There is lots of stuff on here about how to bleed brakes. One of them is to gravity feed. I can not find anywhere any details on how or why this works. Does the slow leak make the air go out at the wheels or does the air travel backwards and exit the master cyl. I am working on doing this now and I guess the real truth is if it works then it works, but I sure would like to know how? Many thanks in advance for all the help......
The fluid flows to the lowest point while the air travels to the highest. So what happens is any air in the wheel cylinder or caliper will float up to the open bleeder and be pushed out by the gravity pressure of the fluid. Air in the Master will tend to also be displaced by the fluid and escape through the master. Depending on the system this can work fine. It there are lots of curves or high and low spot sin the lines, air may still be trapped. Works great on motorcycles though.
Some guys on some boards swear by the method but until I got on the net on a regular basis a few years ago I had never heard of it and I did brakes for a living for a number of years. It seems to be something that amateurs with a lot of time on their hands like to try. I know that some of the proponents of doing it that way will scream at me but If I had ever gravity bled a set of brakes in a shop I worked on I'd have been canned on the spot. You can build your own pressure bleeder using a one gallon weed sprayer for under 20.00 but would have to make a cap for the master cylinder or adapt one. http://faculty.ccp.edu/faculty/dreed/Campingart/jettatech/bleeder/index.htm
Gravity bleeding can be helpful when manually bleeding on a new dry system, and with the master cylinder located higher than the wheel cylinders. (If you're going to use a pressure bladder, it's a waste of time). The process is slow, and you have to monitor the master cylinder fluid level, but it will get some fluid into/air out of the system and make the mandatory normal bleeding easier. Open one bleeder at a time, and when fluid appears, close it and move to another.
ive done this many times... it works best when starting with a dry system... i will fill the master ,open the bleeder farthest from the master,,after it starts dripping i move to the next one and then on...i ALWAYS bleed it the manual way after that...
Gravity sometimes will flow, but many times it just won't flow...Design differences in different cars? or like was said about empty lines? maybe a line full of trapped bubbles can stop the gravity? I do bleeding by myself; I never bench bleed. I bleed at the master output line fitting after replacing a master. Loosen it, then pump real slow and only a bit more than halfway down, then let the pedal back very slowly. Sometimes, you don't even need to bleed the rest, "if" the lines were full of fluid and you were just replacing a master that was leaking out the back. Then if the lines were empty, I open the closest bleeder to the master. Then very slowly, and only a bit more than halfway down, pump the pedal and let it up very slowly. It won't **** air back in if you do it slow. Do the other wheels the same. I started doing it this way to get around that brake warning light safety switch stuff. You are supposed to lock that piston so it can't shut off one circuit. Bleeding without any pressure in the lines, makes that a non-issue. It all sounds backwards to mechanics school, but I have not one car/truck that I could not bleed this way....and I do quite a few each year...mostly oldies, but some late model junk too clutch masters can usually be bled without touching the bleeder at all. You just lightly touch the clutch pedal, barely going past the rod freeplay. Each time you do that, you should see a bubble or two of air come up to the master cyl fluid resevoir....if that's too slow, just crack the bleeder a bit.
Based on an article in Car Craft magazine I took a 1/4 inch flat plate of aluminum large enough to overhang the master cylinder about an inch all around. I drilled then tapped for 1/4 taper pipe thread so I could put in a standard male air fitting. Using a flat gasket with a hole in it I clamp it onto the top of the master cylinder with a C-clamp. With a full master cylinder I plug on the shop air hose WITH ZERO PRESSURE !! Slowly I adjust the air pressure to 3 psi to 5 psi. Get under the car farthest away first. Put on a clear hose to the bleeder valve so you can see the air bubbles. Drain it into a 10 oz water bottle (again clear). Fill the master cylinder a few times and don't let it go dry. My Chrysler has power brakes and this method works great. Just did the wife's MGB last month. It has a screw on lid for the master cylinder. I had a spare master so I modified one lid. Drilled and tapped again, (had to be careful because it was plastic). This car has manual brakes, very stiff, but the car stops now. Both cars I replaced all the brake lines. I also have a Mitivac setup, which seemed to work fine, but I always felt it was ****ing air around the bleeder threads. The pressurized master cylinder method you can see when the air bubbles are out.
I take a high quality oil squirt can and put some clear hose of the right dia on the nozzle and fill the squirt can with brake fluid. Now you can bleed from the brake caliper or wheel cylinder. Put a loop in the clear tubing and you will be able to keep any air bubbles at the top of the loop and not pump them into the system. Works good on cars but works awesome on motorcycles.
Once you use a Phoenix style reverse bleeder, you will forget about the other types of Brake Bleeding. VR&C.
a large syringe from a large animal vet supply is how i do it now. i threw out all the others. fill the syringe with brake fluid, add a short 1/4" hose with MC cover off. now fill the system thru the bleeders. I no longer bench bleed master cylinders. just put them on and back fill I forgot to add, if there is any bleeding to be done after this I always gravity bleed!!!!
OK....great info here and thanks to all. I looked up the Phoenix system and that really looks great but 80.00 bucks for something that I hope to use only once in a year. I also looked at the home made air pressure deal. It looks pretty good as well. I will figure out something. THANKS Mark
That sounds like the home made version of the Phoenix system, I like it and will try this tomorrow. THANKS , Mark
For some reason gravity bleeding has a cult following. Someone always says they have been doing it since the beginning of time and there is nothing better. What I have found is; Gravity bleeding will get enough air, out of most systems, most of the time, to get by ok. Following gravity bleeding with manual, pressure, or vacuum bleeding will almost always expel some air that gravity bleeding left in the system.
I am looking for the NO AIR solution.....so I will probably skip the gravity thing and do the reverse bleed idea. THANKS
i always gravity bleed.well mostly always.but i follow up with the mityvac va*** pump.to keep air from p***ing by the threads,i brush a little anti-sieze on them, and only pump a little va***. i rember reading that years ago some model of(i know its ot) Renault was prone to airlocking during brake service,to remove air,elevate front end 2 feet and gravity bleed. after battling airlocks for years,usually after line replacement i tried gravity and success was good.
Yep! First time I gravity bled, it was by accident. After i cleaned the mess up, the final bleed was faster than a snap. I though I discovered some new trick. Now I do it that way all the time. Its just so much easier and so far I haven't found one that it hasn't worked on. Always follow with a conventional bleed to be sure.
I'll give it a try again, never had much luck with it in the past though. The trick to general bleeding is to have a sharp person working the pedal, from there it takes only 5 minutes. Bob
Easiest way to do it, runs $25. Get an extra bleed screw and drill it out, then use it so no air is ****ed around the threads. Have somebody refill the master and let fly. This works quite well for under floor masters too. http://www.harborfreight.com/brake-fluid-bleeder-92924.html
Applying air pressure directly to brake fluid is really not a good way to bleed a system, as performed above, or with one of the home made or store bought "garden sprayers". I know many see this as a cheap and easy way to bleed brakes and are happy with the outcome, but the result is forcing air into a system that you are trying to remove air from! The pedal may feel fine, but the bleed cannot be as good as one using fresh uncontaminated fluid. Brake fluid, especially DOT 3 & 4, should be kept isolated from air as much as possible, as it is hydroscopic (attracts water) by nature. Using shop air, depending on how well it's filtered, climate/location, temperature etc, can contaminate, in varying degrees, the fluid with moisture and oil, the two worst enemies of a brake system, along with lowering the wet/dry fluid boiling points. The reason professional pressure bleeders cost more than $19.95 is because the fluid is contained in an air-tight bladder. Air pressure acts on the bladder, NOT the fluid. If you're going to bleed brakes often, or just want the best method for brake bleeding (IMO ) the investment in a pressure bladder will be a good one. If the cost is prohibitive, I would stay with methods that don't inject air into the system. JMO
Right there is the biggest issue with bleeding brakes with someone helping, The helper, him or herself. My 32 year old daughter has been helping me bleed brakes since she was four and can get it right every time and it's quick and simple. With my wife pumping the brakes the battle is on as she won't listen. 1. the helper has to pump the brakes SLOWLY or they will get air back in the system. 2. They have to hold the pedal down until you tell them to pump it again. 3. You have to check and refill the master cylinder often so you don't run it dry.
I had a brake shop for 25 years and of course I was the pumper for my guys when it was bleeding time. We never used a pressure bleeder or any other fancy tool. I have never been able to get the gravity system to work for me. I recently replaced a rusted out brake line and had to have a buddy come over and pump the pedal after leaving it open over night. 3 pumps and we had a pedal. It was the last 3' on the run to the RR. It didn't work for me.
I always get the best results that way too, Tommy. But gravity will get me by, most of the time. Does anybody have any experience with the Bleeder Buddy? I saw someting about that recently on TV. But they can make anything look good on TV, even if it isnt... It looks like it could be exactly what I'm looking for, but I'd like to hear from somebody who's used it before I buy one.
Gravity works better the higher the master is. When I had to redo a rear line in one of my vans with that damn combo valve that makes it impossible to pedal bleed, I did it that way. Worked fine. If your master is under the floor, forget it, it's never going to happen. Basically just ran a hose off the bleeder into a jar and let it flow, and kept it full up top. I've even done it in emergency line replacement situations, just let fluid run into the new line until it was dripping, then crank it tight - not ideal, but it got me home.
Dynaflash, This Harbor Freight unit attaches at the caliper's bleeder screw ****** and pulls fluid from the MC to the caliper using a shop or home compressor. You have to unscrew the bleeder screw a turn or so to allow the fluid to flow, and by doing so some fluid may leak around the threads creating a mess. Scarebird suggests that you can get an extra bleeder screw, drill it out and use it during the bleeding process, and avoid this potential leak. This modified bleeder screw is screwed all the way in and there is no mess, yet it allows fluid to flow while using this tool. By drilling the bleeder screw out, fluid is not restricted and it's like having no bleeder screw in at all, except that the ****** of the bleeder screw is needed to attach the bleeder tool. After bleeding the caliper, just replace the normal bleeder screw and move to the next caliper. And, of course, make sure the MC doesn't run too low during the bleeding process. I don't know Scarebird, but he is an Aliance Vendor who deals with brake parts and I ***ume he knows what he is talking about. And like he mentioned, since this tool pulls the fluid towards the calipers, it will work with MCs under the floorboard (where residual valves might be a problem with "reverse bleeder" tools). I hope I explained this well enough. Regards, X
Yes, and Thank you. I do know Scarebird (not personally) and have used his brake kits before. They are good products and the price can not be beat. I just did not understand how you can bleed the brakes and then remove the bleeder screw and not get air right back in there? I guess if the bleeder screw is truely at the top and fluid is coming out while you are changing it then it may be OK but this is a Chev rear with the Caddie disc conversion. The bleeders are in the wrong position while on the car. I will remove the caliper and position the bleeder at the top and try this approach. It seems that everything is fine, but I just can not get a good pedal.
YOU just have to be real quick doing it. Or, have a guy push dead slow on the pedal, keeping a light pressure on the fluid, not allowing air in until you get the regular bleed screw seated.
The bleeders are in the wrong positionwhile on the car. I will remove the caliper and position the bleederat the top and try this approach. Doesn't matter what you do- or how fast you do it - or who is helping if that bleeder isn't at the top of caliper you will not get all of the air out of it. It's physics, and there's no changing that. Bleeder needs to be at the top, where the air is if you want the air out. Bleeding a loose caliper will be a bit of a challenge, make sure you have something close to rotor thickness in there, and square and in deep enough. If your hard line gives enough to position it, that is. Can't you trade the calipers left for right and get the bleeder up top. If it has got to be the way it is due to design restraints and mis-calculations at this point, think about having another bleeder hole machined at the top.
31 Vicky, this seems to be a standard when using the Cadie calipers on a Chev rear. It also seems to be the source of my troubles.....or at least I think so. There is a soft line going to the caliper so movement is not a problem, but I have now moved these calipers in every position possible and still have a soft pedal. I really do not believe there is still air in there but what else can it be? THANKS Mark
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