I get to the next light, the brakes work again, and when stopped, starts to slowly sink again.
Booster?, or master?

 

Is their any fluid leaking at the back of the master cylinder? Sometimes those like to leak after changing brake components. If not, their is some procedures in Haynes manuals to help diagnose this type of stuff, or if you have a factory service manual that would be your best bet.

 

Master and booster had no visible fluid. and the lines were dry as well. Is it possible for the booster to suck in fluid if the master cylinder seal has blow by?

 

I have never heard of that. You would at least have some type of indication of a vacuum leak. I think that a bad booster will give an extremely hard pedal, so maybe that will point you in the right direction.

 

SOUNDS LIKE THE SAME PROBLEM I HAD RECENTLY. IT WAS THE BOOSTER. I HAD TO HAVE IT REBUILT. CHRIS

 

I had a similar problem with my old silverado. Replaced the master and the problem went away.

 

Classic master cylinder symptom.

 

My 78 Delta did something similar after changing the rear wheel cylinders and bleeding the system. It ended up being the master cylinder.

 

Felix, it's the Master Cylinder...

(yes, I'm dating myself)

 

Good thing I have 4 extras from all my old deltas

 

Get prices before you decide. I was AMAZED at how inexpensive a new one is. I believe the last time I needed a kit for the master cylinder on one of my Deltas, it was a little over the cost of a whole new master cylinder.

 

Will do. Thanks again.