I think that I want better brakes........

[Kern Dog]

Mine work fine but after driving late model cars, I want what they are having!

The Charger affectionally known as Ginger....

The current setup is the 1975 A body knuckles, 12" Cordoba discs with a 2.75" F-M-J body iron caliper, a 10.7" rear disc with a 1.5" single piston caliper and a 1975 Dart power booster and disc/drum master cylinder. Drum/drum distribution block. It fits, it works but it could be better. When I changed to the 5 speed earlier this year, the brake pedal had to be changed. I had modified the old pedal with the pushrod hole up higher; this resulted in a more favorable pedal ratio. Now there is a slightly greater amount of free travel before the brakes start to bite.
I don't know if a bigger set of rotors and calipers would make the difference. It isn't as if I am overheating the brakes from hard use. I don't think that I have ever had brake fade with this car with this setup. I have heard suggestions that old brake hoses can bulge out under pressure. This "lost motion" would result in the calipers "seeing" a delay in pressure or even some reduction of it.

My brake hoses were replaced about 5 years ago so they should be fine. I'll check though.
I remember reading an article in Hot Rod or Car Craft many moons ago about a car that had what they called a "Quick take up" master cylinder. I have never heard of that since then.
In short, I'm wondering if there is some type of master cylinder, power or otherwise, that reacts faster than what I have. The pedal has more free play than before but when it starts to bite, it works. The pedal never gets near the floor. It never feels spongy either.
My system has no leaks. The car stops fine, it just used to stop better. I know that the disc/drum master cylinder sounds like a mismatch but it worked quite well before the pedal swap. I could pull the pedal and modify it like I did with the automatic pedal but I'm curious if there is something available that feels more like a modern car.
In 2012, I wanted to switch to a manual master cylinder. I had 4 to choose from, with three different bore sizes and all of them resulted in a similar fashion: Hard pedal and poor stopping force. I like the idea of a manual braking system for the weight savings and for the less cluttered look. I'd try that again if I could be reassured that I could make it work.

 

[1STMP]

A dual diaphragm booster may help as they're
designed for 4 disc braking systems, and
contribute more to brake assist, and compensate
for lower than normal vacuum. Please bear in mind
that this is just my opinion, and many here
would disagree or dispute this.
I use one and have no problems.

 

[4mulas]

Smaller bore diameter master cylinder will give you more clamping force. I run a manual 15/16 aluminum master from dr. Diff and am happy with it.

On an aside, how do you check/add air into those tires? Is there more room than it looks like on the valve stem?

 

[Mopar Hunter]

What size master cylinder bore do you have?

 

[66 Sat]

Switch to drums all round. Some members swear by 'em....

 

[BeepBeepRR]

Found this bit of information maybe it will help.

Insert name here, are you wondering what applications use a flat, horizontally mounted QT MC as opposed to the bajillion GM cars that came with the diagonally upward mounted ones? There are a few that I can think of being used in flat applications...even though the only thing different about the diagonal ones is the reservoir angle.

The GM QT MC that I happen to be most familiar with is off of the S-10 PU/Blazer from 1983-1990. Both MC's used for power or non-power brakes were stepped bores but varied slightly from each other in the diameter of the larger bore. I'm currently looking for one that has screw on caps though, as opposed to the snap down variety. I know that Dorman makes replacement reservoirs, but I'm still waiting for my catalog...8-10 weeks my ***.

w/ PB - ACDelco #18M310: 24mm x 36mm
w/o PB - ACDelco #18M309: 24mm x 31.75mm (and was used on 1982 w/ PB)

In my experience, the 18M310 seems to work better with 4-wheel discs in my opinion because it moves more fluid but is still capable of generating the ~1000psi pressures that the calipers like to see to work properly. Peddle effort can get to be a bit excessive if you don't have power brakes.

Since I'm just throwing info out there anyhow, I believe that the Lincoln Mark VIII's from 1993-1996 had QT MC's as well...27mm x 36mm which was a 4-wheel disc car to begin with, plus is up in the bore diameter range of most full size trucks. It might bolt up easier to a Ford power booster as well compared to a GM unit.

More as just a point of interest, Mercedes has been doing this for years in their cars...since the early 70's I think, so it's not a really new idea. I think that the revised CAFE standards are just forcing the OEM's to dig a little deeper for every fraction of a mpg that they can get for the least investment.

 

[BeeFast]

Brake upgrade is on my back burner for now. I have disk/drum. I will be upgrading to a Hydro Boost system. One nice feature if you are using a Borgeson box, the power steering pump will supply pressure for both and by removing the vac booster, save that valuable vacuum for the engine. You really have to have a tight system since the clamping force is up to 2500psi. Also if you have older calipers you might want to replace them with new to avoid caliper spread.

 

[WileERobby]

Switch to drums all round. Some members swear by 'em....

Yeah, they swear after rear-ending a tractor-trailer

 

[WileERobby]

Switch to drums all round. Some members swear by 'em....

Yeah, they swear after rear-ending a tractor-trailer

 

[pnora]

Brake upgrade is on my back burner for now. I have disk/drum. I will be upgrading to a Hydro Boost system. One nice feature if you are using a Borgeson box, the power steering pump will supply pressure for both and by removing the vac booster, save that valuable vacuum for the engine. You really have to have a tight system since the clamping force is up to 2500psi. Also if you have older calipers you might want to replace them with new to avoid caliper spread.

What and the hell is caliper spread?

 

[4mulas]

Switch to drums all round. Some members swear by 'em....

Do you mean some members swear AT them?

 

[Fran Blacker]

Can you put a thicker pedal stop to take up some slack? Just make sure brakes don't drag.

 

[themechanic]

Mine work fine but after driving late model cars, I want what they are having!

The Charger affectionally known as Ginger....

View attachment 1162727

The current setup is the 1975 A body knuckles, 12" Cordoba discs with a 2.75" F-M-J body iron caliper, a 10.7" rear disc with a 1.5" single piston caliper and a 1975 Dart power booster and disc/drum master cylinder. Drum/drum distribution block. It fits, it works but it could be better. When I changed to the 5 speed earlier this year, the brake pedal had to be changed. I had modified the old pedal with the pushrod hole up higher; this resulted in a more favorable pedal ratio. Now there is a slightly greater amount of free travel before the brakes start to bite.
I don't know if a bigger set of rotors and calipers would make the difference. It isn't as if I am overheating the brakes from hard use. I don't think that I have ever had brake fade with this car with this setup. I have heard suggestions that old brake hoses can bulge out under pressure. This "lost motion" would result in the calipers "seeing" a delay in pressure or even some reduction of it.

View attachment 1162728

My brake hoses were replaced about 5 years ago so they should be fine. I'll check though.
I remember reading an article in Hot Rod or Car Craft many moons ago about a car that had what they called a "Quick take up" master cylinder. I have never heard of that since then.
In short, I'm wondering if there is some type of master cylinder, power or otherwise, that reacts faster than what I have. The pedal has more free play than before but when it starts to bite, it works. The pedal never gets near the floor. It never feels spongy either.
My system has no leaks. The car stops fine, it just used to stop better. I know that the disc/drum master cylinder sounds like a mismatch but it worked quite well before the pedal swap. I could pull the pedal and modify it like I did with the automatic pedal but I'm curious if there is something available that feels more like a modern car.
In 2012, I wanted to switch to a manual master cylinder. I had 4 to choose from, with three different bore sizes and all of them resulted in a similar fashion: Hard pedal and poor stopping force. I like the idea of a manual braking system for the weight savings and for the less cluttered look. I'd try that again if I could be reassured that I could make it work.

Wayne the Ramman, Inc, has a video explaining why not to use manual disc brakes on a street driven car. He's talking about Mopar equipped, not Baer or Wilwood.

To my knowledge, if you have disc/disc you need a disc/disc MC.

Cass told me when I bought the Doctor Diff 4 wheel disc system for the Coronet I could still use the drum distribution block.

Send Cass an email.

 

[themechanic]

BTW, I tried 2 different disc/disc MC from Summit and the plastic caps leaked. I bought Steve's (AKA biomedtech) Doctor Diff kit for the Cuda and don't need the MC that came with it. It's the plastic cap 2 hole design. So, I have 3 of these if you want one pay for shipping. But they're cheap on Summit.

 

[Kern Dog]

Smaller bore diameter master cylinder will give you more clamping force. I run a manual 15/16 aluminum master from dr. Diff and am happy with it.

On an aside, how do you check/add air into those tires? Is there more room than it looks like on the valve stem?

With the valve stem on the inside, it is not easy but not too difficult either.

 

[themechanic]

Have you tried the different brake pad materials? Like those from EBC Brakes?

https://ebcbrakesdirect.com/automotive/dodge-usa/charger/7.2-69-74/2574

 

[themechanic]

https://www.summitracing.com/search/part-type/brake-pads/year/1969/make/dodge/model/coronet

 

[Kern Dog]

It isn't a matter of the brakes not working, it is the gap between pressing the pedal and the brakes reacting. The increased leverage I had with the automatic brake pedal went away when I changed to this manual trans pedal.

 

[rikkitik]

I had a somewhat similar issue with mine as well. 10.7's in back.
A couple things I learned were,
The most commonly used rear caliper, for this setup, comes from a Cadillac Eldorado. It has a mechanically actuated parking brake. The calipers are NOT "self adjusting", there is a mechanical ratcheting action that adjust pad position with parking brake use. If the parking brake is not used, the pads will barely contact the disc, and have long pedal travel.
Another reason these calipers are in a lot of kits, is that the fluid displacement requirements are very similar to drum slave cylinders, negating a need for an M/C change.
I talked to Leed's Brakes and another company (crs though), both provided the info.

 

[Kern Dog]

Thanks. These rear calipers are from a Ford Mustang as part of the Dr Diff kit.