master cyl.

[famous bob]

I have full disc brakes on my 68 fastback, I used an 86 dodge diplomat alum. master cyl, and the original tee for the front and back (both manual )
I had an occasion to have to really get on them hard a while back because of showing off, and it took more leg to stop then I wanted .
What are you guys running for full manual discs ?????

 

[KosmicKuda]

Smaller MC bore will lessen the effort.
I use a 73 A-body power disc brake MC but run manually. I believe the bore is 15/16. I've also tried 1-1/32" and 1-1/8" bores.
The 1-1/8 bore gives a very hard pedal.
1-1/32 bore is livable.
15/16 feels best to most people.

You can measure your bore on the back where the push rod contacts the piston. (Maybe from inside the car)

 

[MRGTX]

I have full disc brakes on my 68 fastback, I used an 86 dodge diplomat alum. master cyl, and the original tee for the front and back (both manual )
I had an occasion to have to really get on them hard a while back because of showing off, and it took more leg to stop then I wanted .
What are you guys running for full manual discs ?????

I have the stock non-boosted MC for my 73 front disk/rear drum car which is now squeezing four disks (Stock front, Ford Exploder rear disk). Mine take a lot of pedal pressure as well...and I'm thinking of trying braded lines, aggressive pads before considering a new MC.

Just a thought...

 

[oldkimmer]

Good brake pads make a big difference. Kin

 

[George Jets]

A bodies manual discs/drums 15/16" on the bore works well.

Smaller bore masters give softer pedal to push and a little more throw. Dropped down a size on the B body too on the manual brakes, drums/drums
15/16" bore much much better !

 

[famous bob]

A bodies manual discs/drums 15/16" on the bore works well.

Smaller bore masters give softer pedal to push and a little more throw. Dropped down a size on the B body too on the manual brakes, drums/drums
15/16" bore much much better !

Willwood discs on the front , unknown on the back / was installed new by the guy I bought the dana 60 from when he built it .
It does have a 15/16 master cyl on it !!
NEW everything , including braided brake lines on front.

 

[George Jets]

First thing I would test famous bob is the simple brake lock test. Take your car to a no traffic gravel road, go 10 mph, then apply the brakes starting gradual then hard until they all 4 lock up and slide in the gravel.

Now go back and check the tire slide marks in the gravel. If all 4 have come on at the same time that is what you want. If the fronts come on first or if the rears come on first this is not good. You want to make sure all 4 wheel brakes are coming on at the same moment in time. This pedal hardness is the next step up the diagnostics chain after you figure out what is going on with this first test.

More to come . . .

 

[George Jets]

Famous Bob you are saying that you used the "Original Tee" that I call the Distribution Block on the frame below the master cylinder. So more than likely this is a Drum/Drum distribution block, unless your car came with like the Kelsey Hayes 4 piston front discs from the factory. If you have a factory front disc/drum brake car that you converted to Willwoods on the fronts and Other Discs on the rear. Now you have a Disc/Drum distribution block with a built in metering valve for front disc brakes in this senario.

Sake of conversation: In round numbers front disc brakes take 3,000 psi pressure to actuate where rear drums take 300 psi to actuate. Kind of looking like you need to get a Disc/Disc Distribution Block on there so that you are sending out the same line pressure to the fronts as you are sending to the rears.

Watch this RamMan youtube video on the Mopar Brake systems and see if you can pick up on what is out of place for your new aftermaket disc/disc setup.

Great Video explains the Mopar Hydraulic Brake System very very well.

 

[famous bob]

Famous Bob you are saying that you used the "Original Tee" that I call the Distribution Block on the frame below the master cylinder. So more than likely this is a Drum/Drum distribution block, unless your car came with like the Kelsey Hayes 4 piston front discs from the factory. If you have a factory front disc/drum brake car that you converted to Willwoods on the fronts and Other Discs on the rear. Now you have a Disc/Drum distribution block with a built in metering valve for front disc brakes in this senario.

Sake of conversation: In round numbers front disc brakes take 3,000 psi pressure to actuate where rear drums take 300 psi to actuate. Kind of looking like you need to get a Disc/Disc Distribution Block on there so that you are sending out the same line pressure to the fronts as you are sending to the rears.

Watch this RamMan youtube video on the Mopar Brake systems and see if you can pick up on what is out of place for your new aftermaket disc/disc setup.

Great Video explains the Mopar Hydraulic Brake System very very well.

It had manual drum brakes on it to start with, I retained the tee/distribution block and used it on the new everything disc brake system . No valves , just a tee /stock 68 form S .

 

[72bluNblu]

Willwood discs on the front , unknown on the back / was installed new by the guy I bought the dana 60 from when he built it .
It does have a 15/16 master cyl on it !!
NEW everything , including braided brake lines on front.

So the issue with this is that you don't really know what you're running for caliper piston areas. The determining factor for how stiff the pedal will be is the ratio of the master cylinder bore to the caliper piston bores. 15/16" is a good rule of thumb for these cars with manual disks, but it still comes down to what that ratio is.

If the pedal is still too stiff for you, you can go with a smaller diameter master cylinder bore. Keep in mind that will lengthen the throw of the brake pedal, so you don't want to go too crazy with it or you'll hit the floor before you run out of pedal stroke.

The other thing is that just running a drum/drum tee your front/rear distribution is fixed, and it may not be ideal for your car. An adjustable proportioning valve would let you determine the front/rear split, which can effect that pedal effort too. That said, I have an adjustable valve and I'm running it wide open on my car, so it's basically just a tee. But my rear disk conversion is new and I wouldn't say I have it fully dialed in yet. And again, that front to rear bias depends on a lot of things, caliper piston area, rotor size and swept area, weight balance, etc, etc. So what works on one car isn't guaranteed to work on another, especially if you don't know what disk conversion you have in the back.

 

[famous bob]

First thing I would test famous bob is the simple brake lock test. Take your car to a no traffic gravel road, go 10 mph, then apply the brakes starting gradual then hard until they all 4 lock up and slide in the gravel.

Now go back and check the tire slide marks in the gravel. If all 4 have come on at the same time that is what you want. If the fronts come on first or if the rears come on first this is not good. You want to make sure all 4 wheel brakes are coming on at the same moment in time. This pedal hardness is the next step up the diagnostics chain after you figure out what is going on with this first test.

More to come . . .

Not going to do gravel road in my fish, big tires in back , new paint -------------------

 

[famous bob]

So the issue with this is that you don't really know what you're running for caliper piston areas. The determining factor for how stiff the pedal will be is the ratio of the master cylinder bore to the caliper piston bores. 15/16" is a good rule of thumb for these cars with manual disks, but it still comes down to what that ratio is.

If the pedal is still too stiff for you, you can go with a smaller diameter master cylinder bore. Keep in mind that will lengthen the throw of the brake pedal, so you don't want to go too crazy with it or you'll hit the floor before you run out of pedal stroke.

The other thing is that just running a drum/drum tee your front/rear distribution is fixed, and it may not be ideal for your car. An adjustable proportioning valve would let you determine the front/rear split, which can effect that pedal effort too. That said, I have an adjustable valve and I'm running it wide open on my car, so it's basically just a tee. But my rear disk conversion is new and I wouldn't say I have it fully dialed in yet. And again, that front to rear bias depends on a lot of things, caliper piston area, rotor size and swept area, weight balance, etc, etc. So what works on one car isn't guaranteed to work on another, especially if you don't know what disk conversion you have in the back.

Dual piston willwoods in front, single piston in back (I think ), not sure what brand, suspect ford or chevy, could be mopar or aftermarket too!)
Did Chrysler ever have a 7/8" master cyl. ?? Be fine if it just applied a little more pressure , per foot pressure . The engine slows the car down when I get off the gas enough , I never had to get on them real hard before . ??????

 

[72bluNblu]

Dual piston willwoods in front, single piston in back (I think ), not sure what brand, suspect ford or chevy, could be mopar or aftermarket too!)
Did Chrysler ever have a 7/8" master cyl. ?? Be fine if it just applied a little more pressure , per foot pressure . The engine slows the car down when I get off the gas enough , I never had to get on them real hard before . ??????

Like I said, if you wanted to calculate this out and actually work out the ratio you have now compared to what your new ratio would be you'd have to know the diameter of all the caliper pistons, including the rear. That's not entirely necessary, since you already know you want the pedal to be lighter and you're not changing the calipers you can just go with a smaller bore master cylinder.

Wilwood and several others make aftermarket master cylinders in 7/8", I don't know if there's anything Mopar that would work in this situation.