Originally Posted by Cab_Burge
Originally Posted by TJP
Originally Posted by Cab_Burge
Smaller is better on drum brake wheel cylinders up
Been there done that, put bigger wheel cylinders 1 1/8 on the back and that car didn't stop worth hoot after that. Put the 15/16 back on it started stopping way better, did not change master cylinders either shruggy confused


From a hydraulic engineering viewpoint that doesn't make sense as the larger bore wheel cylinder will apply more pressure on the linings shruggy beer
Thank about that, how can a bigger volume wheel cylinder put more pressure against the brake shoes if the master cylinder size remains the same when you increase the wheel cylinder size work shruggy
I've swap master cylinders sizes from bigger to smaller and got better stopping with no other changes doing that with discs in the front and drums in the back shruggy scope

in the world of Fluid the following applies, lets just put some numbers out:
The formula for pressure is force divided by the surface area.

If the master cylinder has a 1-inch bore, the piston’s surface area is .78 square inches. If you apply 420 lbs. (70 lbs x 6:1 pedal You divide the output force of 420 lbs. by the surface area of the piston, you would get 538 psi(420 lbs. divided by .78 inches) at the ports of the master cylinder.

If you reduce the surface area of the piston you, will get more pressure.

This is because the surface area is smaller, but the output force from the pedal stays the same. So, If you used a master cylinder with a bore of .75 inches that has a piston that has .44 inches of piston surface area, you would get 955 psi at the ports for the master cylinder (420 lbs. divided by .44 inches).

the pressure produced by the master is multiplied by the surface area of the piston at the shoes or caliper. So a smaller piston will aplly less pressure while a larger one will apply more.
One possibility is that the added pressure from the larger bore W/C was causing the backing plate or drum to flex resulting in a loss of surface area contact. shruggy
Research what i have said via google and you'll find I'm not blowing smoke wink beer

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