Brake master Cyls

[sandy wilson]

Although I have not converted to either the front 80mm, or rear disc
brakes it is on my wish list.
One way of determining the master cyl size is working out the volumes
required. I have read a recent past message that touched on this very
subject. For those that have converted, or have the parts on hand,
please measure the dia of the caliper piston. Asssuming the travel will
be small as disc pads run at near zero clearance (perfect world), we
should be able to determine the total displacement required for the
master cyl for various applications. These could be various combinations
of... front 80mm/std rear conversion. Front 80mm/ 1 1/16 rear wheel
cyl.or full 6 wheel disc's, etc, etc.
I think there are enough on this net with the mechanical/technical
skills to put this to rest. After the numbers have been crunched it is
only a matter of finding a master cyl with the physical dimensions to
fit our application. This is just the typical leg work that a company
like Caspro does and charges an upcharge for.
Just a thought.
Regards, Gil

 

[blank]

Gil,

The theory is good, but apparently doesn't work out well in practice. In a
perfect world, the 80mm calipers should require only marginally more volume
than the OEMs(don't recall the bore diameter on those) and the rear calipers
should actually require less volume than the OEM wheel cylinders. It just
doesn't work out that way in the real world. Apparently there are several
factors that cause the caliper pistons to have a greater range of motion.
These could include variations in rotor thickness, rotor slightly out of
true, flex of the caliper mount, flex of the caliper itself and vibration
from suspension motion. I'm sure there are more, but with the trouble many
GMCnetters have run into with OEM type master cylinder when upgrading the
brakes, it's obvious that these factors are at work. If the larger P-30
master cylinder becomes the obvious fix, then this is one time to "toss" the
theory for something that actually works.

Patrick

>
> One way of determining the master cyl size is working out the volumes
> required. I have read a recent past message that touched on this very
> subject. For those that have converted, or have the parts on hand,
> please measure the dia of the caliper piston. Asssuming the
> travel will
> be small as disc pads run at near zero clearance (perfect world), we
> should be able to determine the total displacement required for the
> master cyl for various applications. These could be various
> combinations
> of... front 80mm/std rear conversion. Front 80mm/ 1 1/16 rear wheel
> cyl.or full 6 wheel disc's, etc, etc.