4 wheel discs: What combination are you running?

[Kern Dog]

I really need to improve the brakes in this car!
I'm running the Cordoba 12" front rotors with single piston 2.75" sliding calipers. The rear is the Dr Diff disc kit with 10.7" Toyota based rotors, 1.5" single piston Mustang based calipers. I have a 75 Dart power booster with a 15/16" master cylinder. The engine makes low idle vacuum so I added a vacuum storage tank, but it still isn't enough. High speed braking is great but at lower speeds, the brakes just are not nearly good enough. I have looked at using an electric vacuum pump but the new kits are often $260 and up.
In 2012 I tried switching to a non power (manual) master cylinder. I tried 4 different ones, all with different bore sizes ranging from 15/16" to 1 1/8". None of them worked well either. Each one was capable of developing a firm pedal but none of them gave adequate braking. In fact, the braking was so bad, I was barely able to get the tires to skid on gravel! I really like the light weight and simplicity of a manual brake system and would prefer to go that route but with the luck I had, I really would benefit from seeing what other setups that other guys have used.

 

[5.7 hemi]

A 7/8 mc will knock the filling loose in your teeth if ya go all manual disc.

 

[71charger_fan]

I'm running pretty much the exact same combo you are only with Volare front disks. I've got a Dart manual disk master and it stops great.

 

[razreddobie]

Are you using a disc brake master and what kind of distribution valve?

 

[benno440]

if you have the coin why not run a hydroboost system, do you have power steering? if not then you cannot use one and you are stuck with vacuum lol

 

[71charger_fan]

I'm running a Raybestos MC36406 master cylinder and a combination valve scavenged from either a '73 Charger or a '77 Volare 4 door. I've forgotten which combination valve I used. I think it's the Charger one.

 

[Greg Ducato]

Have you checked pedal ratio? That is critical when switching from power to manual brakes

 

[Kern Dog]

Have you checked pedal ratio? That is critical when switching from power to manual brakes

The car came with 4 wheel drums originally. Currently the booster and master cylinder are OEM for a 75 Dart disc/drum. The setup has its own built in offset/crossbar linkage to reduce the pedal ratio. The manual ratio is close to 6.5 to one when I crunched the numbers before. Not sure what the power ratio is.
If I pop it into neutral and rev it to 2500 or above, the car stops great. I'm sure it just needs more vacuum to make the booster work. 4-5" of idle vacuum in gear isn't enough. An electric vacuum pump may be the simplest solution.
A guy on another site thinks that my 2.75 single piston front calipers may be too large for a manual master cylinder. he suggested a switch to Viper calipers. Their 4 pistons supposedly have less square inches of piston area.

 

[71charger_fan]

Mine was originally a 4-wheel manual drum car, which seemed odd for an SE.

 

[Kern Dog]

PROBLEM SOLVED !!

Today a friend from our local Mopar club gave me a vacuum pump that was from a late 80s Cadillac. I pulled out the vacuum tank I had that was basically worthless and bolted in the pump. It is wired to be ON when the ignition is on. I finally have "Brake Dive" for the first time in years. Tomorrow I'll have it on the road for a better test but I suspect that it will be great.