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Discussion Starter · #1 ·
I did a manual disc brake Maverick master cylinder conversion: I have a 4 speed 69 Cougar originally with manual drum brakes. I replaced everything up front from a power disc brake donor car. I used a new MC for PDB without the booster. It all worked well but the pedal was a little high and pretty stiff. Then I heard about the Maverick trick for a softer pedal feel because of the smaller bore. I did that along with rebuilding the DB proportioning valve and an adjustable brake push rod to get the pedal lower. All is good except the braking sucks and I can not lock them up in a panic type hit. The car does not pull left or right. The calipers and wheel cylinders were rebuilt. All 3 rubber lines converted to SS. It took 4 new not rebuilt MC's from Summit and NAPA before I could get one to bench bleed. The pedal does seem to still be a little spongey even after the countless amount of bleeding with quarts of Valvoline Synthetic DOT3/4 brake fluid. The tires are larger than stock 245-60-14 BFG all around. The car does not seem to dive forward in hard braking. I don't want to convert to power brakes. Do you think I should put on an adjustable proportioning valve? Replace the disc pads with stickier type than the Auto Zone standard? Anyone's thought on this would be appreciated. Thanks in advance.
 

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Also, are there a multi piston caliper available as a direct bolt on? I can't locate a brand that doesn't include a complete kit and hardware.
You have a nonstandard configuration, so you need to do a bit of tweaking to make it work correctly. You should be able to lock up the brakes. The fact you can’t shows you are not creating enough pressure. There are a couple potential reasons.

1. What brake pedal are you using, Power brake or Manual brake? The Power brake pedal is longer and reduces pedal effort but requires the pedal to travel further if there is no booster. A Manual pedal will make it hard to generate the pressure for stopping without a lot of force.
2. Master Cylinder. It may be too small or it may not have a residual valve. If it doesn’t have the valve you need a different MC or you can add an inline Residual valve.
3. Drop the crappy brake pads and invest in quality pads. Porterhouse are an excellent choice.
4. Once you can properly lock up the brakes, assess if the rear is locking up before the front. If they are you’ll need an adjustable Proportioning valve To dial in the front to rear bias.
 

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Discussion Starter · #4 ·
You have a nonstandard configuration, so you need to do a bit of tweaking to make it work correctly. You should be able to lock up the brakes. The fact you can’t shows you are not creating enough pressure. There are a couple potential reasons.

1. What brake pedal are you using, Power brake or Manual brake? The Power brake pedal is longer and reduces pedal effort but requires the pedal to travel further if there is no booster. A Manual pedal will make it hard to generate the pressure for stopping without a lot of force.
2. Master Cylinder. It may be too small or it may not have a residual valve. If it doesn’t have the valve you need a different MC or you can add an inline Residual valve.
3. Drop the crappy brake pads and invest in quality pads. Porterhouse are an excellent choice.
4. Once you can properly lock up the brakes, assess if the rear is locking up before the front. If they are you’ll need an adjustable Proportioning valve To dial in the front to rear bias.
Thankyou "Flade" for the response
1. I am using the original manual pedal
2. I will look into the MC to see if it has a built in residual valve There is not an external one on the car as I remember but I look again.
3. Did you mean Porterfield brake pads?
4. I used at first a new power brake MC with 1" bore. The pedal height was higher and more firm with a little more effort to brake than with manual drum brakes setup. I could get some minimal lock up, but never really paid that much attention to how much. I ran it this way for about 4 years. I read about going to a 7/8" or 15/16" bore for a little softer pedal. I changed the MC to a 1970s Maverick manual disc brake 15/16" bore and used an adjustable push rod to dial in the pedal height I wanted. The pedal is softer but not good braking! Maybe the Mavericks used an external residual valve, I'll have to look into that. The proportioning valve had a weeping leak so I rebuilt it when I did all of the MC changes. All four brakes seem to bleed the same and I use a centering pin in the junction block when bleeding.
I may have to go back to the PB MC and use the adjustable rod to get the height right and live with the extra firm pedal. That does entail redoing the lines again as they are different fitting sizes at the MC. Maybe the residual valve is the answer so I will look into that first. That is on the rear brakes correct? I'll also go out and drive the car and see if I give it a quick double pump then hard to maybe simulate a residual valve but I doubt that will do anything. Also I do have the drums adjusted up fairly tight and all four brakes do back off correctly when up on the jack stands.
Thanks in advance.
 

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Thankyou "Flade" for the response
1. I am using the original manual pedal
2. I will look into the MC to see if it has a built in residual valve There is not an external one on the car as I remember but I look again.
3. Did you mean Porterfield brake pads?
4. I used at first a new power brake MC with 1" bore. The pedal height was higher and more firm with a little more effort to brake than with manual drum brakes setup. I could get some minimal lock up, but never really paid that much attention to how much. I ran it this way for about 4 years. I read about going to a 7/8" or 15/16" bore for a little softer pedal. I changed the MC to a 1970s Maverick manual disc brake 15/16" bore and used an adjustable push rod to dial in the pedal height I wanted. The pedal is softer but not good braking! Maybe the Mavericks used an external residual valve, I'll have to look into that. The proportioning valve had a weeping leak so I rebuilt it when I did all of the MC changes. All four brakes seem to bleed the same and I use a centering pin in the junction block when bleeding.
I may have to go back to the PB MC and use the adjustable rod to get the height right and live with the extra firm pedal. That does entail redoing the lines again as they are different fitting sizes at the MC. Maybe the residual valve is the answer so I will look into that first. That is on the rear brakes correct? I'll also go out and drive the car and see if I give it a quick double pump then hard to maybe simulate a residual valve but I doubt that will do anything. Also I do have the drums adjusted up fairly tight and all four brakes do back off correctly when up on the jack stands.
Thanks in advance.
Yes Porterfield…Autocorrect issue….

A 67 Mustang MC or later will have a residual valve in the port for the rear brakes. It’s purpose is to prevent the drum brakes from fully retracting w hich would cause excessive pedal travel. Some aftermarket MC do not include the residual valves (including MC designed for 4 wheel disks). In these cases you can add an inline residual valve.

I also have to wonder if the real problem is the Manual Pedal. It was designed for drum brakes and may not provide enough leverage for the disk brakes to feel right.
 
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