I have gravity bled my new brake fluid a few times now and I still have the spongy pedal feel. Does pressure bleeding remove more air bubbles than gravity, or is pressure bleeding solely for the faster speed of draining the fluid? I want to try all the cheaper alternatives before I assume it is a faulty master cylinder. My Mercedes manual does call for 30psi bleeding and does not mention gravity bleeding at all...
Does pressure bleeding remove air more effectively
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If Mercedes says 30psi bleeding...its for a reason. Yes, pressure bleed it.
Under pressure the fluid moves faster. If there are any tiny air bubbles, they're less likely to be able to move against the flow or hang in place. I expect this is what they're after.
On some cars (I don't know if this applies to yours) it is very difficult to bleed out air from the brake hydraulic system using just gravity or lower pressure. Opening the bleeder simulates a rupture and flow to that circuit is restricted. This is a safety feature.
On some cars (I don't know if this applies to yours) it is very difficult to bleed out air from the brake hydraulic system using just gravity or lower pressure. Opening the bleeder simulates a rupture and flow to that circuit is restricted. This is a safety feature.
gravity bleeding will not rid of air bubbles.
Vacuum bleeding, when done improperly, will risk the introduction of more air into your caliper(s).
Pressure bleeding, when done properly, will be just as effective as vacuum bleeding(when done right). Trick is, don't let the pressure bleeder run out of fluid.
After so many years of tial-n-errors, I can say that both (vacuum and pressure bleeding) can work beautifully if you know what you are doing.
Q.
Vacuum bleeding, when done improperly, will risk the introduction of more air into your caliper(s).
Pressure bleeding, when done properly, will be just as effective as vacuum bleeding(when done right). Trick is, don't let the pressure bleeder run out of fluid.
After so many years of tial-n-errors, I can say that both (vacuum and pressure bleeding) can work beautifully if you know what you are doing.
Q.
Originally Posted By: yonyon
Under pressure the fluid moves faster. If there are any tiny air bubbles, they're less likely to be able to move against the flow or hang in place. I expect this is what they're after.
On some cars (I don't know if this applies to yours) it is very difficult to bleed out air from the brake hydraulic system using just gravity or lower pressure. Opening the bleeder simulates a rupture and flow to that circuit is restricted. This is a safety feature.
Good point.
Under pressure the fluid moves faster. If there are any tiny air bubbles, they're less likely to be able to move against the flow or hang in place. I expect this is what they're after.
On some cars (I don't know if this applies to yours) it is very difficult to bleed out air from the brake hydraulic system using just gravity or lower pressure. Opening the bleeder simulates a rupture and flow to that circuit is restricted. This is a safety feature.
Good point.
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