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I saw somewhere that a special tool is needed to bleed the distribution block/valve next to the master cylinder. It is a plastic screw where you take out the plastic warning light screw with wire sensor and screw this in. Bleed the brakes, then replace the warning sensor screw. Is this necessary? Are there other brake bleeding techniques like bench bleeding the master cylinder? I don't know what that means either. I have everything apart for rebuild. I was going to put it all back together and do the normal bleed at the wheel cylinders. Thanks.
 

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That tool you ask about is not absolutely necessary. It simply locks the shuttle valve that turns the light On in place. After you have finsihed bleeding the brakes, if the light is On, open a bleeder on the rear brakes and slowly push on the pedal until the light turns Off. If it stays On repeat the process on a front bleeder.

Bench bleeding a MC means putting it in a vise, connecting short hoses from the ports back to the reservoirs, filling it with brake fluid and then manually pushing the piston in and out until there are no more air bubbles circulating through the tubes. I don't bench bleed because it makes a big mess. I simply install the dry MC on the car and then bleed the brakes the old fashioned way. This method sends the air bubbles out the bleeder valves at the wheels.
 

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This worked like a charm for me, it allowed me to do it by myself. I topped off the master and put the cap on and put a couple inches of fluid in the gatorade bottle and pushed the hose so it was submerged in the fluid so as to not suck in any air. Connect the other end of the hose on the bleeder screw, just loosen it a quarter turn. I pumped the brake pedal 5 times then checked and topped off the master. Then pump the pedal 5 times again. After checking my bottle a couple of times I got the idea to set my laptop next to the wheel being bled then used facetime with my phone so I could see the bottle while I pumped the brakes. This worked like a charm, once I got fluid moving in the 1st wheel I moved on to the next and repeated the procedure. When you move to the next wheel verify that the tubing is still submerged in the fluid or you will suck air.

 

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I would recommend it. I got away without using it a few times over the years, But the last time that valve closed to the rear and that is no fun to fix. For the price of the tool it's worth it.
 

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If you have the distribution block without the brake light switch, you can bleed your brakes normally. The switch shuttle piston in the other blocks moves when there is a difference in fluid pressure between the front and rear brakes (like when you have leaking wheel cylinders). If you use a brake bleeder bottle and don't push the pedal too hard during bleeding, the block won't see the pressure change. I've used the home made bleeder bottle for 60+ years on hundreds of different vehicles.
 

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This is the type of brake bleeding tool I've used since 1975. It has never failed to work and it works with one person.
748071
 

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This worked like a charm for me, it allowed me to do it by myself. I topped off the master and put the cap on and put a couple inches of fluid in the gatorade bottle and pushed the hose so it was submerged in the fluid so as to not suck in any air. Connect the other end of the hose on the bleeder screw, just loosen it a quarter turn. I pumped the brake pedal 5 times then checked and topped off the master. Then pump the pedal 5 times again. After checking my bottle a couple of times I got the idea to set my laptop next to the wheel being bled then used facetime with my phone so I could see the bottle while I pumped the brakes. This worked like a charm, once I got fluid moving in the 1st wheel I moved on to the next and repeated the procedure. When you move to the next wheel verify that the tubing is still submerged in the fluid or you will suck air.

You know it's a lot easier to just install speed bleeders :) One way valve inside the bleeder so you crack open the bleeder to bleed, but won't suck air when you release the pedal.
 

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You know it's a lot easier to just install speed bleeders :) One way valve inside the bleeder so you crack open the bleeder to bleed, but won't suck air when you release the pedal.
Josh for sure, only issue I live in an area where almost everything has to be ordered online. Would have taken a week to get them. I could have ordered them at a much earlier part of the project but to be honest I've never heard of them until patrick stapler mentioned them when I was trying to bleed them.
 

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You can try turning the key on which will turn on the brake reservoir warning light on if the little shuttle is not centered. Crack open both lines on the master cylinder and leave a wrench on both of them. Have someone gently push on the brake pedal until the light goes out and then tighten the lines before they release the pedal to prevent air from being drawn back into the master cylinder on the return stroke.

I can't remember one time in 100 that I had to center the shuttle after replacing a master cylinder or bleeding brakes on a vehicle.

To replace master cylinder I remove the old one. Clamp the new one in a vise by one of the mounting ears. Stick a finger over both brake line holes. Stick my largest Phillips screwdriver in the back and push the piston all the way in.. You will feel the air coming out from under your finger. You always keep the holes plugged with your fingers on the pistons return stroke. After a few pumps the fluid will start to squirt out and push your fingers away but you never let loose of the holes. A few more pumps and you feel a nice strong flow of fluid pushing your fingers off the hole with no breaks in the flow (air bubbles). Fill the reservoir back up and stick the cap on. Never let it run out of fluid during the bleeding process, Turn the master cylinder on its side so the fluid does not run out of the holes. Stick it back on the car. Start the brake lines before your tighten the master cylinder nuts. That makes it easier to get the lines in without cross threading them. Then hand tighten them. Tighten the master cylinder nuts. Stick somebody in the front seat and tell them not to touch the pedal until you tell them too. Crack open both lines a 1/4 turn and have them step of the pedal slowly, very slowly. A little air will come out and then straight fluid will be coming out. Tighten lines while the fluid is still flowing out and you are done. If there was nothing wrong with the brakes except the master cylinder was leaking no air will get into the system doing it like this. Always make sure your brake rod is not pushing the piston inside the master cylinder at all unless there is pressure on the pedal. The piston should be back against the snap ring.

Good luck pushing with your finger! It better be a really strong and 6" long finger.
748080




There are several ways to bleed a master cylinder. One way is to install plugs in the brake line holes so nothing can get out. When you step on the pedal the air fill be forced out of the cylinder bore and up through the return ports ion the bottom of the reservoir. You can watch the little bubbles coming out of them until there are no more. Then install the lines. Crack them open and bleed the connections like we did above.
748079

Another way is to take some short steel brake lines and install them on the master cylinder and bend them up into a loop and down into reservoir. Then you can jump away one the brakes until no more air bubbles out into the reservoirs. They sell plastic plugs with slip on rubber hoses that do the same thing but the plastic plugs never make a tight seal on the threads and the hoses pop off if you step too fast on the pedal. Then fluid shoots everywhere. Brake fluid eats paint and eats paint and can damage the paint of your fender if your not careful. Immediately wipe it off of any paint and rinse the area with water.

You just stick it right on the car. Fill the reservoirs and have some pump away on the pedal until you no longer see any more air bubbles. When you buy the master cylinder see if they have steel lines that will fit. Sometimes the factory lines have weird size fittings so you need an adaptor to make your little bleeder lines work. This works really well. The only downside is the cost of making the lines.

748077


They sell these Master cylinder bleeding kits with all the fittings to fit l the different master cylinders. The white plastic clips hold the hose down in the reservoir.

748078





Of all the ways to bleed a master cylinder the finger method was the fastest and the messiest. We had steel benches with a big vise on each one right next to each stall. You took the master cylinder out of the box, clamped in the vise, poured fluid. stuck your fingers over the holes, pushed the piston in about a dozen times and you were done. Maybe two or three minutes for that part of the bleeding process. The brake fluid that squirted all over the stainless tops on the work benches cleaned up them like they were new. It was a win-win-deal.



Anytime you work on the brakes for any reason it's "always" a good idea to change "all the fluid" in the system. if you don't work on you are still suppose o be changing it every two-years but hardly anybody does it.

If your are building a complete brake system then you always bleed the master cylinder first so you are not pumping air down into the lines. It makes it almost impossible to get fluid down to th ewheels if a new master cylinder is not bled first. Then move to the furthest rear wheel from the master cylinder, then the opposite rear wheel. Then the furthest front wheel from the master cylinder then the opposite front wheel.
 

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I have never bench-bled a master cylinder. Sure, it might take a bit more bleeding if you don't. In the end, the system is flushed and less mess is made.
We never bench bled at JBA. Seldom was it done at Global.
We had a vacuum bleeder but I never saw it used.
I've centered more than one pressure diff valve. They are a PITA in my opinion.
I greatly prefer to NOT have to fool with it...... hence I used the tool religiously.
I've been working on brake systems since about 1972/3.

ex-Global West GM
1991-1995

748173
 

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I have this valve switch but its not connected. Does it cause an issue when trying to bleed the brakes or not.
 

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I have this valve switch but its not connected. Does it cause an issue when trying to bleed the brakes or not.
The switch lights a warning light on the dash when a loss of brake pressure causes the piston to move. The switch is normally centered by equal brake pressure in the front and rear circuits. The "switch" has no active function and is only connected to the warning light. But often your first and only warning is the BRAKE light on the dash. I've had the light come on and wondered why because the brakes seem to work normally. It might be intermittent at first. And later the pedal gets spongy when the leak gets worse. So it's a matter of safety to have it functional. I've noticed the light will come on when bleeding the brakes if the ignition switch is in the RUN position or it will be on when first starting the car. Step on the brake pedal and it will (should) go off. Never bleed power brakes with the engine running or it may damage the booster. In fact, never bleed any brakes with the engine running.
 

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We never bench bled at JBA. Seldom was it done at Global.
We had a vacuum bleeder but I never saw it used.
I've centered more than one pressure diff valve. They are a PITA in my opinion.
I greatly prefer to NOT have to fool with it...... hence I used the tool religiously.
I've been working on brake systems since about 1972/3.

ex-Global West GM
1991-1995

View attachment 748173
It seems that if the light was already on this tool would be of no help. Can you use a small screwdriver or pick to manually center the valve? I guess if the valve is "stuck" there might be corrosion or gunk holding it there and the valve needs replacement or rebuilding.
 

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Will fitting a proportioning valve at the rear before the diverting block effect the brake valve warning.
 
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