I can't stop the bleeding!!!

[Danny Gutierrez]

First of all, thanks in advance for all the help you guys have given me over the years.  I truly receive more from this site than I give.  I seem to have a slight problem with my brakes.  I have to constantly bleed them all the time.  For instance, I will gravity bleed my rear wheels and the pedal is nice and firm.  I'll drive the car for a day or so and the pedal gradually goes soft.  I'll then bleed and the pedal is firm again.  I'm NOT losing fluid anywhere, yet there is always a small amount of air in my system every time I bleed.  I have a manual disc/drum combo on my car.   

[Just 6T9 CHGR]

You might not have a visible leak buuut you might have a hariline crack in a hard line (or rubber) that is letting air in.

Go over all your rear lines with a mag glass

[Silver R/T]

maybe master cylinder is bad?

[resq302]

How is the master cylinder cap gasket?  I had a friend of mine have a similar problem in his 68 Camaro and it turned out that his master cylinder cap gasket was bad.

[1970dodgecharger]

Do you have any joints in the lines?  Connectors...  I had this once where no fluid was leaking but it would draw a tiny bit of air until I discovered it and tightened the hell out of it.  Give it a try.  AL

[Back N Black]

If your only gravity bleeding, that may be the problem? It will take a long time to get the air out with just a gravity bleed. Get a buddy to pump them up and apply pressure and crack the line, repeat until all the air is out.That may solve the problem.

[is_it_EVER_done?]

Danny: If you're not leaking any fluid, you probably don't have a residual pressure valve in the rear brake portion of the master cylinder. The residual pressure valve was designed/used specifically to stop the system from pulling air in past the drum brake cylinder seals by allways keeping a few pounds of positive fluid pressure in the cylinders.

At some point in the mid 70's, the rear drum cylinders were redesigned to include a spring inside that kept a bit of fluid pressure on the pistons, and the residual valve at the master cylinder was discontinued, so if you have ever replaced the M/C, you probably got one without the residual valve.

In any event, you need one version or the other in order to keep a bit of pressure in the drum portion or else it pulls air in without leaking fluid.

[Chryco Psycho]

Wilwood makes an inline  residual pressure valve

[mikepmcs]

http://www.wilwood.com/Products/006-MasterCylinders/010-RPV/index.asp

http://store.summitracing.com/egnsearch.asp?N=700+400196+115+1002


you would want the 10#  one if this is, in fact, a possible solution to your problem.  the 2# one is for the front discs.

v/r
Mike

[Danny Gutierrez]

Thanks for all the help guys!!  I have replaced the master cylinder in the recent past.  I was looking into one of those "newer" style master cylinders from Mancini racing.  Problem is they have two versions and I don't know which one to get.  Anyone try any of these?