That is correct ! Ron

Just look at it this way. You can get a leak anywhere in the brake system. So if you have a line loose at the M/C and it leaks fluid then it has a leak before any fluid even gets to the safety switch or any valve in the system. You can loose all the fluid in half the system and its all lost before the fluid gets to any valve. You will still have half the brake system working with the lower pedal since fluid in the leaking system will cause the pedal to now be pushed farther down to compress the spring in the M/C and bottom out the piston. Don't matter what the valve does because all the fluid in the side that leaks never got to the valve as it leaked right at the M/C line. The safety valve will still move over because the working side will have pressure to move the valve over but the valve cant stop fluid from leaking since it all leaked out before the valve.


You will still have half the brakes with a lower pedal if it has a safety valve or not. That's the easiest way you can look at it and realize the safety valve had nothing to do with it since in that leak all the fluid would be lost in one side. Ron

I already have and I had half my brakes and the car stopped and I don't have a safety valve in my car. I even drove it about 8 miles like that until I could get some brake fluid. Ron

And that's wrong. With the safety valve installed you do not leak all the fluid and your pedal sits higher giving more of a safety margin than without.

Will you brakes "work" without a safety valve? Yes, for certain values of work, as long as you understand one of those values is not work properly, nor work as designed by an engineer.

Study this real well, 69 Plymouth manual. When that valve moves from a broken line, what does it cover up? It WILL move to SHUT off the port that's lost pressure.

99% of all line breaks are after that valve.

How does the fluid get between the separate, unconnected, pistons in the master cylinder? What keeps it there? Magic?

My wife said I was beating my head against a wall, I think she's right.

I hate to burst your bubble but its physically impossible for the pistons to move far enough to shut off either side. It CAN move far enough to actuate the safety switch though. Its a simple design. Nothing more than a hydraulically actuated switch.

I will guarantee you that is exactly what that valve does.


But don't believe me, open a bleeder and stomp the brake.

Why won't anybody do this?

If I designed a valve that could operate a switch, AND cut off a leak, why not both?

I would guess at this point, if some of you SAW proof of "no dual brakes" you couldn't believe it.

If you read the responses, 383MAN has already stated this happened to him and he had brakes in the other half of the system. AND he didn't have a safety switch installed. So that pretty much proves that your dual master cylinder provides braking to the good half of the system in event of a failure of the other half. Once again the SAFETY SWITCH is just that... a simple hydraulically activated electric switch. It shouldn't be such a difficult concept to understand. Perhaps this video will help those who insist this switch is more than it really is understand this concept. You'll have to understand... this video was made for training those dumb Mopar service technicians on dual brake system.

[video:youtube]https://youtu.be/14JZQ3W6qYg[/video]

The following video also explains what the brake safety switch does... but is geared more towards people who can read and write.

[video:youtube]https://youtu.be/1oI2yrRCUVI[/video]

Ron didn't have a leak at one end or the other, he had a bad master cylinder as I read it. As such, still had brakes.


Hey, I could be wrong, just gotta prove it.

Watch the videos above. They will explain how the system works.

Bill, I do feel a little guilty starting something then leaving the room, just hope to see the end of all ends for the answer to the outcome. Some great info here!

Actually the leak I had proves the valve has nothing to do with and I still having half the brakes working. I don't know why some cant understand that my leak was at the M/C rear resivoir which means no valve in any position stopped the fluid from leaking out because it all leaked on that's side of the system. Yet I still had brakes with a partial pedal and half the system and no valve in my system other then a prop valve in the rear line.


The point I am making is they are separate systems not hydraulicly tied together. They have fluid on different sides of the same pistons but not the same fluid since one can leak all its fluid and the other side can still work which it will. Which is why they went to the dual system in the first place. The fluid on either sides of the pistons are separated by the piston seals. The safety valve just warns the driver by turning on the light on the dash. The prop valve just keeps the rear brakes from locking on hard braking and the metering valve keeps the front disc brakes from applying until the rear brakes overcome their spring pressure. The combination valve just puts some or all of these in one valve on cars that need them.


I am not trying to upset anyone but it seems we all think and believe what we like and I can understand that. I said my piece and hope I did not make any body to ticked off as that's not the point of this. No sense in this going on anymore as we have all made our points. Ron

No you are not at any fault as I want to appoligize to you for us hijacking your post. Sorry as I don't believe that's what any of us meant to do. Ron

No apology needed Ron, some good information was gathered here!

Dan.