68 dart Disc brake up grade, what MC?

[Dakota_Don]

Hi, I am doing a disc brake swap.. I have a 68 dart with manual drum brakes, can I swap the MC out for a 72 dart with power disc brakes onto my 68 dart and leave my 68 manual ?

if I use a MC from a 72 dart w/Manual disc, the MC piston dia is 1 1/32 bore.
would it be better to go to a 1 1/8th bore dia MC off a 87 dodge van? I dont want my pedal so hard it takes both feet to stop like it does now.

also will I need p Valve for the disc? or will the 68 Drum P-valve work?

here is the kit i am thinking about using..

www.scarebird.com
Mopar “A” body 1965-72 10”, 1960-72 9”
Front Disc brake conversion instructions
Crack front wheel nuts loose, chock up rear wheels. Jack up front end of car, support outer control arms with jackstands. Remove front wheels, drum/hub assembly. Put a few drops of penetrant oil on brakeline nuts where they screw into rubber lines.
Take drum/hub assembly and remove studs. Best way to do this is to center punch the head from the inside. Then pilot drill about ½” deep, then drill off head with 5/8” diameter bit. Clean off wheel surface and register with wire wheel or beadblaster. Replace studs with ¼” longer or more studs, such as NAPA #641-1563 (10”) or #641-1560 (9”)
Disconnect brake flexible line at frame by unscrewing hardline nut with flare wrench, then removing clip. Undo and remove drum retaining bolts. Remove drum backing plate, hose and all drum hardware in one assembly. Clean off spindle assembly well.
Place adapter plate over spindle with caliper bolt retaining nut welds facing inward for the Ten’s, outward for the Nines, and caliper opening to the rear for Ten’s, Nine’s goes forward of the axle. Make sure no dirt is lodged between spindle and plate.
Drill out wheel stud holes with pattern supplied. Cut out pattern with scissors, then spray with light oil or WD-40 and lay on rotor. Lightly punch for holes, then remove and punch harder. Drill out holes ½” diameter. Verify that rotor lays flat against hub by fitting rotor backwards onto hub. If the stud knurls interfere with rotor, countersink stud holes in rotor to clear knurls.
Clean and repack wheel bearings. Install new seal. Assemble hub onto spindle, tighten outer nut to spec, then secure with keeper, new cotter pin and dustcap.
Install center ring on hub. Place rotor onto hub, and run two or three lugnuts down finger tight to retain rotor. Wipe down rotor with alcohol, lacquer thinner or other cleaner.
Wash hands! Rotor must be squeaky clean.
Lubricate caliper contact point of brackets. Slide assembly into caliper bracket. Make sure bleed screw faces upward- if not, reverse sides. We recommend buying loaded calipers. Tighten caliper bolts to 35 foot-pounds. Check fitment and rotate rotor to check clearance. We used 1979 Seville front hydraulic hoses that are 15” long for the 10” drum units, 1979 Cadillac Eldorado front hoses that are 17” for the Nines. Install hose with new copper crush washers.
Master cylinder and proportioning valve specs are quite varied. I would recommend 1967-72 Dart or similar disc master cylinder for best performance match available in both power and manual flavors. Plumb in an adjustable proportioning valve in the line going to the rear cylinders, or use a disc proportioning valve
Bench bleed disc master cylinder. Mount MC on car, then gravity bleed entire system first to eliminate most of the air, then pump bleed and test, otherwise your distribution block may jam from a pressure imbalance.
Replace wheels, install lug nuts, lower car and torque nuts to spec. Test drive carefully- no hard stops, a series of smooth stops will help bed in the pads properly.

Part Application NAPA Wagner Raybestos
Rotor 1990 Chevy Celebrity 85768 BD60678 5072 or 105072
Caliper, LH 1990 Chevy Celebrity 242-2066 L107084 RC4234
Caliper, RH 1990 Chevy Celebrity 242-2067 L107085 RC4233
Brake Hose (15”) 1979 Seville front 36845 F98912 BH36845
Brake Hose (17”) 1979-82 Eldorado front 36959/36960 F98914/98914 BH36959/3696
Brake pads 1990 Chevy Celebrity AE7136M MX215

*Verify fit and length before buying Scarebird Classic Brakes LLC 20 April 2007 Version C

 

[Dakota_Don]

anyone

 

[robertob]

I used 1 1/32 non-power iron and 1 1/8 aluminum from a B-van on my old Dart and both worked fine. This was with the A-body 2.6-inch piston front calipers and small rotors with stainless braided lines. HOWEVER, you are using a different caliper piston diameter and different effective disc diameter since you're using the GM stuff. So I have no idea what your pedal ratio is going to be.

So not too many people are going to be able to answer your question properly. In general you should use the largest MC piston that you can still push with enough force to stop the car - that gives you the shortest brake pedal travel and hardest brake pedal.

Which one is it for you? Who knows. Hopefully you'll find someone that's done the scarebird conversion. (Not me - the backyard re-drilling of the rotors scares me, honestly)

 

[grumpuscreature]

I used a '74 Charger master cylinder with '75 Duster discs on my '66 Valiant. The brake pedal is not hard at all and I have brakes from the time I put my foot on the pedal until lock up at 1/4 pedal travel. No standing on a rock here.

 

[Dakota_Don]

thanks, the redrilling isnt thst big of a deal..

 

[68 Sedan]

That's the setup I'm considering using. But why does it list two different length hoses?

 

[Dakota_Don]

the reason is, the legnth. If you have 10" drums use the 15" hose, 9 Inch use the 17" hose

 

[cudajim]

Yes, you do have to change the proportioning valve. The one for drum brakes will not work with your disc brakes.