Thank's for the replies guys. I already assembled the rear end with the 15/16" cylinders but it will be a while before I can install the axle asmy in the car. I'll try it out this way to begin with and see what happens.  Dave

SE Wis

The Center of Gravity (CG)  location is a major factor in determining the ratio of the front verses the rear bore diameters of the wheel cylinders (WC's).  Under hard braking, the acceleration force acting through the CG causes more downward force on the front tires and less force on the rear tires.  If the front and rear WC's had the same bore diameters, the rear wheels would lock up (skid) first -  likely causing the rear end of the car to swing around. Obviously this is not good, which is why the rear WC's have smaller bores than the front WC's which provide more braking to the front wheels and less to the rear wheels.  The 1957 Ranchero (and later) probably had a lower CG than the 1956 Victoria, which would cause less loss of rear tire vertical force during hard braking - hence a larger rear WC bore than the Victoria.  15/16" diameter verses 7/8" diameter doesn't sound like much difference, but it's the bore area times the pressure that produces the shoe force from the WC.  The bore area is related to the diameter squared. It is calculated as [(Dia)^2 x (3.1416)]/4 .  So if you do that calculation for both WC's ,  you will see that the larger 15/16"  WC produces almost 15% more force.  Like fatphil1 says, this would probably only be an issue during hard braking on wet pavement.  However,  if it were me, I think I would play it safe and have the Ranchero Rear WC's bored and sleeved  to 7/8" diameter. 

It will make a SLIGHT difference. The basic leverage idea is "the bigger the swept area (Wheel cylinder bore size) the more pressure output on the shoes creating more clamping force. But remember that "everything is give and take" in that you'll have more pedal travel to move the WC piston the same distance along with (a slight possibility) excess pressure causing wheel lock up, probably only on wet roads.  

Your real world answer is "try it!" as other guys with heavy chassis cars have ADJUSTED bore sizes up 1/16" or so for years like my 1ton wheel cyls on my C20 scruby. Chrysler cars always had twitchy/grabby brakes and I FIXED them by downsizing the rears slightly (Prob an engineering error).

One thing: shoe adjustment is CRITICAL on a oversized system. I'd suspect  your backing plates have adjuster holes for brake spoons. if they don't, CREATE THEM and make your life easier. You'll have a better pedal keeping the shoes adjusted. That was a mistake I made initially and had to tear down my full floating axles to do the adjustments (I hate rechecks!)           

Thanks for that info Jim. I guess I'll go that route.  Dave

SE Wis

I'm using a 67 Mustang  dual master on my  57 Ranchero with the 15/16 rear wheel cylinders with no problems..

The Mustang MC is the same bore as the Victoria being 1". I was just wondering if changing the rear cylinder size would affect things.  Dave

SE Wis

I'm installing a 9" rear end from a 58 ranchero in to my 56 Victoria. The wheel cylinders in the 9" are 15/16" bore, the 56 has 7/8" bore cylinders. Which cylinders should I be using for proper braking to work  with the master cylinder and original front brakes? I do have a dual MC from a 67 Mustang which has worked well for years.  Dave

SE Wis