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Discussion Starter · #1 ·
I know there are a lot of posts on this issue but nothing seems to help. I had a manual drum brakes. Pulled the MC off and put a new after market chrome master cylinder power booster on my 69 car and I can not get them to bleed. Tried to bench bleed the master cylinder. Tubed the front port and back port back into the reservoirs. Pushed cylinder in many times and can never get all the air out of the tubing. When you push the cylinder in it pushes air out but when you release it, it sucks it back in over and over. I do have the tubes stuck down the the resrvor level. Put it on the car with the MC open and the bleed tubing hooked up and pumped the brake peddle and never removed all the air. Hooked it up to the brake lines and tried to bleed. Pushed peddle to the floor with the bleed screw open and a little fluid and air came out, maybe a inch in my tubing. Closed bleed and let off of the peddle. Opened the bleed screw again and when you do the little bit of fluid in the tubing goes back up into the break line out of the rubber tubing over and over. I have bleed brakes before and all I did was opened and closed and opened and close. I checked the push rod and it set at the proper length, I even put a spacer between the mc and booster to make shure it was not to long just to try. Same old thing I am starting to think the new master cylinder is bad. Should there be a check valve in there some where to keep the air from returning back in to the master cylinder when you push down and release. Also hooked up everything and pumped the peddle and insted of getting harder it seems to get easier as you pump. Dont know what to try next. How do I get the air out if it sucks it back in every time I let of the brake peddle. Getting worried. Dont know what to try next. Help Smez
 

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Copied and pasted from pro-touring.com. Posted by Paul from Hydratech, who knows a thing or two about brakes.

"My favorite way of bench bleeding any basic type of mc is to clamp one of the mounting ears of the mc firmly in a vise, install port PLUGS into the ports, fill the mc with fluid, then start gently stroking the mc piston in / out about 2-3 inches. Resist the temptation to stroke the piston ALL the way in for a few reasons. Stroke the mc a few times to get the ball rollin', then take a small hammer and tap the mc casting a few times, as this gets the small "champagne" bubbles inside to break free of the casting / internal parts - this seems to help quite a bit on fresh calipers too. Gently stroke the mc as described above, tapping the casting a few times arbitrarily during the process. Watch the ports inside of the reservoirs, as you should be able to see the air pockets / bubbles through the fresh clean fluid. You may find that a few very short strokes done repetitiously will help coax these air bubbles out, usually only requiring a 1/2" to 3/4" of stroke in relatively rapid succession. Keep on working until you no longer see any signs of air bubbles in the small ports at the bottoms of the reservoirs, and the mc piston gets immediately firm when pressed in (as the fluid has no where to go with port PLUGS in place). Once the mc piston cannot be pushed in, you know that you have successfully finished your bench bleed procedure. "
 

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You have covered how to Bleed the Master Cylinder but I have a method for bleeding the lines that do not require pumping and continuously locking the bleeders. As usual jack the car up with the rear slightly higher and start on the front brakes ensuring the Master is topped up with fluid through the procedure. I use a Canister about gallon in size Vacuumed Sealed except for an Air Power Tool nipple placed in one end to which I attach a clear neoprene line that will fit over a bleeder. I start the engine and plug into a vacuum source crating a vacuum in the tank and pinch it off using small vise grips. All you have to do is slip the neoprene line over an open bleeder and release the vise grips letting the vacuum draw fluid from the master. You can easily see when there is no air in the lines. If you want after bleeding all lines in this fashion do the Pump Method to ensure a strong pedal resistance.
 

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Discussion Starter · #4 ·
Z15CAM THANKS. I have a vacum pump and thats what I was laying there thinking about doing all night. I dont have the canister but I guess I can just run a tube from my vacum pump to the bleed nipples and pull vacuum on each one and let the fluid go through the vacum pump? While I am pulling vacuum do I have to pump the brakes or hold the peddle to the floor or anything else? I guess I just leave my MC cover off and add fluid as the level drops?
 

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I let gravity do mine. rear end low, front high, opened up coupling on 2 peice rear line, she started dripping after a few minutes, hooked up, flex hose at axle disconnected, took several hours to start dripping, hooked up. Opened lower bleeders on the wilwood rear calipers, dripping there after a few minutes, closed. opened top bleeders, used miti vac to speed things up. Sucked master dry, starting over...lol.
 
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