[Dusterva]

Did a front drum to disc conversion on a 66 Coronet convertible. Manual not power brakes. Bought kit from Right Stuff. Ran newlines and installed the kit. When bleeding the brakes, and all air removed, the front brakes are locked with no pressure on the pedal. Adjusted the new actuator rod from loose to firm, no difference. Bought new hoses, no difference. Bought new master cylinder, calipers no change. These replaced the new parts from the kit. The only way to unlock is to bleed pressure form the system. Front and rear systems are independent. The proportioning valve is for rear brakes only(still drums in rear). Right stuff is stumped as are all my car friends. The Right stuff kit uses parts from a 73-74 mopar A body according to Right Stuff. Does the system require a Mopar Combination Valve or other device?

 

[Dusterva]

Did a front drum to disc conversion on a 66 Coronet convertible. Manual not power brakes. Bought kit from Right Stuff. Ran newlines and installed the kit. When bleeding the brakes, and all air removed, the front brakes are locked with no pressure on the pedal. Adjusted the new actuator rod from loose to firm, no difference. Bought new hoses, no difference. Bought new master cylinder, calipers no change. These replaced the new parts from the kit. The only way to unlock is to bleed pressure form the system. Front and rear systems are independent. The proportioning valve is for rear brakes only(still drums in rear). Right stuff is stumped as are all my car friends. The Right stuff kit uses parts from a 73-74 mopar A body according to Right Stuff. Does the system require a Mopar Combination Valve or other device?

 

[ImperialCrown]

A disc/drum combination valve should be used for safe brakes. The metering portion of the valve will delay front disc application until the rear shoes will move toward the drum and begin to apply.
The residual valves hold a few psi on the drum wheel cylinders to keep the cup seals flared to help sealing. The residual pressure is low enough where it can't overcome the shoe return spring tension, so the drum brake is not applied or dragging.
Residual valves may be at the m/cyl ports, not the combination valve.
The disc brake circuit does not use a residual valve and if one is present, it will apply the calipers and cause the front brakes to drag.
Right stuff needs to understand the basics of disc/drum differences and safe conversions. AAJ brake conversions may be more expensive, but they are the complete conversion kit.

 

[valiant67]

The residual valves hold a few psi on the drum wheel cylinders to keep the cup seals flared to help sealing. The residual pressure is low enough where it can't overcome the shoe return spring tension, so the drum brake is not applied or dragging.
Residual valves may be at the m/cyl ports, not the combination valve.
The disc brake circuit does not use a residual valve and if one is present, it will apply the calipers and cause the front brakes to drag.

^^^This

 

[Dusterva]

Took one Master cyl apart and there is nothing behind the brass seat so I assume there is no residual valve. The kit came with a proportioning valve but it is for the rears only. After changing the Master Cyl to a new unit still does the same. Right Stuff is no help at all.

 

[chuzz]

I'd see if they'd send a refund since they can't figure out how to make their own parts work properly. Return the stuff, get your money back and use the company suggested by Imperial Crown. That's crazy.

 

[valiant67]

Took one Master cyl apart and there is nothing behind the brass seat so I assume there is no residual valve. The kit came with a proportioning valve but it is for the rears only. After changing the Master Cyl to a new unit still does the same. Right Stuff is no help at all.

Are you sure there's no residual valve at the port on the master cylinder where you are connecting the front brake lines?
That's where it is on a Mopar master cylinder as I understand it.

 

[Bearhawke]

Next time the front brakes lock up, try unbolting the master cylinder from the firewall; if still locking, something's amiss with either your new M/C and/or (possibly) the proportioning valve. If front brakes DO release with the M/C loosened, then there's an issue with the pedal push rod being either too long or, possibly an issue with brake pedal mtg geometry under the dash.

 

[68RT]

You should be able to see the cup go back behind the small hole. That is how the pressure is released on a master cylinder.

 

[ImperialCrown]

 

[68RT]

You should be able to see the cup go back behind the small hole. That is how the pressure is released on a master cylinder.

I mean the small hole visible looking down into the reservoir.

 

[AC TC]

The actuator rod should not be firm because it pushes the master cylinder invards and that Closes the compensator hole in the master and locks your brakes. ( compensator hole is from the reservoir down into the master cylinder bore, the sealing should open/ pass this when the brakepedal is up.Theres one hole for each Circuit.)
- Loosen the rod instead.

 

[AC TC]

Wich spindles did you use?
- some kits are sold with later b-body spindles wich aren the same geometry as the earlier ones and they will mess up front end geometry.

 

[Bearhawke]

Wich spindles did you use?
- some kits are sold with later b-body spindles wich aren the same geometry as the earlier ones and they will mess up front end geometry.

That won't make any difference if discussing the front brakes locking up too soon. Too, the only design major difference between the traditional1973-76 A/E body spindles vs the F-M-J-R-W vehicles is the newer ones are about 1/2" taller.

 

[AC TC]

It was more a general question.
- as for the ts its about only two things that can make this happen.
Compensator port doesent open, adjust mc pushrod.
There is some kind of restrictions in the break tubing/ hooses, if it was only one side id suspect a bad hoose.