Inexpensive “Cordoba” Brake Upgrade for 70 Road Runner

[autoxcuda]

I remember reading back in the late 80’s the R body setup was the one to pull from the junkyard. The only problem was not many were made. I never saw one in the yards.

Mind you, this was before the aftermarket kits that have all the parts for the conversion.

I think the R body had the 11.75 with slider adapters. Or maybe the police versions. Not many police versions, but I remember seeing them in the junkyards back in the day.

Old picture I found on web:

 

[bitterbelvedere]

My apologies to Op for sidetracking thread. When i initially put this brake setup on my Valiant I was sold a power brake master with a .96 (?) Dia bore for a power disk braked late "A" body. But when used on my manual brake setup it took noticable extra effort to apply the brakes. After replacing it with the correct 1.06 dia bore master pedal effort was noticeably better (more sensitive and less effort to apply). To this day I'm still surprised at the difference in brake feel at pedal for such a small difference in bore dia. Given that, moving up to a 1.1 dia bore would make me think (not know) you would have even less pedal effort to push more fluid to brakes leading to concerns that the increased fluid flow could lead to more frequent/easier rear wheel lockup in panic situations. Hope Op updates thread after system together with his feelings/experiences.

 

[Sixpactogo]

Soft pedal, bled 3 times & shop says the master cylinder doesn’t have enough force. It won’t lock up the brakes

You don't by chance have a single diaphragm booster in there do you? In your first post, you said you have a OEM power disc set up. That would mean you should already have the dual diaphragm booster that is needed to satisfy front discs that need twice as much force as drums do. If you don't have enough boost it won't matter how many feet you put on that pedal.

 

[PurpleBeeper]

You don't by chance have a single diaphragm booster in there do you? In your first post, you said you have a OEM power disc set up. That would mean you should already have the dual diaphragm booster that is needed to satisfy front discs that need twice as much force as drums do. If you don't have enough boost it won't matter how many feet you put on that pedal.

Factory power brake booster

 

[Sixpactogo]

Factory power brake booster

Factory drum or Factory disc? Factory drum brakes used a single diaphragm booster. Disc brakes require twice as much boost so they got the dual diaphragm booster. If your car had factory drum brakes and you or someone converted to front discs without upgrading the booster, that would be good reason for not having enough force to lock the brakes. It is not the master cylinder's fault.

 

[bc3j]

Soft pedal, bled 3 times & shop says the master cylinder doesn’t have enough force. It won’t lock up the brakes

What’s the MC bore size? I use the Cordoba rotors, the 2.75” slider calipers, manual brakes, Dr Diff’s aluminum 1.031 MC. Stops great. I used a Motive pressure bleeder to bleed. If you have a metering valve you’ll need to have the pin pulled open to pressure bleed the fronts. I found the Motive bleeder to be extremely efficient bleeding the brakes. I originally used a 15/16” MC and had uncomfortably long pedal travel and inability to lock the brakes. The 1.031 MC solved that problem without excessive pedal pressure.

 

[DeltaV]

I think the R body had the 11.75 with slider adapters. Or maybe the police versions. Not many police versions, but I remember seeing them in the junkyards back in the day.

Old picture I found on web:

View attachment 1672063

Yes, the St. Regis came with the slider type and 11.75" disc, as well as other models:

E: St. Regis (already mentioned)
T: Newport/New Yorker
S: Cordoba
X: Magnum

DISC
Type-All Cast Iron; Ventilated
Diameter-Outside: 11.75"
Diameter--Inside: 7.555"

Source:
1979 Chrysler Plymouth Dodge Chassis-Body Service Manual
________________________________________
Comments:
1: Cordobas may still be available in some salvage yards.
2: 1979 Chrysler 300 cars are in some Mopar salvage yards. For example, AMS Obsolete in Fairmont, Georgia has eight of them listed as parts cars.
3: The caliper pistons in my 1979 Chrysler 300 are phenolic, not steel. I had one go south after around 12 years of driving since new. Degradation from heat may be more of a factor than constant exposure to brake fluid. Replacement phenolic pistons can be found. I haven't looked lately as I don't need any right now.

_________________
@PurpleBeeper

 

[autoxcuda]

Yes, the St. Regis came with the slider type and 11.75" disc, as well as other models:

E: St. Regis (already mentioned)
T: Newport/New Yorker
S: Cordoba
X: Magnum

DISC
Type-All Cast Iron; Ventilated
Diameter-Outside: 11.75"
Diameter--Inside: 7.555"

Source:
1979 Chrysler Plymouth Dodge Chassis-Body Service Manual
________________________________________
Comments:
1: Cordobas may still be available in some salvage yards.
2: 1979 Chrysler 300 cars are in some Mopar salvage yards. For example, AMS Obsolete in Fairmont, Georgia has eight of them listed as parts cars.
3: The caliper pistons in my 1979 Chrysler 300 are phenolic, not steel. I had one go south after around 12 years of driving since new. Degradation from heat may be more of a factor than constant exposure to brake fluid. Replacement phenolic pistons can be found. I haven't looked lately as I don't need any right now.

_________________
@PurpleBeeper

I would not be surprised if the price of Caliper Adapters at a Mopar salvage yard would be more than buying them new through Dr Diff.

 

[PurpleBeeper]

Factory drum or Factory disc? Factory drum brakes used a single diaphragm booster. Disc brakes require twice as much boost so they got the dual diaphragm booster. If your car had factory drum brakes and you or someone converted to front discs without upgrading the booster, that would be good reason for not having enough force to lock the brakes. It is not the master cylinder's fault.

Original power front disc brakes, rear drums