Posted By: WyleECoyote
68 Road Runner - Thinking ahead... - 05/23/14 06:26 PM
My Road Runner has manual drum brakes, all 4-corners. After being in storage for 21 years, the master cylinder is empty and rusted so I plan on a new mc, wheel cylinders, lines, etc.
Just to get the car mobile again, I'm using the local parts stores and getting what can be had from them.
Eventually I want to add disc brakes to the front. In an effort to plan ahead;
1. When I switch to disc brakes, will I have to change the master cylinder?
2. If I do have to change the master cylinder, can I install the one that is needed for disc brakes now and will it work with the drums?
3. Are manual disc brakes much more effective over drum if they aren't power disc brakes?
I used the forums search and couldn't find my answer.
Thanks for inputs!
Posted By: therocks
Re: 68 Road Runner - Thinking ahead... - 05/23/14 09:19 PM
I use the iron masters.I get 70 C body either drum/drum or disc/drum.They bolt right up.My 65 I had A body spindles.I changed to the taller late B body ones.Car handles great and has manual discs.Stop great even at 120 at the track.The drum master should have a residual valve in both ports.Disc only has one for rears.A body discs along with Volarie,Aspen IIRC magnum etc will also fit.They have the taller spindles which are about 1/2 inch or so.My 65 got the alingnment in better with tall knuckles.Rocky
Posted By: therocks
Re: 68 Road Runner - Thinking ahead... - 05/24/14 02:16 PM
Correct.the master bolts right up.IIRC you can get a drum drum master and when you add discs there is a tiny piece in the port for the line that can be pulled out so no pressure stays on the discs.We have 70 c masters on my 65 manual and my kids 62 300 power drum.If you have power you will have to check and maybe adjust the rod for the master.My kids 62 was a single so we needed to thread the rod out a bit.I got both at Advanced remans.No problems after at least 15 years.Rocky
Posted By: Pynzo
Re: 68 Road Runner - Thinking ahead... - 05/24/14 03:39 PM
You can pull the residual valves out when you change over to discs. They are behind the tube seats in M/C. Raybestos M/C rebuild kit # MK474 comes with new tube seats and valves.
Posted By: RapidRobert
Re: 68 Road Runner - Thinking ahead... - 05/24/14 04:37 PM
As you know drums use RPV and discs do not. Earlier drum setups used an RPV in the MC and later on they switched to using a metal quarter sized disc behind the wheel cyls' neoprene cup seal to do the same thing (better seal/no air in/quick take up on the pedal). Stick a drill bit into the brass cone seat & you'll feel the RPV if it has one (very few MC's do now) as it is just a piece of neoprene and a spring for a crude 1 way valve to maintain a minimal psi. The drum half can get by with or without an RPV but discs cannot have one other than an aftermarket 2 psi one but that's not applicable here. Get a disc/drum MC now that has the larger front disc half & you're set for when you later switch to discs in the front. I believe Eberg (eBay) has rear wheel cyls with the metal discs but the main adv of them is he has em in the smaller bore size.
Posted By: Pynzo
Re: 68 Road Runner - Thinking ahead... - 05/24/14 05:02 PM
Glad to know that. I rebuilt my drum brake M/C and did not put in the new seats/ residual valves. The remanufactured M/C I had didn't have them so I figured why bother. Thanks!
Interesting. 
