[dana44]

Welcome to the forum. You may be able to find something online, otherwise, the spindle itself has to be measured for the two bearing sizes and the length/depth of the two bearings on the spindle and then get ahold of one of the conversion companies and see if they can match something up. I am not sure as to the spindle sizes for a '57, you may be able to determine whether it is swappable with something else by using the bearing numbers and seeing what else they fit. May turn out to be the same all the way up into the early '60s, which then makes it easier to do a disc conversion. Next option is to do a balljoint interchange, see if at that point other spindles could be used to then do a disc conversion.

 

[ImperialCrown]

This may basically be a 1953 Plymouth P25 chassis?
http://www.allpar.com/world/royal.html

If you haven't already, you will want to plumb this as a dual-circuit hydraulic brake system with a proportioning valve. Try:
http://www.rustyhope.com/mopardiscbrakes.html (mounting hardware only)
http://www.aajbrakes.com/rproductinfo.html (system conversion-safest way to go)

 

[mopar56]

Hi if it is the same as my 56 Dodge 1/2 ton, the drum was riveted to the hub, I simply ground and removed the rivets and I had a hub, the bolt pattern was 5 on 4.5 I beleive I then used Mazda mpv rotors but had a machine shop turn down part of the mating surface on either the hub or rotor,(cant remember) because of a clearance issue, for some reason the Dodge rotors wouldnt work, I made caliper brackets and beleive I used Jeep calipers, after all that I sold the set up and used a Volare clip, but everything did work for a reasonably cheap cost

 

[dak4x4]

Do you not also need a dual master cylinder and proportioning valve for a conversion to disc brakes?

 

[dana44]

Yes, it would be best. The front brakes take more fluid volume to work compared to the rears, so if there isn't the proper items you will (from experience) lock up the rear brakes rather easily, backwards to what cars stop as normally. I know this because the wheel cylinders on my 39 Nash are larger than the rear wheel cylinders and if not gently braking, my rear tires lock up easily, a slight design fault, and I do have a dual master cylinder and drums all around, disc would be even worse at this point.

 

[ImperialCrown]

Plus there is residual brake line pressure in drum brake systems to keep the wheel cylinder rubber cups flared out against inside the of wheel cylinders. It isn't enough pressure to overcome the shoe return springs, so the shoes aren't applied and don't drag. It is however enough pressure to keep the disc calipers partially applied to drag, heat up and wear.
You want to do a full proper conversion as safe brakes are paramount. The AAJ brake kit as shown in the post #3 link is expensive, but complete except for the metal lines which you can cut, form and flange yourself with a 25' roll of brake line and flaring tool.

 

[68RT]

Plus there is residual brake line pressure in drum brake systems to keep the wheel cylinder rubber cups flared out against inside the of wheel cylinders. It isn't enough pressure to overcome the shoe return springs, so the shoes aren't applied and don't drag. It is however enough pressure to keep the disc calipers partially applied to drag, heat up and wear.
You want to do a full proper conversion as safe brakes are paramount. The AAJ brake kit as shown in the post #3 link is expensive, but complete except for the metal lines which you can cut, form and flange yourself with a 25' roll of brake line and flaring tool.

Clarification on this: The check valve is required only on drum brakes to keep enough pressure on the wheel cylinder cups from collapsing and leaking fluid. You cannot have a check valve on a disc brake wheel cylinder or it does not retract enough and the shoes will drag causing real issues. So systems that have both discs and drums have a master cylinder that has only one check valve for the drums only and the other half has no check valve.