<VV> Master Cylinder

[Frank DuVal]

I always bench bleed a master. It is simple. Just did a single using my 
gloved hand to cover the outlet, and screwdriver to press the piston 
while holding it in my hand (no workbench or vise used!).

The purpose of bench bleeding is to remove the air from the master 
cylinder. If you do this, and the entire brake system was full of fluid 
before you removed the master, you can bolt the bled master on, attach 
the output lines (one if single, two if dual cylinder), leave the lines 
just cracked, make sure the cylinder is full, have a helper press the 
pedal to the floor slowly, (did I mention having rags and newspaper to 
catch the fluid that runs out?) and you tighten the lines when the fluid 
flows. Doing it this way usually avoids having to bleed any wheel 
cylinders. Always a good choice in the rusty east! Of course if the 
brake pedal is not firm and high, you may still have to bleed the system 
or other trouble shooting.

To bleed a single master, like was original equipment on your 66, close 
the output port. You can use a gloved (nitrile is my choice now) hand or 
a plug. Or, some replacement cylinders come with a plastic tube that 
screws into the port. Put maybe an inch of fluid in the reservoir and 
push the piston (with screwdriver) all the way down until fluid comes 
out the port. Once fluid comes out of the port (may take a second push) 
close the port (hand or plug). Now short stroke (barely push) the piston 
and watch for bubbles coming out of the small hole in the reservoir. 
Keep short stroking until the bubbles go away and a stream of fluid 
comes out of the small hole. Keep adding fluid to keep at least a 1/2" 
in the reservoir. It will go down as the fluid replaces the air in the 
cylinder.

That's it.

Those who do not wear glasses should be warned to wear safety glasses to 
keep flying fluid out of the  eyes.

Frank DuVal



Rich Purtell wrote:
> I am getting ready to replace the master cylinder on my 66 Corsa. I  heard somewhere that there is a technique called bench bleeding. What are the advantages/disadvantages and how is it done?
> Rich Purtell
> 1966 Corsa Conv.
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