hard pedal doesn't stop after front disc swap

[TN Mopar]

66 Dodge Charger with a 440 manual brakes

years ago I swapped my front drums to a disc brake set up from a 73 Duster
I used a new master new discs, new calipers new lines
the car sat for 10 years (closed up without fluid in it) and I finally put the system back together
I recently swapped to FMJ calipers because I wanted rear hung calipers to keep the factory sway bar

The problem is I have a hard pedal but the car doesnt stop well
You can't lock them up

Secondly the dang Master leaks fluid out the top so I want to replace it

Is the Master the problem here?
and if so is there a Master cylinder that works better

 

[BeepBeepRR]

Have you bled all four corners starting with passenger rear then driver rear? Also did you bleed the master cylinder?

 

[TN Mopar]

yes more than once
pedal is rock hard

 

[Beekeeper]

what bore size MC did you install?

 

[TN Mopar]

I do not know what size is on it
What ever the parts store gave me for a 73 duster 10 years ago
I am wondering if I need to go to 15/16 bore

 

[Beekeeper]

that’s what i was gonna recommend the smaller bore would have more power with a little more travel

 

[TN Mopar]

I need to replace the master anyway
its leaking out the top and making a mess of my paint

 

[66Satellite47]

From what I can tell, the MC bore, pedal linkage adjustment, and proportioning valve all need to be a correct combination. I'm told the proportioning valve can go over center, needing a re-set. Good luck.

 

[tonysrt]

How are you bleeding the brakes? Someone pumping the pedal or a vacuum pump? If someone pumping the pedal should be able to go the floor with it. Also could be that the M/C plunger has dried out since it was left so long dry.

 

[Frank Mopar]

Take the guess work out and pick yourself up a brake pressure gauge so you know exactly whats going on.

 

[TN Mopar]

I bled it first with 2 people and pumping
Second time I used a vacuum pump

I suspect the master cylinder is the problem and I have ordered a new 15/16ths bore Right Stuff Master from Summit

 

[steve from staten island]

I bled it first with 2 people and pumping
Second time I used a vacuum pump

I suspect the master cylinder is the problem and I have ordered a new 15/16ths bore Right Stuff Master from Summit

Please keep us informed as to how things go

 

[TN Mopar]

Please keep us informed as to how things go

I will
I have the new Master in and will put it in the car Sunday

 

[moparnation74]

The Master cylinder is the root cause.....

 

[TN Mopar]

We put the new master cylinder from Summit in the car today
(Right Stuff Detailing Master Cylinder G1501 - 15/16 bore)

Brakes are much better!
Pedal is softer with more pedal travel and I can lock up the brakes in a panic stop and in a hard stop she stops very quickly
The car is much safer to drive

 

[moparnation74]

We put the new master cylinder from Summit in the car today
(Right Stuff Detailing Master Cylinder G1501 - 15/16 bore)

Brakes are much better!
Pedal is softer with more pedal travel and I can lock up the brakes in a panic stop and in a hard stop she stops very quickly
The car is much safer to drive

Thanks for the update......I thought that was the root cause.....

Glad to hear it is safe to drive and back on the road!

 

[Joe66satellite]

Maybe while this thread is still fresh, I can get a little help here. I ve got a 66 satellite Factory power Power Drum / Drum car. The previous owner installed a 440 with maybe 15 inches of vacuum and left the power booster on an installed the ssbc a156 front disc brake kit from Summit
With the MC that came with the kit didn't install a proportioning valve I had a hard pedal zero travel nearly and terrible brakes oh, I install a proportioning valve and they're a little better but I'm thinking of converting to a manual 15/16 bore master cylinder as mentioned in this post or maybe I could just get a 15/16 bore master cylinder and still use that older booster which is still working God knows I don't want to go under that dashboard to take that thing off oh, any help please, Buehler?

 

[1 Wild R/T]

Are you sure the booster is working? Try this.. Engine off, step on the brake pedal 3-4 times... Then step on it & keep your foot on it with light pressure... Start the engine.. Did the pedal fall slightly? If not the booster is bad... If it did chances are your gonna need a smaller diameter master cylinder to compensate for the booster being designed for drum brakes it doesn't have as much assist as a disc brake booster...

As was mentioned earlier a pressure gauge would be useful in gathering accurate info to diagnose your issue..

 

[Joe66satellite]

Thank you one wild RT I already tested the booster and it is working I'll get a gauge to read the pressure at the calipers next ,I also just wondered if I could keep the original style drum booster on there and would it still be compatible with a smaller diameter bore master cylinder?

 

[1 Wild R/T]

Yes...