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On my '68 with power front disc brakes, I have the original style master cylinder with the two bleeder screws on the side of it......It's a new system front to back with either new or rebuilt components including new lines and is completely dry.

So now it's time to fill and bleed the system and the first thing will be to bench bleed the master cylinder and I have the following questions:

1) Can you bench bleed the MC using just the bleeder screws on the side of it or do you bleed it from both the bleeder screws and at the brake line ports also?

2) Should the MC be removed from the car and set level to bleed it or can it be bled in the car in it's natural pointed upwards position? It's in the car now but I'll remove it if I need to.

Thanks......Dave

ps.....can someone tell me about how much brake fluid it should take for the process. I don't want to run out before I'm finished.
 

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Al - Waterloo, Iowa
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Dave, I have never used the MC bleeders. Absolutely remove the MC and bleed
it by holding it fairly level in a vise. I always use tubes from the ports feeding
into the reservoirs. This method keeps any potential spill/mess away from the
car. I just finished the same total process on my car and it took all of 1 qt. Won't
hurt to have an extra qt. When the MC is completely free of air you won't be able
to move the piston much if at all. I believe the manufacturers says 1/8" movement.
It will give your arm a pretty good work out. :wink2:
 

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I just bench bleed my new MC. It can't be installed because you need to push in the cylinder from behind.....I suppose you could do it installed and have someone gently pump pedal....but the term "bench" bleed means do it before installing. I put mine in a vice, level.

Mine did not have bleed screws but did come with bleeding instructions. Yours should have also.

Basically you fill the 2 reservoirs and let the fluid gravity bleed out the ports. Then plug those ports (mine came with plastic threaded plugs). Then you gently push in the cyl as far as you can using a plunger tool. I used a old push rod and a rag wrapped around the end to push on it. Use gentle slow strokes and re-fill reservoirs as needed. It does not take much fluid at all. When no more bubbles come out and you can no longer depress plunger more than a 1/8" (read barley be able to move it at all and the cylinder is now rock solid)

If your MC has bleed screws than use them like you would bleeding brakes. Just run short plastic tube back up into the reservoirs (submerged in brake fluid) and when no more bubbles come out you should have a rock hard MC cyl.

IDK about 68 but my 67 has the FL brake line coming out of the distribution block that has 2 circle bends in it right as it comes out of the block. All other lines just come out. Anyway I found the FL line was very stubborn to bleed. Gravity bleed would not work on that wheel as there was a air bubble that was just stuck in the double loop part of the line which was higher than the exit port of the distribution block. Helper pumping pedal also did not work. Finally used my MightyVac and out came that bubble. YMMV
 

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They make little plastic fittings that screw into the master cylinder where the brake line fits. The other end has a barbed end that mates to a plastic tube.

I clamp the master cylinder in a vice and loop the two plastic tubes back into the reservoir. I push on the piston with a wooden dowel. Most people use a screw driver but the metal might scratch the plunger piston head. Just keep pumping until no more bubbles appear in the hoses. Put the lid on the reservoir and turn the master cylinder sideways a plug the holes where the brake line fits. Mount the cylinder on the car.

It is best to bench bleed a master cylinder off of the car because it can get messy. The brake fluid will eat the paint off of your car.
 

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Discussion Starter #6
Thanks for the bench bleeding tips and the link to the CRG tech. article on the subject.

I've followed the advice and have removed the MC to bleed it outside of the car.....and to bleed it from the brake line ports as opposed to the two bleeder screws on the side of the MC.

One last question on the subject though.....With the two bleeder screws on the side of the MC being higher and directly above the line ports, wouldn't it stand to reason that there could still be air trapped behind the bleeder screws even when the all air is completely purged from the line ports?

What I'm getting at is should you bleed from the two bleeder screws and well as the line ports?

Thanks.....Dave
 

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Not having a MC with bleed screws but If I did I would gravity bleed the MC (bench) until fluid comes out the ports. Then plug those ports and "bleed" the MC using the bleeders

You can use some Teflon tape on the bleeder screw threads but be careful not to block the orifice in it when wrapping the threads
 

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I have never used the screws. I took w old brake lines off the car, bent them back into the resivor. The plastic tubes don't always stay where you put them. Even with the plastic holder. Defiantly do it in a vice. Much easier. A big Phillip's head screwdriver works great.
 

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Plugged ports is the new and improved way to bleed a master. No need for tubes etc. Just use the plugs as above.

Don
 

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Discussion Starter #10
Plugged ports is the new and improved way to bleed a master. No need for tubes etc. Just use the plugs as above.

Don
No quite sure I'm understanding this. Plug the brake line ports and keep pressing the plunger until no more air bubbles rise up in the reservoir ???
 

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No quite sure I'm understanding this. Plug the brake line ports and keep pressing the plunger until no more air bubbles rise up in the reservoir ???
Keep pressing the plunger until it is rock hard and won’t depress any longer. That means all the air is gone. Short strokes.

Don
 

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No quite sure I'm understanding this. Plug the brake line ports and keep pressing the plunger until no more air bubbles rise up in the reservoir ???
The instructions that came with my MC (did not have any bleed screws) said after gravity bleeding so fluid comes out ports to then plug those and continue to pump MC (using some form of appropriate tool) until no more bubbles come up through the small hole in the front & rear MC reservoir. This should be when the plunger gets rock hard so that you can not depress it any more than 1/8"

It did not involve using plastic tube or anything connected to the exit ports (other than plugging the with the supplied plastic threaded plugs) back into the reservoir
 

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I've used the methods discussed above with good results, but I bought one of the Cardone bleeder syringes shown in the links below and it was just too easy. It only took one injection of the syringe in each port to completely purge all air. Easiest, quickest way ever to bleed a MC. While you absolutely don't need this tool, it was cheap so I thought I'd try it just for fun and was amazed how well it worked.


https://cardone.com/products/brakes/brake-products-new/master-cylinder-bench-bleeder

 
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