Rear Disc brakes

I have a 71 Mach1 with factory front disc and rear drum brakes. I am changing the rear drum to disc. Do I need to get a different booster, master cylinder and poportioning valve or can I use the one I have?

Booster will be fine as is. I replaced the MC and removed the proportioning valve, adding an adjustable proportioning valve to the rear circuit. MC Bore size will affect brake feel. If you have a stock or mild cam it will work nicely.

Very few rear disc brake kits work with 15" factory wheels.

Parking brake hook up can be challenging- I moved my brake to the transmission tunnel and routed lokar cables.

All in all, I think if I was building another similar car, I would leave the drum brakes in back. So much of the braking is up front anyways, that upgrades on that end make more sense and cost less after factoring in all the changes.

I converted my rear drum to disc using the SSBC standard duty kit. It uses single 45mm pistons. Because this system requires a low volume of fluid to be moved, I was able to use the stock master cylinder while maintaining good braking power and a firm pedal. If you are using a multi piston system, you might want something with a larger piston (less pressure but more volume moved).

Just to add, I also tried a 1 1/8 piston MC and found the stock size provided better pressure. As far as parking brake. The kit I used has a good parking brake system. I ordered the shorter parking brake cable 2 1/2 inches longer from Inline Tube to fit the new system. I upgraded the three parking brake cables to stainless steel since I was ordering new units. I also found my set up worked better with a smaller power booster, which was also a brand new unit. The rebuilt stock replacement gave me a spongy pedal that would suddenly apply pressure to the braking system. It did this with the 1 1/8 piston MC and the stock unit. Might have been rebuilt wrong but I already had the GPS booster so I stuck with that.

I am very happy with the brake system now. This is my set up:

Stock MC

GPS 9 inch power booster (brand new)

SSBC rear disc brake kit

stock front disc

SSBC proportioning valve/distribution block

Inline Tube stainless cables

3 pc stainless braided hoses from NPD

SSBC slotted rotors front and back