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Master cylinder conversion
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Author:  blown55409 [ Wed Aug 08, 2012 12:10 am ]
Post subject:  Master cylinder conversion

Can I convert my master cylinder from disc drum to disc disc? I once read that there was a pressure valve for the drum brakes in the master cylinder that could be removed. I understand it was to keep a slight pressure (10lbs) to keep the shoes from retracting all the way.
The m/c is just a basic chevy unit sold as a disc drum, 1.25 piston, non power.
I also have a seperate rear adjustable brake bias valve.

Author:  gearhead1011 [ Wed Aug 08, 2012 4:52 pm ]
Post subject:  Re: Master cylinder conversion

blown55409 wrote:
Can I convert my master cylinder from disc drum to disc disc? I once read that there was a pressure valve for the drum brakes in the master cylinder that could be removed. I understand it was to keep a slight pressure (10lbs) to keep the shoes from retracting all the way.
The m/c is just a basic chevy unit sold as a disc drum, 1.25 piston, non power.
I also have a seperate rear adjustable brake bias valve.


What you're referring to is a residual valve and it wasn't to keep the shoes from retracting but it would keep some pressure on the seal in the wheel cylinder to keep it from relaxing and letting air in. Disc brakes shouldn't need it but I have heard of some guys using a real low pressure one on applications where the master cylinder is mounted low to maintain a firm brake pedal. On the factory style master cylinders the residual valve was behind the brass fitting that made the seat inside the outlet port. You should be able to remove that fitting by threading a small sheet metal screw into it then pry it out. If you're careful with it you can reuse the fitting after removing the residual valve which is just a small rubber check valve and spring. I'm not sure if you can buy those separately so if you mess it up you may be out of luck.

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