I need to replace the rear wheel cylinders on my studebaker. Factory disc brake cars where 3/4" the new replacement are 7/8 same as a drum brake car. Hows this going to affect stopping?
changes in wheel cylinder diameter effect brake bias..
larger wheel cylinders increase the applied pressure to the shoes..
i happen to have an old Safe line brake catalog with pictures of wheel cylinders and if there is more than one size per shape..
what year is your car.. perhaps i can snag some part numbers somewhere to see if there is a cross ... so you can reverse cross it.
if your back brakes lock before the front brakes.. you could go to smaller diameter wheel cylinders..
if your front brakes lock up before the rear you could go to larger wheel cylinders.
this does not involve one of those adjustable pressure devices that limit or reduce the pressure to the rear brakes..
so if you have larger wider tires on the rear .. you may want the larger diameter wheel cylinders on the rear.. same if you went to skinnys up front.. you need more brake bias to the rear.. so you don't lock up the fronts..
i miss working on old silver and golden hawks.. back in the early 80s i had several customers with them. grease fittings everywhere.. one was a supercharged model. he had bought them new.. when one passed.. his kids scrapped the cars.. i cried.. get those old cars out of the driveway his wife told me they demanded.
try a W7568 at rock auto
More Information for DORMAN W7568
Bleeder Screw Cap Included No
Bleeder Screw Included Yes
Bore Size 3/4"
Brake Component Inlet Thread Size 3/8-24 UNF
Material Cast Iron
Use Location Rear
Alternate/OEM Part Number(s): 5473023, 8126797, A6110
Thanks waynep 712 I'll check that out. That's where the brake shoes are coming from and they had the 7/8 cylinders. This is a 64 GT Hawk not super charged. Wish it was. But maybe someday.
One thing to keep in mind. If you were to use the larger wheel cylinder you would have terrible pedal feel. A larger wheel cylinder, like was said above, will apply much more pressure...BUT it will move far far less. That will give you a low, mushy pedal. It may not even move the rear shoes enough to apply them adequately. So I'll parrot the guys above, dont use them...not even if you change both.
this is just a shout out.. actually a scream from a professional mechanic with 35 years of experience.
actually... a 1/8 inch change in wheel cylinder sizing really should not be felt by change in the pedal height..
the IMPORTANT thing.. getting the brake bias correct rather than any pedal feel..
having all 4 wheels lock up at the same time in a panic stop is really the most important thing.
if the rears skid first.. the back end can come around... if the front skid first.. you will have a LONG LONG stopping distance without steering input..
nascar guys have tandem master cylinder with an adjustable fulcrum and a giant knob on the dash board so the driver can change the brake bias before trying to slow down to come into the pits to match the much lighter rear end of the car.. but they are slowing down from 190 miles an hour to 55 and then to zero and need to stop within just a few feet ..
the best we can do is get our cars with a decent brake bias... in the 60s it was easy with drum brakes all the way around.. vary the wheel cylinder sizes with front disc brakes... you are limited to the size of the rear shoes and the rear wheel cylinders ..
i also dislike using wheel cylinder kits on wheel cylinders that don't have a perfect bore.. it take the wheel cylinder off... wash it in brake fluid.. not solvents.. wire brush it in brake fluid.. run a fine grit wheel cylinder hone all the way thru using brake fluid.. wash again. inspect the bore.. if there are no corroded spots.. then rebuild... if you cannot find replacements.. there are several brake specialists who can bore and sleeve them in stainless or brass.. why not wash them in solvents. because any solvent used including water base solvents will get into the cast iron . it may soften and cause distortion of the rubber cups eventually... baking the wheel cylinders. may work to eliminate any trapped solvents.
end of shout.. not the end of my shouting to do it right .. don't do it half way.. it takes significant amount of time to build our hotrods and muscle cars.. crying over a 25 or even 50 buck each pair of wheel cylinders is crazy.. they are far cheaper than even the primer used on the front fenders that may become damaged when the brakes don't work perfect..
Way nep thought you may like to see what I'am working on. This is not my car as mine is in the middle of a frame off restoration but this is a twin to what I have,
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