Quote:
Originally Posted by Geoff
Shiny,
You have nailed it: the fluid cannot pass the check valve under gravity. The design of CVs varies as per brand, but the easiest to visualise & understand is the GM dual m/c where drum brakes are used. The CV is a simple rubber tip with a small spring that pushes the rubber into the brass outlet fitting on the m/c. No fluid exits until the spring pressure is over come, by some force on the push rod.
Pontiac Jim.
Later cars with disk brakes do not use a check valve [ & even some drum braked cars ], so these can be gravity bled.
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Please read how a residual check valve works from the ASE, in their study guide for ASE tests, it's in the last paragraph:
https://www.freeasestudyguides.com/r...eck-valve.html
As I reiterated over and over, and Jim said the exact same thing, when there is zero pressure in the system, gravity bleeding works just fine. My actual experience, over your theory, especially when the theory is inaccurate.
It allows fluid into the system UNTIL the pressure is reached where it shuts off the flow maintaining a slight pressure in the system. With no pressure. the valve is OPEN allowing fluid flow.
Sorry mate, the ASE shoots down your theory. I'd be much more inclined to believe the ASE than you. This explanation from ASE, and my previous experience, "nails it".
If you want an example, just find a system with a residual valve and release the pressure. See if it doesn't flow without pressure in the system. Since I've done it untold times I can tell you what the result will be. Fluid will flow unimpeded, as long as there is zero pressure in the system, which is what happens with gravity bleeding. If you leave the system open it will empty the master cylinder completely.
Just as I asked you in previous posts, "If I cut a brake line on a residual valve system, will it empty the master cylinder"? You never answered the question, but posted shop manual explanation that said with pressure bleeding the valve would have to be overcome. Well apples and oranges because I wasn't talking about pressure bleeding, so the shop manual (which never acknowledges gravity bleeding) says you have to overcome the pressure activated residual check valve..............
