Master brake cylinder
 

While working on the fuel system and replacing rear brakes, I also replaced the 2 vacuum hoses associated with master.

Now after I turn off the car the brake pedal instantly becomes hard and I can hear what sounds like vacuum being released. Normal? And maybe the old hoses were leaking vacuum, or not normal? The brakes work great, so I don't want to fix something that's not really broken by digging into it. Thanks

Was this problem evident prior to you replacing hose(s)? What year is your car? You likely built this problem in by replacing hose from booster to intake manifold. It has a check valve in it to retain vacuum in booster on shutdown. I f the engine were to stall while driving,you would have 2-3 applications of brakes with assist before stored vacuum in booster was depleted. Hopefully you didn't toss oe hose...

Thanks, I kept the old hoses, but they are now in the attic, so I'll look once it cools down next week. Are you saying it's an internal valve that is part of the hose itself? I've seen others like the valve on the fuel line by the carb, but that one is not built into the line itself.

If it's molded into the line, do you know if those are still made? The hose was brittle and cracked, so it needs to be replaced.
Thanks

Booster losing vacuum on shutdown from lack of check valve is easy enough to check. With car running,pinch off hose with visegrips or hose pinching pliers and shut car off,what happens?

Thanks for the tip, I'll try it when I get home Wednesday.

FWIW,the check valve is inside the hose end where it attaches to brake booster.

I can feel something solid right here that is not the metal pipe. I'm glad this thread came up or I too would have thought it was just a rubber hose.
https://cimg4.ibsrv.net/gimg/www.rx7...1eb5b0f9da.jpg

I cut it out of my old hose and installed it in the new hose. If you aren't sure if the new hose has one, remove the hose and blow through it from both directions. It should only allow air to pass from booster to manifold, not the other way.

I'll snap a picture once I get mine out. Nice thing is it's not impacting car running brake performance.

I'm sure there's a number of 1 way check valve that can be inserted with a clamp on both ends.

You could do that,always an option,many do. I prefer to keep the original. Locate the valve,it will be at one end of hose at booster,on SE models it's located right at booster and the other 1st gens are often at end of hose where it attaches to vacuum pipe that comes across firewall.
Locate the valve by feel and use a fresh single edge razor blade and slice the hose open from the end up to and a little past check valve. Peel the hose open and away from valve and remove it. Pay attention to valve orientation,insert it into end of new hose using liberal amount of silicone spray to ease it in. Use something like a 3/8" wooden dowel to gently push it in the hose far enough to be able to install hose back on to pipe/booster.

Consider replacing valve sooner than later. An engine stall when you need to apply brakes will instantly lose any power assist-that you might not be ready for. If booster diaphragm were to fail,vacuum leak would be so large car definitely would not idle,will run poorly and possibly wouldn't start.

My SA has this valve as separate piece in my booster vacuum hose assembly and I'm pretty sure its OEM. Maybe this is for FBs only or series 3 only?

SA and other older models in Mazda lineup have external check valves in booster supply hose.
81-82 was changeover to internal check valves,on several other makes as well,