Master Cylinder Valve Question

[57chevyman]

Hey Guys,
I recently upgraded my 1957 truck to a dual master cylinder with no booster... I got the "corvette style" MC from CPP....

I have drum brakes all around.

I had my mechanic who specializes in hot rods and muscle cars install the new master cylinder. He did a real nice job and ran all new brake lines and the brakes work like they should.

Here is my situation that I want some advice on:

I was advised by CPP to not use the proportioning valve that came with my master cylinder and use residual valves instead for a drum/drum application.

My mechanic hooked it up with the proportioning valve and says that its fine... but apparently its not fine because the thing is leaking. it seems to be leaking from one of the plugs that's screwed into the drivers side of the master cylinder. ( the brake lines are attached on the passenger side of the MC). I looked close and saw that the plug that is leaking was screwed in using some white plumbers tape. im bringing the truck back to the mechanic tomorrow morning.

Is the MC leaking because its defective? is it leaking because he hooked it up with the proportioning valve?

Is it OK to use the proportioning valve with all drum brakes ?

[OrrieG]

You don't use plumbers tape on brake or fuel lines. Use the proportioning valve. If your mc is frame mounted and wheel cylinders are above or near level to the mc use the residual vslves too.

[57chevyman]

Originally Posted by OrrieG

You don't use plumbers tape on brake or fuel lines. Use the proportioning valve. If your mc is frame mounted and wheel cylinders are above or near level to the mc use the residual vslves too.

it is frame mounted, so yeah its approximately level with the wheel cylinders. So , residual pressure valves should be added inline? a friend of mine said yeah, you should use residual valves to prolong the life of the wheel cylinders

im trying to understand why the MC is leaking ( slightly ). I asked the mechanic about the plumbers tape and he said " yeah we had an issue with that, but we thought it was sealed tight". its only that one spot that has the plumbers tape, so obviously they were trying to stop a leak.

is the lack of residual valves causing too much pressure in the MC, and causing the leak? The residual valve is like a check valve right? so it keep a few pounds of pressure between the valve and the wheel cylinder?

[_Ogre]

a typical mc fitting doesn't seal with the threads, he may have used an incorrect fitting.
there should be an inverted flare inside the mc, you will need the correct fitting to plug it off.

like orrieg said, it's a no no to use teflon tape on brakes or any hydraulic system for that matter.
little strands of teflon floating around in residual valves, calipers or the mc can raise havoc.
your ''mechanic'' should know that, find a new one or at least have a sit down with him

[OrrieG]

Yes, disc pads rest right at the caliper and take little fluid to engage (that is why they have the smaller line and MC volume). Without the check valve the fluid bleed back and you have to pump to get the brakes to work again. Back drums are not as critical but still needed to keep fluid where it should be. Ogre got it, sound like they messed up the flare or used the wrong fitting, threads just press the flare to the inverted to seal.