Howdy - I'm hip deep in a brake system upgrade, meaning replacing the single pot with a dual master, and replacing all brake lines and hoses. Not messing with the drums or other parts, everything else seems pretty good as stock (unless someone has DEFINITELY DO THIS recommendations). My question is the master. I got a Raybestos MC36221 from RockAuto.

The old master had a gasket at the firewall, the new one didn't come with one - is this a necessity? Should I just get some gasket material and make one?

Boot - the old rubber boot (covering the plunger through the firewall) had a flange that bolted to the back of the MC, which meant it was a tight connection to the MC. The new boot is smaller, and looks as if it just rests against the back of the MC (not sealing anything). Is that kosher? Is this supposed to provide a seal to keep fluid in, or is the piston seal inside the MC enough?

Brake line plug - I'm using the existing metering block, but plugging one of the holes. Is a simple 3/8"-24 bolt enough, or do I need a gasket or o-ring to seal it properly?

Thanks for your help - Jason

You can make that fire wall gasket that is missing; pick up a pack of assorted gasket material, its handy stuff to have around. I suspect that gasket was used to prevent under hood smells from entering passenger compartment. The rubber boot the brake pedal pushrod passes through I think is just a dust cover to help keep piston bore clean.





Are you trying to seal off the port that normally houses the low brake system pressure warning light switch, or the unused hole? (Its been a while since messing with Dart brakes I recall a plug in one of the ports). A machine bolt thread wont seal. You need a fitting that fits the flair or has some type of sealing gasket or "O" ring made to cap off high pressure situations or that switch.

A photo of what you are trying to cap off would be helpful.


And probably someone here may have the part you need in their pile of stuff.

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

If he's converting from single-pot to dual-pot master cylinder, I assume he's unplugging the rear brake line from the distribution block and plugging that hole, then running the rear line up to the master. At least that's how I did it.

For the unused hole, you need an inverted flare plug that's the same size as the fitting that came out (probably 3/16" line size). I'm pretty sure the auto parts stores have these. Check the section with the 2-3 spinning racks with all the hardware in little plastic containers. You can also get an inverted flare union fitting, to connect the existing rear line you took from the distribution block to the new line you bend up to the master.

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Somehow I ended up owning three 1964 slant six A-bodies. I race one of them.
Escape Velocity Racing

SpaceFrank, you are indeed correct, and thanks - looks like I'll spend another few hours loitering in Napa.

Thanks - Jason