[Chief of the 60's]

I think its funny how people on this forum will argue a point that something does not work with people who have done it and it does work no matter what the topic.

[Sirrotica]

Originally Posted by Chief of the 60's

I think its funny how people on this forum will argue a point that something does not work with people who have done it and it does work no matter what the topic.

The gotcha moment, it's well illustrated in everyday life.

The whole point of the thread was to illustrate that the gravity bleeding method, does work, it requires no special tools, you can do it in your backyard (I did), and is quick. Most people that make their living wrenching, use it.

I wasn't looking for criticism of the method, but I got it anyway........

Now we are into criticism that the gravity method doesn't remove all the accumulated sediment for flushing purposes. Sorry, from my vast experience neither does the 2 person method.

As Ben has said, I also usually run the fluid until it runs clear, remove a bleeder, if I happen to be bleeding it at a bleeder, and clean it out if it had no cap on it, probably 75% of the stuff I see, either never had a cap on it, or it's missing. I've had bleeders that were so corroded that no fluid flowed out until you completely removed the bleeder, and ran a drill through it to open it back up, fairly common in the rust belt where I live.

If a customer pulls in that just popped a brake line on a 1995 truck, with 220,000 miles, and wants it fixed so he can be on his way ASAP. I'm going to try to work him in to my schedule because it's high priority that he gets fixed, and on his way.

Am I going to talk him into a fluid flush of the system, hell no! The bleeders may become a huge liability. I'm going to do exactly what I did. Disturb as little of the system as I can, because it's old and corroded, but make sure the vehicle is safe, and that there is no air in the system. Gravity bleeding works splendidly for this purpose. Did I mention I was by myself?

The value of said vehicle is probably $2000, if that, (I only paid $500 for it), so is he going to want the complete system flushed and evaluated on a vehicle that works properly? Other than a weak brake line that is leaking due to salt accumulation on the exterior of a brake line, corroding a hole through the line, it is fine for the intended purpose.

We're not working on a Lamborghini here, it's a chevy work truck that's 25 years old, has a finite life, with an owner that has a finite wallet. In the rust belt the bleeders don't just unscrew, that is the exception to the rule if they do. Most every one is a fight to break loose from the caliper, or wheel cylinder without snapping it off. Lots of tricks to get them out, but they don't always work.

A hollow fastener that is welded by corrosion into the casting is no picnic to get out. Been there, done that so many times, I wouldn't even guess how many I've removed, and how many have snapped off.

I already made it crystal clear that I was by myself, so flushing the system using the 2 person method wasn't a real possibility anyway, even if I wanted to.

Reading comprehension is important, common sense is important, without this a mechanic doesn't survive. Just a reality check here.

[1968GTO421]

My thanks to Sirrotica for posting this and starting this thread. I've been confused for years about the best way to bleed brakes: gravity bleeding vs two people vs vacuum pump vs yet another gizmo.
This confirms my suspicion that gravity bleeding will do the job perfectly. Thanks!

[grandville455]

So All A guy needs to do is open a back bleeder and just pump the pedal at the top of the stroke a little to get a vacuum effect going then let it bleed out some , making sure master stays full?

[ta man]

Originally Posted by grandville455

So All A guy needs to do is open a back bleeder and just pump the pedal at the top of the stroke a little to get a vacuum effect going then let it bleed out some , making sure master stays full?

I learned that when you open a bleeder when gravity bleeding take the top off the master cylinder..it seems to flow easier. Just remember to put it back on.

[68lemans462]

Originally Posted by grandville455

So All A guy needs to do is open a back bleeder and just pump the pedal at the top of the stroke a little to get a vacuum effect going then let it bleed out some , making sure master stays full?

I'm wondering about this too.. ? I've had mixed results with gravity bleeding but have never worked the pedal when the bleeder was cracked. Also, do you usually start with the wheel cylinder furthest from the Master cyl?

My Pontiac has one of these disc brake hold off valves. Does the button on this need to be depressed in order to properly gravity bleed?


Great post!! thanks for the info

[Sirrotica]

Originally Posted by grandville455

So All A guy needs to do is open a back bleeder and just pump the pedal at the top of the stroke a little to get a vacuum effect going then let it bleed out some , making sure master stays full?

Darby, you pretty much said it.

If you've ever siphoned gas, it works on the exact same principle once you have fluid below the master cylinder reservoir level, your work is done. Gravity takes over from there. The small pump at the very top of the pedal travel gets the fluid running downhill, without drawing in air to the system. Atmospheric pressure, and gravity power it.

When done check to see if you have a firm pedal, if not open the bleeders and let it drip for a few more minutes. The procedure works because air will rise to the top of a fluid column, this bears out when you stroke the pedal while observing the reservoir. You'll see bubbles come up from the bottom of the reservoir if the lines have not been fully purged of air. You actually bleed an empty system from both ends using gravity bleeding. If you don't observe any more air in the reservoir, your most likely done. The rest of the air exits from the bleeders during the siphoning process.

It's a simple principle, yet some people make it overly complex.

[Sirrotica]

Originally Posted by 68lemans462

I'm wondering about this too.. ? I've had mixed results with gravity bleeding but have never worked the pedal when the bleeder was cracked. Also, do you usually start with the wheel cylinder furthest from the Master cyl?

My Pontiac has one of these disc brake hold off valves. Does the button on this need to be depressed in order to properly gravity bleed?


Great post!! thanks for the info

It actually doesn't make any difference what bleeder you open. If I replaced a rear brake line, typically I just open both bleeders in the rear and let them drip. Obviously the shorter tubing will fill first. Sometimes when speed is the essence I would just bleed the lines at the connection of solid line to flex hose, as I did at the beginning of this thread.

One other thing is, if you're dealing with a failed line, the spool in the valve may have shifted over center, and shut off half of the system, it also illuminates the brake warning light. In the case of a valve with the rubber boots on the ends of that valve you need to manually center that valve before attempting gravity bleeding.

Sometimes you need to deduce what is the best route of action. In my case the 25 YO truck needs brakes to move it around my yard, I'm not really interest in struggling with stuck bleed screws. I bleed it at the end of the line instead of trying to open the bleeders, and opening a can of worms if they are stuck. My life has been full of working on old rusty stuff due to where I live, getting the job completed, and saving time, and money figures into the equation if you're making a living from the craft.

I take the end of my finger and put it on the bleed screw restricting it so I can see the fluid as it exits. If there is still air bubbles coming out, or it's solid fluid exiting. When it's just fluid exiting time to tighten the screw up, go to the other side and observe the same. 99 out of 100 when you have no air exiting, you're done. I always then test the pedal firmness and travel. If I'm satisfied I then road test it, if satisfied with the road test your mission is complete.

I'm not familiar with the valves you posted. If it were me I'd try to blow through it with your mouth to see if it was open under no pressure situation. If it's open then gravity bleeding can commence. The other way to test it would to be start the siphon, and see if fluid will flow through it, if not your going to have to release it manually.

[grandville455]

Originally Posted by Sirrotica

Darby, you pretty much said it.

If you've ever siphoned gas, it works on the exact same principle once you have fluid below the master cylinder reservoir level, your work is done. Gravity takes over from there. The small pump at the very top of the pedal travel gets the fluid running downhill, without drawing in air to the system. Atmospheric pressure, and gravity power it.

When done check to see if you have a firm pedal, if not open the bleeders and let it drip for a few more minutes. The procedure works because air will rise to the top of a fluid column, this bears out when you stroke the pedal while observing the reservoir. You'll see bubbles come up from the bottom of the reservoir if the lines have not been fully purged of air. You actually bleed an empty system from both ends using gravity bleeding. If you don't observe any more air in the reservoir, your most likely done. The rest of the air exits from the bleeders during the siphoning process.

It's a simple principle, yet some people make it overly complex.

Thanks! So when u barely pump at the top of the stroke it doesn’t pull air back in like if push all the way to the floor when bleeder is open! I may try again today on my truck , have good fluid at back Bleeder but u can see bubbles in master yet when I pump the pedal

[1968GTO421]

I like the gravity bleeding. One question- my GTO has discs in the front, I see no problem there. On the back are factory drum brakes-what kind of problem to gravity beeding is the residual line pressure valve in the line. Any ways to work around this? Thanks.

[Sirrotica]

Originally Posted by 1968GTO421

I like the gravity bleeding. One question- my GTO has discs in the front, I see no problem there. On the back are factory drum brakes-what kind of problem to gravity beeding is the residual line pressure valve in the line. Any ways to work around this? Thanks.

There was a post recently on here, discussing residual line pressure on 4 wheel drum cars. The thought was that the siphon could overcome it. I've never run into any problems gravity bleeding a disc/drum car, or a 4 wheel drum car, and almost every older GM car has the residual valves on the drum cars.

[tallrandyb]

Originally Posted by Sirrotica

Mike, it would be better yet if you had a product that changed color to let you know when it should be changed. Identify when the water content was above a certain point.

If I remember correctly there are some test strips to identify when it should be changed, but I'm not certain that's correct. I could be thinking of coolant PH straps.

I do know there are millions of vehicles that are on the road that have their born with fluid still in the system years past thev3 year suggested time frame.

Used to be a German brake fluid in blue and tan; bleed until new color shows up, done! I loved it when on road courses with my 94 Pontiac.

I believe they stopped making it based on something about being able to identify what fluid was leaking from a car/part? Different color coolants but I guess that’s not so hard to identify.


Sent from my iPad using Tapatalk

[tallrandyb]

Originally Posted by mgarblik

Brake bleeding is always a fun topic. Like Sirrotica, I work alone 95% of the time. Gravity bleeding works great nearly all the time. I have a venturi style vacuum bleeder as well. To save time I often use it to start the bleeding procedure faster, especially in cars with ABS where fluid to the calipers passes through the ABS modulator first before getting to them. Vacuum speeds the process. Once flowing fluid, I remove and let it gravity bleed. I have XM radio in my shop and listen to the 60's mostly. Once the fluid is flowing, I let each wheel gravity bleed 2 songs, about 6 minutes each. That gives me a great pedal almost every time. Some vehicles with ABS can be a bear to get the air out of if the system has gone dry. (ABS modulator). Some have bleeder screws on the unit, which helps. They can be gravity bled. Some don't. The scan tool in bleed mode really just energizes all the valves and solenoids in the ABS unit and helps vent any tiny air bubbles to the MC. I have had some GM trucks I had to scan tool bleed 6 cycles to get a nice pedal. Changing brake fluid is a good idea as it absorbs water. I change fluid for customers all the time. ATE now sells brake fluid in 3 colors, Amber, green and red I think. You suck out the MC and put a different color fluid in the MC. Then when you bleed the brakes at the wheels, you look for the color change to know you have the old stuff out. Kind of a neat idea.

I didn’t know ATE had 3 colors, I’ll need to check that out thanks!


Sent from my iPad using Tapatalk

[Cliff R]

WAY back when I went to school for brakes they told us that gravity bleeding is the most effective, but also takes the longest. Start at the caliper or cylinder furthest from the master cylinder and crack the bleeder, then move on from there until all four are done. Just make sure to keep fluid in the reservoir the entire time and you'll be fine.

I have ran into a few applications over the years that didn't do well gravity bleeding alone but for most it's the best method if you get good flow and have the time for it.

IF you are using the brake pedal to help things out make sure to only move it a very short distance and not all the way too the floor or further than it's typical range of travel. A LOT of crap can be built up under it, and if you push the pedal down far enough to get into it you may find yourself replacing the master cylinder.......Cliff

[78w72]

ive never really read or heard anyone say gravity bleeding doesnt work, ive done it & learned from a friend thats been a mechanic for 35+ years that likes to do it that way most the time. it works.

my only thing after doing it both ways is that on a nice restored car with pretty paint on the calipers & a-arms etc that gravity bleeding makes a mess & brake fluid will strip or damage almost any kind of paint. i have friends & family members that can help do it manually & you can watch the line or jar to know when its really fully bled, even after gravity bleeding i have still seen small bubbles when doing it later manually but the brakes still worked ok with some small bubbles. its just so much cleaner & very simple to do it manually or use a vac bleeder IMO. if youre by yourself or in a shop rushed for time or stuck bleeders etc then by all means use gravity if you dont care about paint, or just buy yourself a mighty vac, it has many other uses & well worth the money.

[track73]

I have changed master cylinders and after bench bleeding them installed them and never had to bleed the system.

[Chief of the 60's]

Originally Posted by track73

I have changed master cylinders and after bench bleeding them installed them and never had to bleed the system.

Its suppose to work that way. Doesn't always though.

[tooski]

I recall having to change the master cylinder on an older ford pickup. Swapped out old for new. Hooked the lines up very loosely to the new master. Filled it and watched the fluid ooze out of the fittings. Tightened up the fittings and good to go. I expected to have to bleed at every corner. At the time I had not heard of the requirement for bench bleeding.

[Schurkey]

Gravity bleeding? Sure. I do it most of the time.

Sludge/crap/garfelderfarb in the wheel cylinders? Sure. Pull 'em apart, clean 'em out. I do this fairly often as the need arises on my various vehicles. In fact, most recently last week.

Iron calipers are "easier" than aluminum calipers. I learned about aluminum calipers on my Honda motorcycle. They corrode behind the square-cut seal. This creates a layer of aluminum "rust" which squeezes the seal into the piston, making it difficult to move. At worst, it locks the piston so it cannot move at all.

Here's photos of my left rear aluminum Trailblazer caliper. Piston was not seized, but it was very stiff. The dust seal and square-cut seal grooves were both corroded. I scraped the corrosion out with a pick. Cleaned both rubber seals with rags, and scraped the dreck off the square-cut seal with my fingernail. Polished the piston on a wire wheel. The photos of the cleaned-up piston look worse than it really is. Put the same seals back into the cleaned-up caliper. Piston moves freely. Doesn't leak. The only part I bought was a bleeder screw. Note the scuzz build-up on the piston, right where the square-cut seal rides.

[Schurkey]

The piston goes back in the same way it comes out--with compressed air. Use a piece of wood to "pad" the caliper when blowing the piston out, it will pop out with substantial force--enough to break your fingers if you try to "catch" it. (Rarely--the piston is so locked-up that 100+ psi of air pressure won't move it. Thread a grease zerk into the caliper, pump it with a grease gun--2000 psi will move the piston out.)

On the way back in, you "inflate" the rubber dust seal over the bottom of the piston. Its a balancing-act, you need to use enough air to pop the dust seal over the piston, but not so much air that you can't push the piston into the dust seal with your fingers. Once the dust seal is over the bottom of the piston, the piston will push past the square-cut seal with finger pressure.

The same ol' piston, on the same ol' seals glides into the caliper so lovely compared to the force needed before cleaning out the seal grooves. Yes, you're seeing anti-seize on the threads of the bleeder screw. The original bleeder screw needed oxy-acetylene encouragement to come out.

I might not do "no new parts" caliper overhauls on customer vehicles. I'm perfectly comfortable doing them on my own vehicles, though. So far, success rate is 100%. Iron calipers are "easier" in that the seal grooves don't corrode so readily. But the square-cut seal still develops a "crust" that needs to be scraped off, and the pistons always have a build-up where that seal rides that makes them high-friction.