Brake line inlet is in center of caliper and bleeder sits on top. When you are bleeding/flushing the brakes, it looks like there will be a dead spot at the bottom where old fluid will not be flushed out. Only way to completely remove old fluid is to depress piston with bleeder open. Am I right?
Flushing Calipers
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Originally Posted By: chad8
how about turning it upside down and letting fluid drip out or use a mityvac..
I suspect old brake fluid and fresh brake fluid have the same specific gravity so turning upside down would not make any difference inless you let the caliper drip until it was empty. At that point you would have introduced air into the MC which would be a PITA to remove. I have a vacuum bleeder. Using a vacuum bleeder, pressure bleeder or the old fashioned brake pedal pump doesn't have anything to do with the fluid flow pattern inside the caliper chamber. Problem with all three methods is that the low bleed flow is almost certainly laminar with little to no mixing inside the caliper.
how about turning it upside down and letting fluid drip out or use a mityvac..
I suspect old brake fluid and fresh brake fluid have the same specific gravity so turning upside down would not make any difference inless you let the caliper drip until it was empty. At that point you would have introduced air into the MC which would be a PITA to remove. I have a vacuum bleeder. Using a vacuum bleeder, pressure bleeder or the old fashioned brake pedal pump doesn't have anything to do with the fluid flow pattern inside the caliper chamber. Problem with all three methods is that the low bleed flow is almost certainly laminar with little to no mixing inside the caliper.
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Most calipers are designed with internal plumbing to route the fluid so that they can be bled while installed on the car.
As an example - I had 4 piston calipers on my 1985 Volvo Turbo. the internal plumbing routed the fluid to flush all 4 pistons, on both sides. There were 2 bleed screws. I once replaced a caliper and could not get it bled - long story short, the rebuilder had used a left outer half on a right caliper, and all the internal passages were upside down, so air could not be forced out...and I couldn't get a good bleed (this was not as simple to diagnose as it sounds...).
Bottom Line: Just bleed them, if they're OE, I am sure they'll bleed just fine.
As an example - I had 4 piston calipers on my 1985 Volvo Turbo. the internal plumbing routed the fluid to flush all 4 pistons, on both sides. There were 2 bleed screws. I once replaced a caliper and could not get it bled - long story short, the rebuilder had used a left outer half on a right caliper, and all the internal passages were upside down, so air could not be forced out...and I couldn't get a good bleed (this was not as simple to diagnose as it sounds...).
Bottom Line: Just bleed them, if they're OE, I am sure they'll bleed just fine.
I would truthfully just do the normal bleed method.
Even if a tiny bit of old fluid is left behind, it's no big deal.
Happens with oil changes, transmission fluid, etc. No harm done.
Even if a tiny bit of old fluid is left behind, it's no big deal.
Happens with oil changes, transmission fluid, etc. No harm done.
Originally Posted By: Astro14
Most calipers are designed with internal plumbing to route the fluid so that they can be bled while installed on the car.
As an example - I had 4 piston calipers on my 1985 Volvo Turbo. the internal plumbing routed the fluid to flush all 4 pistons, on both sides. There were 2 bleed screws. I once replaced a caliper and could not get it bled - long story short, the rebuilder had used a left outer half on a right caliper, and all the internal passages were upside down, so air could not be forced out...and I couldn't get a good bleed (this was not as simple to diagnose as it sounds...).
Bottom Line: Just bleed them, if they're OE, I am sure they'll bleed just fine.
Thanks. Yes, I know they will bleed air ok because the bleeder is on top. I was asking about flushing out all of the old fluid.
Most calipers are designed with internal plumbing to route the fluid so that they can be bled while installed on the car.
As an example - I had 4 piston calipers on my 1985 Volvo Turbo. the internal plumbing routed the fluid to flush all 4 pistons, on both sides. There were 2 bleed screws. I once replaced a caliper and could not get it bled - long story short, the rebuilder had used a left outer half on a right caliper, and all the internal passages were upside down, so air could not be forced out...and I couldn't get a good bleed (this was not as simple to diagnose as it sounds...).
Bottom Line: Just bleed them, if they're OE, I am sure they'll bleed just fine.
Thanks. Yes, I know they will bleed air ok because the bleeder is on top. I was asking about flushing out all of the old fluid.
artbuc - that's kind of my point - if they're routing fluid to force air out, they'll get almost all of the fluid too...
So, on the Volvo example, inlet in the middle, but fluid went to the bottom of the lower piston first, then up through the caliper to the bottom of top piston on the inside. It also went to the bottom of lower piston on the outside, then up through the caliper to the bottom of the top piston, then out the bleed on that side...(took 'em apart to see...pretty clever, really...).
To get the air out, you've got to move the fluid from bottom to top of the chamber behind the piston...you'll get almost all the fluid...
So, on the Volvo example, inlet in the middle, but fluid went to the bottom of the lower piston first, then up through the caliper to the bottom of top piston on the inside. It also went to the bottom of lower piston on the outside, then up through the caliper to the bottom of the top piston, then out the bleed on that side...(took 'em apart to see...pretty clever, really...).
To get the air out, you've got to move the fluid from bottom to top of the chamber behind the piston...you'll get almost all the fluid...
Originally Posted By: Astro14
artbuc - that's kind of my point - if they're routing fluid to force air out, they'll get almost all of the fluid too...
So, on the Volvo example, inlet in the middle, but fluid went to the bottom of the lower piston first, then up through the caliper to the bottom of top piston on the inside. It also went to the bottom of lower piston on the outside, then up through the caliper to the bottom of the top piston, then out the bleed on that side...(took 'em apart to see...pretty clever, really...).
To get the air out, you've got to move the fluid from bottom to top of the chamber behind the piston...you'll get almost all the fluid...
Thanks!!
artbuc - that's kind of my point - if they're routing fluid to force air out, they'll get almost all of the fluid too...
So, on the Volvo example, inlet in the middle, but fluid went to the bottom of the lower piston first, then up through the caliper to the bottom of top piston on the inside. It also went to the bottom of lower piston on the outside, then up through the caliper to the bottom of the top piston, then out the bleed on that side...(took 'em apart to see...pretty clever, really...).
To get the air out, you've got to move the fluid from bottom to top of the chamber behind the piston...you'll get almost all the fluid...
Thanks!!
You can bleed the air out perfectly, but you are right... it will not flush all old stuff out.
But this applies to ANY brake system. There are always nooks and crannies where some sediment/deposits reside.
Just bleed it right and be happy!
But this applies to ANY brake system. There are always nooks and crannies where some sediment/deposits reside.
Just bleed it right and be happy!
Originally Posted By: mechtech2
You can bleed the air out perfectly, but you are right... it will not flush all old stuff out.
But this applies to ANY brake system. There are always nooks and crannies where some sediment/deposits reside.
Which is part of the reason why you're supposed to replace the fluid every two years (or whatever your manual specifies)...
You can bleed the air out perfectly, but you are right... it will not flush all old stuff out.
But this applies to ANY brake system. There are always nooks and crannies where some sediment/deposits reside.
Which is part of the reason why you're supposed to replace the fluid every two years (or whatever your manual specifies)...
A simple gravity flush using vinyl hose on the bleeders & monitoring the reservoir level is a no brainer.
All 4 wheels can be done at once.
A simple one man job.
All 4 wheels can be done at once.
A simple one man job.
Can you explain a gravity flush? Forgive me, I am not familiar with the concept...I've always done the brake pedal flush (back to the 70s, when I first learned to work on brakes) and recently, bought a Motive power bleeder for the euro cars to save my lovely wife from having to sit and pump the pedal...
I do this on my car after track days.
Just put the car up in the air (or not if you can do it) and open the bleeders slightly. I put a hose on the car as the calipers are all painted pretty, but on my trucks I don't do nuttin'.
Simply keep the MC full, stop when you see clean fluid come out the farthest caliper.
Just put the car up in the air (or not if you can do it) and open the bleeders slightly. I put a hose on the car as the calipers are all painted pretty, but on my trucks I don't do nuttin'.
Simply keep the MC full, stop when you see clean fluid come out the farthest caliper.
Originally Posted By: Astro14
Can you explain a gravity flush? Forgive me, I am not familiar with the concept...I've always done the brake pedal flush (back to the 70s, when I first learned to work on brakes) and recently, bought a Motive power bleeder for the euro cars to save my lovely wife from having to sit and pump the pedal...
The general idea is that you can open the bleeder and fluid and any air will dribble out via gravity due to the fact the brake fluid level is higher in the brake system, and air won't go downhill back through the bleeder. It's really just a slower, lower pressure version of using a mightyvac at the bleeder.
One advantage of it besides being a one-man bleeding is you don't have to deep stroke the master cylinder which sometimes can cause internal sealing issues if only temporarily.
Can you explain a gravity flush? Forgive me, I am not familiar with the concept...I've always done the brake pedal flush (back to the 70s, when I first learned to work on brakes) and recently, bought a Motive power bleeder for the euro cars to save my lovely wife from having to sit and pump the pedal...
The general idea is that you can open the bleeder and fluid and any air will dribble out via gravity due to the fact the brake fluid level is higher in the brake system, and air won't go downhill back through the bleeder. It's really just a slower, lower pressure version of using a mightyvac at the bleeder.
One advantage of it besides being a one-man bleeding is you don't have to deep stroke the master cylinder which sometimes can cause internal sealing issues if only temporarily.
A gravity bleed is a low pressure bleed.
First, simply put a hose on the nipple and run in into a container [for later disposal].
Open the bleeder. Shut the bleeder.
First, simply put a hose on the nipple and run in into a container [for later disposal].
Open the bleeder. Shut the bleeder.
If you gravity bleed, don't touch the pedal or move any parts!
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