Brake fluid flowing back into master cylinder

[rab]

1983 ranger that had manual brakes that i swapped to power brakes.
So heres how i did the swap...
87 power pedal cage
90 brake booster
90 master cylinder
95-up dual piston front calipers
stock 83 ranger rear drums
stock 83 proportioning valve

Also when i did this swap i had to use some brake line adapters at the m/c to adapt to the stock 83 brake line fittings.

So whats happening is i can not bleed this brakes, fluid is flowing back into the master cylinder when i pump the pedal, that must be causing it to keep adding air to the system.
I bought a brand new master cylinder when did the swap and yesterday rebuild the used one i had, both of them are doing the same thing, i.e. fluid is rushing back into the m/c...
i bench bleed both m/c's before installing and spend hrs trying to bleed the brakes after installing each of the m/c's, also when i bleed them on the bench there is no back flow. also each bleeder screw has plenty of pressure so nothing is really backed up.

So I'm running out of ideas on what else could cause the fluid to back flow back into the m/c.
maybe the proportioning valve needs to be swapped?, any ideas or input would be greatly appreciated.?.?

 

[RonD]

Only way I can see fluid flowing back would be thru proportioning valve.

 

[rab]

The bias/ratio with the stock proportioning valve should be fine with the set-up i have? or did this need to get swapped also?
Im thinking about pulling the stock one anyway to see how it looks.

 

[alwaysFlOoReD]

Isn't there some residual pressure check valves somewhere?

 

[Bird76Mojo]

I wish these threads had a conclusion. ugh

 

[Uncle Gump]

I don't believe there would be any way brake fluid can do that. What I do know about master cylinders is that they will allow more fluid into the bore then it will need for the next brake activation. I believe it's called a compensating port. The excess fluid will be expelled back into the reservoir. Have someone pump the pedal without the cap being on and you will see the brake fluid swirl.... it may even squirt out into the engine compartment.

A residual valve in my experience is a one way valve that will hold brake fluid pressure... very small amounts...2 or 3 psi on the system south of the master. If that valves one way functionality failed it would most likely result in a lower pedal. There are many brake system that don't use them and they don't send fluid back to the master so I doubt that was his issue. I have installed them in several dune buggies when equipped with a steering brake... It was the only way to get a good feel on the hand operated steering brake. If the vehicle does have a residual check valve it is typically housed within the proportioning valve.

Bird... Are you having some issues with your beam/brake swap?

 

[Bird76Mojo]

I shouldn't have dredged up an old thread but it's frustrating when these threads never reach a conclusion.

I'm just trying to research the power brake swap ahead of time, just in case my 95-97 beam/brake swap on my manual brake 87 leaves me with less than stellar brakes. It's still a work in progress. The constant rain has stopped my progress for now.. I'm waiting to do some media blasting but I refuse to do it outside in the mud, and the extra humidity in the air certainly won't help my homemade pressure pot blaster any.

 

[Dirtman]

I always assume when threads like this never reach a conclusion it's because the OP finds they did something silly to cause the issue and doesn't want to admit to it in public.