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rlvirago 02-22-2007 03:51 AM

Disc/Disc vs Disc/Drum master cylinders
What is the difference between disc/disc and disc/drum master cylinders, if any and can a disc/drum cylinder be used on a disc/disc set up?

KULTULZ 02-22-2007 04:32 AM


Originally Posted by rlvirago

What is the difference between disc/disc and disc/drum master cylinders, if any and can a disc/drum cylinder be used on a disc/disc set up?

The disc/disc will have a larger fluid reservoir to initiate rear caliper piston movement. The disc/drum will have a smaller rear system reservoir and most likely will include a 10# residual pressure valve, not needed (or wanted) on four wheel disc.

Not interchangeable.

rlvirago 02-22-2007 02:23 PM

Thanks so much for the information.

farna 02-23-2007 08:43 AM

Not necessarily so! I'm using a disc/drum master cylinder on an all disc setup now. The key here is you need to understand hydraulic brake systems thoroughly before making changes. You need to know that the master cylinder you're using will deliver enough fluid volume to apply the brakes, and how the stroke and bore diameters affect braking power before making changes. I haven't found any problems with stroke and volume, but bore diameter has an effect on pressure. A good reference source is the tech section at There are explanations there on pedal ratio effects and bore size.

The reservoir size is usually larger on disc brakes because as the pad wears the piston doesn't move back as far, causeing the fluid level to gradually get lower. US manufacturers decided to make sure there was enough fluid in the front brake reservoir to last the life of the pads and still stop the car even if you never added fluid. The drum brake (rear) reservoir is small because drum brakes have return springs -- the fluid is always returned to the master cylinder no matter what the wear is on the shoes. I check my brake fluid often, so I never worry about reservoir size. Pad wear is gradual unless something is wrong, so there's no real concern if you check the fluid level 3-4 times a year.

I have to add that my current master cylinder is a newer type (late 90s Ford Ranger) that has a single reservoir for front and rear brakes. Doesn't matter much about pad wear -- the same reservoir is affected by both ends of the car.

rlvirago 02-23-2007 06:19 PM

Thanks. I checked out the web site and got a few measurements and I am going to give them a call next week.

staleg 02-28-2007 01:10 AM

Third gen Camaro's use same M/C on disc/drum cars and disc/disc cars.

They change fluid amount on the different setups with different propotioning valves.

rlvirago 02-28-2007 03:33 AM

Thanks. I contacted MP Brakes and asked them the same question about the setup I had and they told me the same thing, so I'm all set to put things together.

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