Master brake cylinder
#1
Rotary Enthusiast
Thread Starter
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
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
#2
ancient wizard...
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...
#3
Rotary Enthusiast
Thread Starter
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
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
#4
ancient wizard...
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?
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#9
Rotary Enthusiast
Thread Starter
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.
I'm sure there's a number of 1 way check valve that can be inserted with a clamp on both ends.
#10
ancient wizard...
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.
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.
Last edited by GSLSEforme; 08-20-19 at 10:07 AM.
#12
ancient wizard...
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,
81-82 was changeover to internal check valves,on several other makes as well,
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