1969 Dodge Charger air in brake lines

[nickm]

   Hey guys, I just picked up my first '69 Dodge Charger so go easy on me 

I believe the hydraulic safety switch disabled part of the system due to hydraulic failure.  I have the red light on the dash, and the brakes can't hold the car when you put it in drive.

I replaced the master brake cylinder (manual drum/drum) and did a bench bleed using a bleeder kit.  While trying to vacuum bleed the rear brake lines, I'm unable to hold vacuum (5-7lbs) longer than a few seconds.  The fluid that I am able to pull from the lines is full of air, but I don't have any visible leaks.  The peddle is solid with the MC plugged, and has normal travel when connected to the lines.

Any ideas on next steps?  Do I need to ditch the vacuum bleeder and just do it the old fashion way with pumping the brakes?  I've read a few posts about gravity bleeding the lines, should I give that shot?  Is there a distribution valve somewhere in the rear that maybe letting air in, but not leaking fluid?

I do have plans on replacing the manual drum/drum system in favor of a more performant braking system, but I have a bit of laundry list in front of upgrades right now.

Thanks for the help! 

[BLK 68 R/T]

Congratulations on your new Charger and welcome to the site.

There are 7 potential spots on the rear lines that you could be getting air. On the rear axle there is a brass brake line tee. 2 hard lines run out to each wheel cylinder from it (4 potential leak spots) . Connected to it is a rubber flex line (2 potential leak spots) that connects to the hard line coming from the front proportional valve ( 1 potential leak spot). If the rubber line is old it may have cracks in it that are letting air in. Are you starting with the right rear line, left rear, right front and finally left front line when you are trying to bleed the system? also make sure you are not sucking all the fluid from the master cylinder reservoir. Me, personally, have always like the traditional way with another person pumping the pedal.

[nickm]

Hello BLK 68 R/T, thank you for the reply. 

Yes, I'm bleeding in the correct order, working my way from the furthest point.  I also have a second person checking the fluid level in the mc to make sure I don't pull air back into the lines.

I will check those 7 potential spots as soon as I get home.

Can a bad wheel cylinder leak air?

Thanks!

[BLK 68 R/T]

You're welcome.

Yes, a wheel cylinder with defective/worn seals could cause air to get into the system.