So I'll be soon converting the 69 to front discs, 69/70 single piston style. I'll need a disc/drum master so I order one. Advertised as "Front disc brakes, power brakes". I like this style as it seems to approximate what would have been under hood if the car came with discs. The price is good and I know what that means, it means it's Chinese. Fine, and its got the "popular part" heart, so people must love it, right?

The package arrives. I open it up and immediately look to the line seats on this thing, and low and behold the brake line flair seats are machined as cast. 

Bad sign off the get go, if the seats are iron, the master has no residual check valves. And I'll still need one in the rear. Lightly probed with a paperclip, it's obvious there is no valve behind the seat. You can clearly see the cast iron seats below,

10 and 2 lb residual valves in a drum system originally served 3 functions. First, rectified in GM cars post 54, the mater resided under the drivers floor. The brake wheel cylinders were above the master, and as such would drain by gravity back to the reservoir. Second, the early designs of the wheel cylinder seals tended to draw or pump air back into the system when cycled too far too often, a 2 lb valve was used originally. And thirdly, as today, drum brakes tend to have a good amount of mechanical "take up" before the shoes contact the drum, this take up would be seen in excessive pedal travel. 10psi held in the line will hold the wheel cylinder pistons out at just the right spot, the same spot that you originally adjusted the brakes to. The residual valve takes care of all 3 issues. 10lb is the accepted pressure today. Discs need not have a valve, as the pistons will usually remain out at just the right spot allowing the pads to just kiss the rotor waiting for increased pressure. Some pro touring guys will say discs should have a 2lb valve for a faster pedal. But I don't think on the street we need it. I've done 2 conversions without it.

The tell tale is this, you usually will have a brass flair seat for it to have a residual valve fitted. It fits behind, then the seat gets pressed in. It can also sometimes be steel.

As cast, a valve cannot be fitted.

You can easily spot brass seats,

This is something you really need to confirm if you are installing any new master on a drum brake car. And as far as I can tell, this omission is rampant in these offshore masters. They rarely are as advertised. Sometimes you get a comprehensive info list describing the part, but I've not seen any description of "Check Valve = Yes" in them.

Now the fronts obviously will be fine, no valve required for a disc system, but I'm loath to return it seeing it's a pita. I think I might just buy a Wilwood 10lb residual valve and plumb it in along with the hold off valve. Paint it black and it might not look too out of place. 

The two lessons,

• Buy your new master locally, open the box and actually look at what you are buying. Confirm you have a valve or valves depending on your configuration. No valve, no thanks.
• Drum brakes 100% need a 10 lb residual valve. without it, you will have poor pedal (or any pedal at all) after bleeding.

Now, this might seem a lot of hullabaloo about this valve, but I know instances where brake jobs became a lesson in frustration, all because of the lack of this tiny little valve, and the lack of knowledge about it. I'll be honest, up until a couple of years ago I'd always just take it for granted that my replacement master would be correct and ready to install. Nope, not anymore.