Issues Bleeding Stock Brakes
Drifting
Joined: Jan 2012
Posts: 1,908
Likes: 129
From: Fredericksburg Virginia
I'll second that emotion. As a pre-curser to the "real" bleed, I will either use the pedal pusher, or the vacuum widget to get some "scouring velocity" through the line. Only after the fluid runs golden clear will I then deploy a gravity bleed.
Melting Slicks
Joined: Jun 2011
Posts: 3,116
Likes: 598
Gravity Bleeding usually works well if the air is in the caliper where the air bubble can rise up to the bleeder screw.
Air rises, fluid (gravity force) pulls fluid down. So it depends on where the air is trapped.
air usually get trapped in a few places.
1. behind the caliper pistons.
2. in the hose
3. proportioning valve
4. Master cylinder
5. in the line where it changes direction. (up down)
To move the air you need enough force to over come the fluid viscosity. So depending on the fluid and temperature of fluid size of the bubble it might and might not be removed with gravity bleed only. Therefore you add the pedal pushing with a open bleeder. This usually requires 2 people.
Like myself and many others the count is 1 person. So that is where the other options come in.
To bleed effectively you need to know where is in the system. (based on what part of the system was opened.
1. Start at the master cylinder (always) (bench bleed as best you can) then use this method to get the last of the air while on the car.
https://www.corvetteforum.com/forums...-cylinder.html
Once this is done using a pressure method or pedal pushing method you wont be pushing air into other parts of the system.
The order you bleed "my opinion" doesn't matter except for the amount of fluid you use. So to reduce the amount of fluid required. Start with the longest path brake circuit.
If the system wasn't open then gravity bleed (if you want to wait or have time to burn) to replace the fluid. If you opened the brake system then the fastest and best way is to apply pressure at the master cylinder (don't care what method you use) can be a motive device or pedal pushing etc but use pressure. Those that use vacuum at the bleeder have the problem "to see" when the air is gone. This is because the air pressure difference at the connector and the vacuum system can exceed the hose to bleeder seal and pull air, making you think you still have air in the system. (leads to excessive fluid use).
The more pressure you can apply the more effective you will be in removing air in the hard to get places. "this is usually required with a completely opened system."
If you are only replacing fluid all the methods mentioned will work.
I bleed my brakes before every track day, usually ever 2 weeks so being efficient is important to me.
Air rises, fluid (gravity force) pulls fluid down. So it depends on where the air is trapped.
air usually get trapped in a few places.
1. behind the caliper pistons.
2. in the hose
3. proportioning valve
4. Master cylinder
5. in the line where it changes direction. (up down)
To move the air you need enough force to over come the fluid viscosity. So depending on the fluid and temperature of fluid size of the bubble it might and might not be removed with gravity bleed only. Therefore you add the pedal pushing with a open bleeder. This usually requires 2 people.
Like myself and many others the count is 1 person. So that is where the other options come in.
To bleed effectively you need to know where is in the system. (based on what part of the system was opened.
1. Start at the master cylinder (always) (bench bleed as best you can) then use this method to get the last of the air while on the car.
https://www.corvetteforum.com/forums...-cylinder.html
Once this is done using a pressure method or pedal pushing method you wont be pushing air into other parts of the system.
The order you bleed "my opinion" doesn't matter except for the amount of fluid you use. So to reduce the amount of fluid required. Start with the longest path brake circuit.
If the system wasn't open then gravity bleed (if you want to wait or have time to burn) to replace the fluid. If you opened the brake system then the fastest and best way is to apply pressure at the master cylinder (don't care what method you use) can be a motive device or pedal pushing etc but use pressure. Those that use vacuum at the bleeder have the problem "to see" when the air is gone. This is because the air pressure difference at the connector and the vacuum system can exceed the hose to bleeder seal and pull air, making you think you still have air in the system. (leads to excessive fluid use).
The more pressure you can apply the more effective you will be in removing air in the hard to get places. "this is usually required with a completely opened system."
If you are only replacing fluid all the methods mentioned will work.
I bleed my brakes before every track day, usually ever 2 weeks so being efficient is important to me.
Burning Brakes
Joined: Oct 2003
Posts: 1,090
Likes: 74
From: New Carlisle IN
When i was living with my parents, we only used the two person method with the brake pedal. Now that i live alone, it's sometimes hard for me to get someone over to help me out, especially when i need it done in order to go race the next day. So I bought one of the motive power bleeders. It works great. Keep pressure and fluid in the system and all you have to do is move to each caliper, open the bleeder and let the fluid/air drain out. Very simple and easy for one person to do.
Gravity bleeding usually takes too long for me. I am usually buttoning up a job the day before i need to go to an autocross somewhere. I have done it before, and it does work, just not quickly.
BTW, my dad was a brake tech for BOSCH at their proving grounds. Power bleeding is how they did most of their hydraulic systems (though the work on air brakes for trucks most of the time). Since he has retired and the proving grounds were sold off, dad was able to acquire a coupe of the pressure bleeding systems that they used there. It is a stainless steel ball that has a bladder inside. Fill the bladder with fluid. There is a schrader valve on the bottom to pump up the air pressure against the bladder. In this system, the air and the pressure are separated from each other. In essences, it operates the same as the motive bleeders. After i moved out, he lost his "helper" for bleeding his own brakes. So he now uses the pressure bleeder also.
Dad has made some adapters to go into he fluid reservoirs on his 90 and my 91. I just used it to bleed the brakes on my 91 after I bought it. There was a very spongy pedal. After the bleed, the pedal was rock solid. I got quite a bit of air out of the rear calipers and a lot of old, dark fluid.
Gravity bleeding usually takes too long for me. I am usually buttoning up a job the day before i need to go to an autocross somewhere. I have done it before, and it does work, just not quickly.
BTW, my dad was a brake tech for BOSCH at their proving grounds. Power bleeding is how they did most of their hydraulic systems (though the work on air brakes for trucks most of the time). Since he has retired and the proving grounds were sold off, dad was able to acquire a coupe of the pressure bleeding systems that they used there. It is a stainless steel ball that has a bladder inside. Fill the bladder with fluid. There is a schrader valve on the bottom to pump up the air pressure against the bladder. In this system, the air and the pressure are separated from each other. In essences, it operates the same as the motive bleeders. After i moved out, he lost his "helper" for bleeding his own brakes. So he now uses the pressure bleeder also.
Dad has made some adapters to go into he fluid reservoirs on his 90 and my 91. I just used it to bleed the brakes on my 91 after I bought it. There was a very spongy pedal. After the bleed, the pedal was rock solid. I got quite a bit of air out of the rear calipers and a lot of old, dark fluid.
Last edited by vettehardt; Feb 21, 2018 at 02:26 PM.
