Can someone please explain to me how this could work? Let’s say I disconnect the banjo bolt at the caliper of a car. Air is introduced and will inevitably float upstream (read: at a higher point than the caliper). Seems to me that no amount of fluid dribbling down at the caliper is going to force an air bubble DOWN to the caliper bleeder? This seems to defy all logic unless I’m missing something?
Gravity bleeding brakes
- Thread starter eric8
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edyvw
$50 site donor 2025
Never do that. Use a pressure pump or OBD to force the ABS module to push it out.
I understand how the column of brake fluid moves down with gravity. What confuses me is that the bubble of air will always remain above the column of fluid as it moves down. Thus, never allowing the air to make it to the bleeder screw.
When you say pressure pump you’re referring to something like a Mitivac?
For 50 yrs I have gravity bleed my vehicles that have the master cylinder above the calipers.
To cycle fluid thru the abs module use a 2 way obd2 scan tool
or
I can go out on the country roads where I live and do a few panic stops
To cycle fluid thru the abs module use a 2 way obd2 scan tool
or
I can go out on the country roads where I live and do a few panic stops
So you do an initial gravity bleed, go do the panic stops, then a final gravity bleed?For 50 yrs I have gravity bleed my vehicles that have the master cylinder above the calipers.
To cycle fluid thru the abs module use a 2 way obd2 scan tool
or
I can go out on the country roads where I live and do a few panic stops
speed bleeders are awesome
When you attach a hose/tube to bleed screw run the hose up a few inches and then down into bottle to collect old fluid, brake fluid will push thru and bubbles will come out and stay in the hose.
Isn't that exactly what happens? I've replaced calipers, and bled them by attaching a clear hose to the bleeder.... When I take off the reservoir cap the fluid slowly moves down and fills the caliper, pushing all the air that was previously in the caliper out with it. I can see whatever air bubbles there are coming out with the fluid.
My preference is to bleed using my Motive bleeder, but I don't have an attachment to fit it on cars with the traditional style square reservoir cap (my Fiero for example). So that car gets gravity bled.
I've had it work just fine on my 1999 STS. #1, Don't remove the banjo bolt, #2, slip a clear plastic hose over the bleeder valve on each brake caliper. #3 the other end of the clear plastic tube is inserted into a glass jar, with enough clean brake fluid in it to cover the open end. #4, Starting at the furthest caliper, open the bleeder and let the old fluid come out.
If you have a helper, they can make sure the reservoir stays full for you. Never let it go empty.
If you have a helper, they can make sure the reservoir stays full for you. Never let it go empty.
You can gravity bleed ABS equipped systems???
I see what you’re saying. The bleed screw is the high point on the caliper, but all you’re bleeding is the air bubble that’s trapped behind the piston in the caliper.
When you replaced the caliper, you also disconnected the banjo fitting, which introduced an air bubble upstream of the banjo fitting through the flex hose that migrated toward the engine bay. This is the air that I’m referring to. How would it ever make it down to the caliper bleeder?
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Gravity bleeding is like watching paint dry.
Use a pressure bleeder, or a vacuum bleeder.
Use a pressure bleeder, or a vacuum bleeder.
Gravity bleeding is the same as pressure bleeding but uses only the head pressure of the fluid. It probably wouldn't be suitable if there is air in the system but I've been doing it successfully for years on routine fluid replacement where no air should be introduced. The advent of low viscosity brake fluid has made gravity bleeding a more realistic proposition and a hot day helps too. The negative is it's time consuming particularly on the rear brakes. It works quicker on my motorcycle because the fluid head is greater and the brake pipe length shorter.
If that was the case, wouldn't all the air in the new caliper also migrate upstream towards the reservoir?
So is it your thought that any air bubble upstream of the caliper is being continually forced upward by the fluid moving down to the bleeder screw? Thus eventually being expelled as bubbles in the master cylinder reservoir?
You can do a gravity flush, but not gravity bleed. You need pressure to push down the air bubble.
Not all of it. If you remove a caliper piston and look at the relationship of the brake like entry and the bleed port you’ll see that as the area behind the caliper piston fills up with fluid, an air pocket will inevitably be trapped at the caliper bleed port
