rear brakes won't bleed?

[Flanders 46]

Just finished front disc brake swap.

I bled the fronts first (gravity bled) and attempted to bleed the rears, but no fluid was coming out whatsoever.

Ultimately I disconnected the fitting on the master cylinder that goes to the bowl for the rear lines, and no fluid dripped out at all!  Could the master cylinder be clogged somehow?  I bench bled it before I installed it and I got all the bubbles out, but would a bad bench bleeding job cause this?  I'm perplexed as to why no fluid came out when I disconnected the fitting on the side of the full-of-fluid master cylinder.

 

[1969_Mach1 333]

If I remember there is a residual check valve in the master cylinder port for the rear drum brakes.  The residual check valve maintains a very small amount of fluid pressure against the lip seals in the drum brake wheel cylinders.  Try bleeding the rear brakes with a vacuum pump or pressure bleed them with the help of somebody pushing on the brake pedal.  I use this.

https://www.matcotools.com/catalog/product/MVP5000/VACUUM-PRESSURE-PUMP/#to-details

They are made by Mighty Vac.  Mighty Vac has lower cost all plastic versions of it, about $40.  It's not the quickest method but works good, doesn't make a mess, and with it you can bleed brakes by yourself.

There are low cost pressure bleeder tanks that connect to the master cylinder.  Don't use one.  The low cost models are a simple pressurized tank and do not separate the air from the brake fluid.  This is bad for the brake fluid.  Expensive models have two chambers with a rubber bladder separating them to isolate the brake fluid from the air.

[Brian Conway 264]

I think your on the right track.. Should have been some leakage/seepage at the MC and from the rear brake line.   So, I guess, next you will be stepping on the brake pedal to see if anything squirts out of the empty fitting?    Easy does it and stick a towel in there.  Brake fluid eats paint.  Brian

[Flanders 46]

5 hours ago, Brian Conway said:

I think your on the right track.. Should have been some leakage/seepage at the MC and from the rear brake line.   So, I guess, next you will be stepping on the brake pedal to see if anything squirts out of the empty fitting?    Easy does it and stick a towel in there.  Brake fluid eats paint.  Brian

ya, nothing squirted out when I put the pedal down :D  I'll pull the MC on the weekend and see what's up!

[Caseyrhe 650]

What ended up being the fix

[danno 128]

I just installed a new master, and bench bled it. The front was pumping right away, but the back took a lot of pumping before fluid started flowing.  I am not sure why. Once installed, I could see fluid coming from the rear bleed screw.    You might want to try the bench bleed.