I recently acquired a 70 Challenger Convertible R/T. Has drum brakes on all four corners. Can I swap out the front drums to an OEM disc set up without replacing the master cylinder or proportioning valve. I would prefer keeping the under hood components as they are.

Master cylinder has to go.

Drum brakes use a different master cylinder and proportioning valve.

The drum brakes adjusters expand the shoes as the shoes wear so the fluid doesn't drop. Both sides of the master cylinder reservoir are the same size. With disk brakes the piston moves out of the caliper as the pads wear so the fluid drops and requires a bigger reservoir. That is why disk brake master cylinders have 2 different size reservoirs.

Additionally the drum brake ports often have a residual pressure valve to keep pressure on the wheel cylinder cups so they don't leak. Disk brakes do not need those.

70-72 B/E used the Kelsey Hayes set up. So 10.98" rotor small bearing. You will have a booster, disc MC, Distribution T, Meter valve from Front disc and proportioning valve for rear drums.

There is nothing wrong with drum brakes if maintained properly.

Five of my 1970 models have them and they all stop just fine.

To each their own!
I had a 70 Road Runner with properly maintained 11 x 3 drum brakes front, and 11 x 2 (I believe) on the rear. I had a much different opinion after the 1st stop from 100 mph +. It did pretty good until you got down to about 40 mph, but after that, not so good.
The next week the car had disc brakes on the front with the 11" still on the rear. A much better experience. Been putting disc brakes on everything since. Gene

Yea Right: Until you go thru a deep puddle of water then have to suddenly brake.

Agreed!.........Everything I own gets power 4 wheel disc brakes, 4 wheel drums are for Granny cars/drivers..... or those with a death wish with today's drivers/roads

do you use factory parts for 4 wheel disc conversions, or aftermarket parts/kits ?

Back in the day we learned very quickly that when going through deep puddles we draged the brakes a little.

Where are you guys driving your cars so I know to avoid those areas?

As long as you don't load up your time machine and go back to the 1970-1990s, you would be OK with the 100 mph +, at least from me.

As a note, the legal speed limit on the interstate in WY is 80 mph. At 80, they pass you like your going backwards. If high speeds, or driving through big water puddles scare you, don't come near IL or nearly any interstate highway in the southern USA, you better sat up there in Alaska. Gene

Depends on the application, intended usage, sometimes a mix of factory stuff and aftermarket, or all aftermarket, sometimes along with my own machined parts.....


MikeG

have you ever used the jeep [i forget the model] rear disc setup as described in Mopar Action magazine a while back ?
if so, how did you like it ? was it a big improvement over 11" drums ? any installation problems ?
TIA sir !

As far as rear kits, I use either SSBC or Wilwood, I really prefer the SSBC set up using modified Ford pieces, SSBC went out of business during the scamdemic but I understand they were being bought out, soon to return?....I've copied all the SSBC parts for 8 3/4/Dana 60 swaps, I just purchase the Ford calipers and rotors to complete the set up.....

I feel any 4 wheel disc set up properly designed is far superior to any drum/drum or disc/drum set up, it's a night and day comparison esp when power assisted IMHO

MikeG

you wouldn't be willing to share the SSBC blueprints with me would you ?
i'm not going into any business, but i would like to go disc on the rear of my charger.
being a retired machinist, i can make what i need, but i have never seen, nor had in my hand, a rear disc kit [of any kind] to copy the bracketry or parts list.
if you do not want to do this for whatever reason, i understand. no big deal, but i figured i would ask anyway.