Bench Bleeding Nessecary?

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Feb 26, 2003
OK, I got the SOA done, and went to hook up my brake lines with the new SS, and I found no fluid in the resevior. After hooking everything up, I bled the brakes like 4 or 5 times trying to get the air out, I used the 2 man method and the one man kits from the auto parts stores, and I can't get anymore air to come out. I have probably flushed 4 quarts of fluid through the system. I know that you are suppossed to keep the Master Cylinder full while bleeding, but I think that it may need to be bench bled (The M/C) How do you do this? This is a 78 that has all stock brake system, minus the Bling-bling SS lines from Earls.

Re:Bench Bleeding Necessary?

Bench bleeding is usually done only on new master cylinders, but if you emptied it you may have to do so.

To bench bleed, take the master cylinder off the rig and place in a vise clamping on the mounting flange. You need to get or make lines to go from the brake line outputs and blend them back into the reservoirs so the line will be under fluid level. Fill the reservoirs with fresh brake fluid. Then take a screw driver or punch and push the the cylinder cup in slowly and out slowly. Do this several times and you can watch the bubbles flow out of the lines. Once all the air is out, take the master cylinder back out to the rig, remove the bleed lines, and hook up the regular brake lines. Then have a buddy help bleed the lines at the master cylinder.

What are the symptoms? When I used to work at a shop turning wrenches, we replaced hundreds of masters and never bench bled any of them because it takes more time and you have a greater chance of getting brake fluid on the finish. Because of this experience, I got the impression it isn't necessary.
you can bench bleed it on the truck. get your mate in the cab, remove both brake lines from the master, block the holes with your fingers, fill the master (have a tub on hand to stop fluid on the duco). get your buddy to slowly depress the brake, and let the fuid/ air escape (stop blocking the holes with your fingers) when it reaches bottom of travel, block the holes with your fingers, then tell him to release the pedal, repeat a few times till you have steady fluid flow from both holes when he pushes down. screw back in the hoses, get ready to bleed all 4 wheels (which is how i love spending my sundays :( )

I agree that you can bleed the master cylider on the truck ... The easiest, and most reliable, method that I have found is to attach a short pieces of brake hose with some flexable hose attacked to each. Run the flex hose into each reservoir from each short piece of brake hose. The flex line needs to be below the fluid level in each reservoir .... Then, simply press the brake pedal which cycles the fluid and air through the lines and into the reservoir. The air bubbles out of the fluid in the reservoirs. You can easily do this bench bleed yourself

Good luck
Bench bleeding is called bench bleeding because it is done on the bench. The reason it is done on the bench is because the brake pedal usually isn't capable of bottoming the piston in the bore. Without bottoming the piston there is no guarantee that all air is removed.
If you don't bench bleed the master at first, you will not get all the air out. Been there done that.

you can bottom the piston on the bore in the truck if you adjust the adjustment rod on the pedal almost all the way out. been there done that too:)

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