Kubota RTV1140CPX, Workshop Manual

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BRAKES
RTV1140CPX, WSM
4-M4
4. MASTER CYLINDER
The master cylinder is intended to convert the brake pedal operating force to the fluid pressure. It is composed of
the reserve tank that contains the brake fluid and the cylinder proper that generates the fluid pressure. There are
several different fluid pressure generating mechanisms. Kubota has picked up the tandem type cylinder out of them.
Even if a pipe has got cracked and the front or rear set of wheels have failed to get braked, this mechanism can apply
the brakes on the other set of wheels.
(This is to comply with the rules and regulations stipulating that two lines must be independently controlled.).
Step on the brake pedal, and the push rod (12) drives the piston (9) the primary cup blocks the relief port
"a" , and
the path between the pressure chamber and reservoir is shut off. As the piston moves on, the brake fluid flows through
the brake hose or pipe to the front wheel brake piston and the rear wheel brake cylinder, and the fluid pressure is then
boosted.
When releasing the brake pedal, and the piston returns to its initial position under the force of the return spring.
But the brake fluid in the front wheel brake piston and the rear wheel brake cylinder is delayed in flowing back, which
puts the pressure chamber under negative pressure.
To get rid of the negative pressure, the brake fluid in the reservoir flows through the supply port "b" , supply
chamber and piston-end small hole "c" , along the back of the primary cup, into the pressure chamber.
Now the brake fluid flows back from the front wheel brake piston and the rear wheel brake cylinder.
The brake fluid in the reservoir fluctuates in volume, but there is no pressure fluctuation thanks to the reservoir
cap that has a small hole open to the atmosphere.
The tandem type master cylinder works like this. Step on the brake pedal, and the push rod (12) activates the
primary piston (8) first (spring force different between front and back; front one weaker), raising its pressure. The
primary piston gets balanced in pressure with the secondary one (9) (fluid pressure adjustment). Now the brakes are
applied.
The relief port "a" (at the secondary piston side) absorbs temperature dependent volumetric changes in the brake
fluid. This helps prevent fluid pressure buildup when unnecessary. If this port is clogged, the braking effect may drag
on. (At the primary piston side, the clearance between the needle (6) and piston, as well as the one between the pin
(7) and master cylinder body (5), serve as the relief port.)
9Y1210293BRM0005US0
(1) Cup
(2) Diaphragm
(3) Filter
(4) Reserve Tank
(5) Master Cylinder Body
(6) Needle
(7) Pin
(8) Primary Piston
(9) Secondary Piston
(10) Internal Circlip
(11) Boot
(12) Push Rod
(13) Yoke
(14) Grommet
a: Relief Port
b: Supply Port
c: Small Hole
KiSC issued 05, 2014 A