Yes Tom I did mean 38 …… I’ll look today at a spare more carefully and see if I can add to this discussion ….at the moment all I know is that it works!
I might be. It’s been a few years since I last worked on the reaction valve, and memory is the second thing to go.
I wouldn’t suggest using anything abrasive unless you’re planning to disassemble the master. Otherwise you’ll leave some particles inside, which will surely do mischief.
Tom,
You may well be correct. I’m not sure whether pushing on the surface that the spring acts on actually results in any “push” being transfered to the intermediate piston in the head of the master cylinder. If not, then I presume that the only force acting on the piston when the brakes are released is from the Diaphragm Support (#33) being pulled back by the diaphragm due to the vacuum on the rear side of the reaction valve. I probably need to take one apart to understand it…
I believe it is the remaining portion of atmospheric pressure left in the booster chamber after the atmospheric air valve has closed that pushes on the diaphragm pushing the small piston back into the mc. Once the diaphragm moves far enough to open the vacuum valve, vacuum fills both sides of the diaphragm and both it and the small piston stop.
So to your statement, yes.
I know, vacuum is not doing the work and vacuum does not fill an area, air pressure does but I believe it is easier to describe this way.
Tom
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John, the gold polishing kit is comprised of rubber impregnated with different grits. They are not the stone kits. Brown is more course, then green and light green as the least coarse. They are not aggressive at all. Use very slow speeds and all they will do is eliminate any internal friction from the walls of the cylinder…
Regards,
Allen
thanks
Would anyone be able to post a photo of what the reaction valve (#38) spring looks like?
When I restored my car a few years ago I did not have one and put in what ever I could find. I have not been able to find a OEM one and have a similar problem to the poster (anyone have a spare?).
Pat
Well, I dug out my spare reaction valve. I’m pleased to say that I was correct. The spring ulimately increases force on the small piston. So the memory works, good for me. I’ll post some photos tonight, if I remember
.
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Surely it does, given the fact you found your spare reaction valve… 
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Michael. As i said i do not yet see that would you explain
Tom
Man, my memory is working today.
First, an apology. The cap is glued onto my spare reaction valve, so I’m not going to take it apart to reveal the spring. Sorry, spring fans.
I’m not sure why there’s any question that the spring applies force to the small piston. The way this works is that the small piston extends and hits the center rod of the diaphragm hub. This pushes the hub up into the valve mechanism and compresses the spring. The valve has two rubber poppets (41 and 34 on the diagram), connected by a spool. The first poppet closes off the center hole in the diaphragm, which prevents vacuum from being transmitted to the rear section of the booster. The second poppet opens the air bleed, which fills the rear section of the booster with air at atmospheric pressure. Sooooo the center section of the diaphragm is what compresses the spring, and it’s the spring that forces the small piston back when pedal pressure is removed. Photo essay:
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Michael, what you say is fine up to a point. I will continue with the valve having opened and bleeding air into the back of the booster. Now, when one releases foot pedal, thus mc hydraulic pressure, the spring will push back the valve, which will push back the diaphragm and its center poppet, which will push back the small piston. Actually, this is only partially true. The majority of the force pushing back is not the spring, but air pressure on the diaphragm. But either way, we need to continue. Yes, the spring is pushing on the valve. But as soon as the atmospheric air portion of the valve seats and shuts off the outside air, the valve can no longer move any further. Thus the spring can push no further. But the vacuum valve portion is still sealed. The diaphragm and its poppet must move further back to open the vacuum valve. The remaining air pressure in the booster, that has now been sealed off from atmospheric air, now alone pushes the diaphragm and its poppet away from the now stationary valve to open the vacuum valve readmitting vacuum to the back of the booster. It is only this remaining air pressure that moves the diaphragm and poppet which pushes the small piston back this last and most important distance, the last bit of distance to allow the remaining air pressure in the rear booster chamber to be evacuated and to fully release the brakes.
Thus I do not see how a stronger spring will help to move a sticky small piston back the last distance to open the vacuum valve.
May be to somewhat clarify we are dismissing details. Yes the spring does add force to initially push back the valve and diaphragm and poppet and small piston. But as I have said from the beginning, it does not push it back all the way to open the vacuum valve, which is what releases the brakes.
Tom
That’s reasonable. The valve needs to crack open for vacuum to be restored. So air pressure accounts for the last fraction of a mm.
I read that. While I don’t understand it well enough to explain, I do understand what you are saying conceptually, and it makes sense. I guess one could put a spring in so strong that it would push the diaphragm and piston, or is that impossible due to back pressure until the booster is empty? Do I have this right?
I think a good cleaning, bore cleaning and maybe the red rubber grease should help me. Easy enough to do and least invasive and altering of factory design.
I really think most stuck reaction valve issues are stuck small piston issues. The only thing that might stick in the reaction valve is the plastic hub as I pointed out in the photos. A more likely reaction valve problem would be failed rubber seals, which should be obvious with visual inspection.
A simple question all, from what I have learned there are two new MC’s available. Locheed (Aftermarket?) and Lucas.
Simply put, which one is best?
Thanks, Pat
I’m sorry to be a skeptic. But I think both are just names pressed into the aluminum. Although the successor company to Lockheed is still around, I think all of these are made “elsewhere.”
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In my mind, no, because the spring can only push the valve, diaphragm, poppet and small piston far enough to close the atmospheric valve, but at that point since that valve is now seated, something else must push the diaphragm, poppet and small piston a little further to open the vacuum valve.
Tom
Agreed, and the problem I believe we are all addressing is how to keep it free. And although we know many have this basic problem is it the same problem? Many report it is heat related. I cannot imagine the heat is causing enough dimensional changes in the metal to cause it to stick and not seize. Are the rubber seals heating up and either expanding or getting sticky. Is the dirt everyone finds heating up and getting sticky?
As to the spring, I have stated I do not see it as pushing the small piston that last bit, but does it affect things in another way? I currently do not see how. I know at least one said a stronger spring helped, but only for a while. Coincidence???
Tom