Dual Master feeling hard?

[4gotn1]

I have a dual master cylinder on my car. Normally when pop a line and then the secondary picks up, is the pedal hard after that? My pedal is really hard now with very little braking and there is hardly any juice going to the fronts. I have turned the prop valve all the way down so I can get as much up front as possible but only the backs are working. Any help? Should I replace the master cylinder?

[DrJ]

Say Waaaah???

"Pop a line?"

What you talkin' boy? http://www.jalopyjournal.com/ubbthreads/images/graemlins/confused.gif

[yorgatron]

the proportioning valve,if it's an OEM type,will have a button-type gizmo you have to push on,it's a safety valve thing.i don't have a picture,but i had to do it on my van whenm i replaced a bad M/C.

[tommy]

You'd get a lot more inteligent reponses if you told us what kind of car, what components if it's a rod, power assist?, sequence of events that got you to this point. etc. etc.

[50dodge4x4]

The factory proportioning valve has a block off valve (pure tech terms used here http://www.jalopyjournal.com/ubbthreads/images/graemlins/grin.gif) in them that would block off fluid flow to what ever side lost the ability to hold pressure. It is a built in safty feature. If you stomped on the brakes and, say, blew a front brake hose, the block off valve would go past center and block off fluid flow to the front brakes. To get the fluid flow back to the front, you have to recenter the block off valve. To do this you need to open a bleader screw on the rear and step on the pedel (with force) until you center the valve. You will hear it click back to center, as soon as it clicke, close the bleader and quit pushing on the pedel. It is real easy to go over center and block off the rear brakes. Once the valve is centered, you can blead the brakes in the normal way. I've seen it happen when people were bleading brakes too. All you have to do is apply hard pressure when either fromt or rear bleaders are open and the other ones are not. Front wheel drives can do this too, but their brakes are set up with one front and the opisite rear teamed up. I encounterd this way back in the early 70s when I was helping my boss blead brakes on a car. He knew what he had to do. Sorry so long, Gene

[4gotn1]

55 desoto running stock drums in the front with 15/16 wheel cylinders (2 per wheel), 71 challenger rear with 10 in drums with 15/16 wheel cylinder, Adjustable prop valve, 10 lb residual valves both front and rear, master cylinder from a 92 Caravan that is somewhere close to an inch bore, and a booster from an 82 dodge ramcharger. The booster is working and I have good vacuum. Pedal has always been hard. I started with a 1 1/8 bore MC from the truck I stole the booster from and same deal. Hood clearance was a problem so I went to the caravan unit. Yes I adjusted the push rod so it should be close if not right. Everything is new except the booster and worked when I pulled it off. I just want to see if maybe when I bench bled it maybe I pushed it to far in. I don't know at this point. I have a disc brake kit for it but I want to solve this first so I don't fight to things at once. Thanks

[Model A Vette]

The caravan MC is designed for front disk & rear drum. That may be a problem but I doubt it.
Did you install the above mentioned block with the switch that tells you that you lost part of your brakes? Sometimes they have a part built into them or the MC that holds off the front brakes until the rears start to work. That would be in a disk/drum system. Sometimes there are also proportioning valves built into the blocks.