Brake wheel cylinder size & effects

[Crosley.In.AZ]

IF I am getting too much brake ( Drum rear) action on the rear of the vehicle, would a size change larger or smaller in the diameter of the wheel cyl?


Example would be if I have 15/16 diameter wheel cylinders.... a change to 1 inch would give less brake force or change to 7/8 inch wheel cylinder for less force?

[sirstude]

As far as I understand hydraulics, small to big gives the most force with less movement, so I guess go to the bigger wheel cylinder.

Doug

[tomslik]

7/8 will give you less force and a slightly harder pedal

[C9]

Do you have the original factory brakes installed on both ends of the car?

When I used to run an Olds Rocket powered 50 Ford coupe - which came stock with 10" drum brakes both ends - a common modification was to stick a Spicer rear axle out of a station wagon under it.
Mainly to gain a sturdier rear axle, but if you got one out of an OD equipped wagon you got 4.27 gears.

Since the wagons had 11" drum brakes we soon found an imbalance between front to rear.
Panic stops would have the rear end coming around.

Cured when we installed 11" station wagon front brakes.
A bolt in job.

Fwiw - rear axles used were out of 52 - 54 wagons and front brakes were from 52-53 wagons.

So you could go up in front brake power with a disc setup or larger drum if available.

If the smaller rear wheel cylinder helps, perhaps a larger one in front would finish the job and you'd get balanced braking.

A proportioning valve may help as well.
They seem to do the job on the lightweight cars with front disc and rear drum.

[PeterR]

IF I am getting too much brake ( Drum rear) action on the rear of the vehicle, would a size change larger or smaller in the diameter of the wheel cyl?

Smaller piston diameter = smaller piston area = smaller force

With same diameter drum and same lining material, change in braking due to different cylinder diameter is:-

(NEW DIAM)X(NEW DIAM)
(OLD DIAM)X(OLD DIAM)

this means
if you go from 15/16 to 1, the braking will go up to 1.14 which is 14% more
if you go from 15/16 to 7/8, the braking will go down to .87 which is 13% less

If you know the proportion you want to change by, the formula can be reversed

(New diam) = (old diam) x square root(proportion)

say you want to reduce braking to .75

(new diam) = (15/16) x square root (.75)
= .812
which is very close to 13/16

[Crosley.In.AZ]

THis is on my Dodge.  Sometimes it acts like I have too much brake on the rear .  There are disc in front.

Metric GM calipers on front, 11 rotors.  What ever drum size brake on the rear 8 inch Maverick diff.

The M/C and proportioning valve are from a Mopar Duster application.  The sizes of caliper and drum brakes were darn close from the Duster to what is on the Dodge I figured it would work well.

it does work welll , as I mentioned sometimes it seems the rear would like to come around if you KWIM ?

I do have different tires and wheels on the back for a few months.  I will install the set I usually run on the car and see what happens.