Lotus Evora, Service Notes

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Lotus Service Notes Section JL
JL.1 - GENERAL DESCRIPTION
The braking system of the Lotus Evora comprises a four piston calliper and brake disc at each wheel op-
erated by a tandem master cylinder with dual diaphragm vacuum servo power assistance. The dual hydraulic
circuit is divided front/rear and modulated by a Kelsey-Hayes microprocessor based anti-lock system. A cable
actuated parking brake uses brake shoes operating in drums incorporated into the rear discs.
The brake callipers are supplied by A.P. Racing, and feature lightweight alloy bodies housing four pistons
in opposed pairs. The castings for the front and rear callipers are common, but are machined differently to
accommodate the differing piston diameters. In the front callipers, the leading pistons are 38.2 mm diameter,
and the trailing pistons 41.3 mm. The rear callipers house 38.2 mm leading pistons and 36.0 mm trailing. Each
calliper is marked on its inner, inboard face, alongside the pad aperture, with its designated fitting position;
'RF' representing Right hand Front, with others marked as LF, RR, and LR. Each calliper is secured to its hub
carrier by two bolts disposed in a plane perpendicular to the disc axis, with the front callipers mounted behind
the axle line, and the rear callipers ahead of the axle.
The front cast iron discs are 350 mm diameter, 32 mm thick, with optional cross-drilling to enhance pad
cleaning, and include internal curved vanes to draw cooling air from the centre to the periphery, with the vanes
curving backwards in relation to the normal direction of rotation. The rear cast iron discs include similar features,
but are 332 mm diameter and 26 mm thick, and incorporate integral 185 mm diameter drums for the parking
brake shoes. Each disc is sandwiched between the road wheel and hub, and is retained for convenience by
a single countersunk screw.
The Continental Teves tandem master cylinder incorporates a front section to supply both front brakes,
and a rear section to supply the rear brakes. A translucent fluid reservoir is mounted on a bracket above the
master cylinder, and is divided into front and rear chambers separated by a weir. The two chambers are con-
nected to the front and rear master cylinder sections by flexible hose, with a third hose connecting the rear
brake reservoir chamber to the clutch master cylinder to supply that system’s needs. A fluid level sensor in the
filler cap will light a fascia tell tale lamp if the level becomes dangerously low.
The parking brake ratchet lever is mounted between the seats in a fabricated steel structure which also
houses the gearchange mechanism. The lever activates a primary cable which exits the cabin at the front of
the fuel tank bay, and turns through 90° to connect to a balancing yoke at the front of the engine bay. The yoke
forms the abutment for the primary outer cable, with the inner cable continuing through a slot in the yoke to
link to the RH secondary cable. The opposite end of the yoke connects to the LH secondary cable, with both
secondaries leading to their respective rear wheel parking brake backplates. The interaction of the yoke with
the three separate cables results in an automatically balanced force being applied to each of the secondary
cables.
At the each brake backplate the secondary cable connects to a lever mechanism which provides a bal-
anced expanding force to the lower ends of the parking brake shoes. The upper ends of the shoes pivot against
opposite ends of an adjustable length abutment, with access to the toothed adjuster screw available via a hole
in the brake backplate.
The parking brake should be applied by pulling up the lever with high effort, and engaging the highest
ratchet setting attainable. When parking the car on a slope, the additional precaution should be taken of leav-
ing the transmission in first or reverse gear and steering the wheels towards the kerb.
The braking system is designed to enhance brake performance during high speed driving, with good fade
and pad wear characteristics, with the pads offering a higher friction level when heated to normal working tem-
perature than when cold. Required pedal effort will reduce as cold brakes become heated to normal working
temperature, and the braking efficiency will increase significantly as new discs or pads become ‘bedded in’.
After fitting new brake components, maximum braking efficiency will be achieved if, for the first few hundred
miles, needless heavy braking is avoided, and the brake pads are allowed to ‘bed in’ fully before being used
to their full potential.
A Bosch Antilock Brake System (ABS) is used to optimise brake performance in extreme conditions and
reduce the tendency of any wheel to lock up. Under most conditions, the maximum braking force is provided
by a wheel which is rotating at about 90% of road speed. Apart from the likelihood of increasing the stopping
distance, a locked wheel provides no steering force, such that with both front wheels locked, movement of the
steering wheel has almost no effect on vehicle direction. With the antilock system, even panic braking results
in controlled deceleration and the retention of steering response and is especially advantageous when braking
on slippery road surfaces and in bad driving conditions. The ABS control system is self monitoring and has
the capability of switching itself off if a fault is detected, allowing the base brake system to operate without
anti-lock control.