The master cylinder for a drum brake system generally uses the same volume for both front and rear brakes; a disc brake uses a higher volume hence the different size reservoirs. A disc frt/drum rear system uses a metering (frt. hold off) valve usually holds off pressure to about 110 psi as the disc brake applies quickly and drums slower at start of stop. All drums don't use this valve. A disc/drum or a disc/disc usually has a valve in the rear system called a proportioner to slow down the pressure rise to the rears (prevents early rear skids from weight balance (light rear) and/or drum self- engergization). Master cylinders should match the volume of the wheel cylinders.
Last edited by 35 trucker; 12/15/2007 6:47 PM.
