Gravity Bleeding
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More Turbo
Joined: Sep 2008
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From: Pennsylvania
Gravity Bleeding
I just got my new master cylinder/power booster, and once school's out and I actually have time again, I'm going to install it. Which, of course, means I'll have to bleed the brakes (again... 
). Last time, I worked the bleeder screws while my dad was at the pedal, and it worked alright, although not as completely as I'd hoped. I heard about gravity bleeding lately, could someone explain the procedure for that? It's okay if it takes a long time, once school gets out I'll only have a part-time job for at least the first few weeks, so time is something I got.
). Last time, I worked the bleeder screws while my dad was at the pedal, and it worked alright, although not as completely as I'd hoped. I heard about gravity bleeding lately, could someone explain the procedure for that? It's okay if it takes a long time, once school gets out I'll only have a part-time job for at least the first few weeks, so time is something I got.
Senior User
Joined: May 2007
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The first way you described is what I would generally use, but it's definitely a 2 person job. Usually ends up being the quickest and best way to do it.
Last time I did my F100 I used a pressure bleeder system ( got it from Summit) and it worked very well. The master cylinder and proportioning valve were installed completely dry (no bench bleeding) and the lines between the master cyl and prop valve were brand new and completely dry also. Bled fine, works perfectly.
I would avoid using just gravity as I think air bubbles can stay in the system and fluid may still drain past them. Maybe it does work OK, personally I have never tried it.
Some people swear by bench bleeding the master cylinder. I have never done it on any road car or race car I have owned and all of my vehicles have perfect brakes.
If you can't get a good bleed then there's usually still something wrong with a component in the system somewhere.
Last time I did my F100 I used a pressure bleeder system ( got it from Summit) and it worked very well. The master cylinder and proportioning valve were installed completely dry (no bench bleeding) and the lines between the master cyl and prop valve were brand new and completely dry also. Bled fine, works perfectly.
I would avoid using just gravity as I think air bubbles can stay in the system and fluid may still drain past them. Maybe it does work OK, personally I have never tried it.
Some people swear by bench bleeding the master cylinder. I have never done it on any road car or race car I have owned and all of my vehicles have perfect brakes.
If you can't get a good bleed then there's usually still something wrong with a component in the system somewhere.
FTE Legend
Joined: May 2008
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From: In my own world
gravity bleeding not really going to work out for you. proportion valve won't center, and calipers for disc brakes will keep an air pocket. best thing to do is place master cyl in a vice, put some plugs in the place where the brake lines hook up, put brake fluid in the resivor, then take a punch, or screwdriver, and start pushing in where the brake pedal rod goes. keep pushing until all the air bubbles come up , and you can't push in any more. might take as much as 10 min. your arms will definately get tired before this is done. instal the master cyl on the truck, then bleed as you did before. start with furtherest line. have some one pump up the pedal, hold it while you open the bleeder, and push the pedal to the floor, hold it there until you close the bleeder. repeat this until no air comes out, just fluid. check level of breke fluid at master cyl frequently, or you will introduce air back into the system. repet this on all wheels, and you have bleed the brakes. good luck, and let us know how you make out
Elder User
Joined: Apr 2009
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the master cylinder should be bench bled before you install it in the truck, the directions that come with cover that procedure.
the absolute best bleeding that i did to my truck was with a power bleeder, which is basically a 2gallon container of clean brake fluid that is pressurized to 35psi with a seal that goes over the master cylinder. open the valve on the tank, goto the furthest bleeder screw and open it about 1/2 turn, leave it open till clear fluid comes out. then move to next, repeat. it clears all the old fluid out, pushed a bunch of rust and nasty crap out of the brake cylinders and calipers, brakes have never felt better.
the absolute best bleeding that i did to my truck was with a power bleeder, which is basically a 2gallon container of clean brake fluid that is pressurized to 35psi with a seal that goes over the master cylinder. open the valve on the tank, goto the furthest bleeder screw and open it about 1/2 turn, leave it open till clear fluid comes out. then move to next, repeat. it clears all the old fluid out, pushed a bunch of rust and nasty crap out of the brake cylinders and calipers, brakes have never felt better.
Methanoholic
Joined: Mar 2009
Posts: 6,442
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From: Maine (NorCal Native)
I made a vacuum bleeder out of a refrigerator pump, a jar with lid, some silicone hose.
Same pump I used to use to evacuate R12 A/C systems.
I've also created a pressure bleeder as well just by making a plate with and air chuck fitting, rubber inner tube glued to it, cut a notch in the rubber to allow air to both side of the M/C and a c-clamp.
Slowly apply regulated air pressure to ~10-20 lbs. (~10-20 lbs =Approx. 10-20 lbs)
Both work great, I think the vacuum method is not usable on newer brake systems though.
Though I must admit If my son is around we just do it the old fashion way...
Slowly Pump and Hold, (Holding), open bleeder, (Down), close bleeder, Slowly Pump and Hold, (Holding)... ... Assistants actions are enclosed in "()"
-Enjoy
fh : )_~
Same pump I used to use to evacuate R12 A/C systems.
I've also created a pressure bleeder as well just by making a plate with and air chuck fitting, rubber inner tube glued to it, cut a notch in the rubber to allow air to both side of the M/C and a c-clamp.
Slowly apply regulated air pressure to ~10-20 lbs. (~10-20 lbs =Approx. 10-20 lbs)
Both work great, I think the vacuum method is not usable on newer brake systems though.
Though I must admit If my son is around we just do it the old fashion way...
Slowly Pump and Hold, (Holding), open bleeder, (Down), close bleeder, Slowly Pump and Hold, (Holding)... ... Assistants actions are enclosed in "()"
-Enjoy
fh : )_~
Thread Starter
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More Turbo
Joined: Sep 2008
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From: Pennsylvania
Thanks for the advice, everyone. I'll probably avoid gravity bleeding, although, could anyone still give me a run-through of the procedure? It may be handy to know if I'm ever alone and in desperate need of any sort of brake bleeding, or some other extreme situation.
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Joined: Jan 2001
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From: Virginia
I have used gravity bleeding, though it never really gets all the air out. When I find it useful is when I have replaced a large section of the system and it's dry with no fluid. Instead of getting someone to pump while you work the bleeder about 15 times to try and fill the system, if you just open one of the bleeders and leave it open till the fluid starts dripping out, it usually then only takes once or twice with someone helping you to get the last bit of air out of the system.
So all you do is open a bleeder and leave it open till it drips fluid, while making sure the master cylinder doesn't run out of fluid.
I will repeat, it usually will not give you good brakes, it's just a good way to pre-fill the system before you do bleed them with another person or a fancy vacuum gizmo.
So all you do is open a bleeder and leave it open till it drips fluid, while making sure the master cylinder doesn't run out of fluid.
I will repeat, it usually will not give you good brakes, it's just a good way to pre-fill the system before you do bleed them with another person or a fancy vacuum gizmo.
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