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Lotus Evora. Manual - part 48

Lotus Service Notes

Section JL

2. Remove the two bolts securing the brake calliper to the hub carrier, and withdraw the calliper from the

disc. Secure clear without straining the flexible hose.

3. Remove the single countersunk screw, and withdraw the disc from the hub.

4. Before re-fitting a disc, ensure that the mating face between disc and hub is scrupulously clean. Mount

the correctly handed disc (with the curved vanes trailing in normal direction of rotation) onto the hub spigot,

align the fixing screw hole, and secure the disc with the screw, tightening to 10 Nm.

5. Apply Permabond A130 (Blue - A912E7033) to the threads of the calliper fixing bolts. Fit the calliper with

pads over the disc and secure to the hub carrier with the two bolts. Tighten to 86 Nm.

6. Refit the road wheel and when all brakes are assembled, pump the brake pedal to restore brake pad posi-

tion before driving the car.

Rear Disc Replacement

Replacement of the rear discs is similar to that for the front discs, except that the adjuster for the parking

brake shoes should first be slackened to allow easy withdrawal of the disc/drum. Re-adjust after re-assem-

bly.

JL.7 - BRAKE CALLIPERS

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 38.1 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 brake callipers are to be dismantled or overhauled only A.P. Racing at Wheeler Road, Seven Stars

Industrial Estate, Coventry, CV3 4LB.

Front calliper fixing bolt torque; 86 Nm using Permabond A130.

Banjo bolt, flexi hose to calliper; 20 Nm.

Flexi hose to subframe bracket; 16 Nm.

JL.8 - BRAKE MASTER CYLINDER

The Continental Teves tandem master cylinder incorporates a rear section to supply both front brakes,

and a front 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 master cylinder is secured to the front face of the brake servo which itself is bolted to the front of the

pedal box. Access is available only after removal of the front clamshell. The master cylinder manufacturer

does not recommend any dismantling of the unit, and supplies no replacement parts or internal components.

If the cylinder is faulty it should be renewed as a complete assembly.

To remove the unit, proceed as follows:

1. Remove the front clamshell (see Sub-section BV.4) and radiator air outlet duct.

2. Syphon fluid from the reservoir to reduce spillage. Release the two hoses connecting the master cylinder

to the fluid reservoir, and plug the hoses. Disconnect the electrical cables from the reservoir cap.

3. Release the two brake pipes from the master cylinder, and plug the pipes and ports.

Lotus Service Notes

Section JL

4. Release the two nuts securing the master cylinder to the brake servo and remove the cylinder.

5. Refit the master cylinder in reverse order to removal, using new locknuts and tightening to the following

torques:

- Master cylinder fixing nuts; 25 Nm

- Brake pipes to cylinder; 16 Nm

6. Fill the reservoir with DOT 4 non-mineral type brake fluid, and bleed the complete brake system of air

using the procedure in Sub-section JL.3.

JL.9 - VACUUM SERVO UNIT

The vacuum brake servo is secured to the front face of the pedal box via a machined alloy spacer, and is

operationally interposed between the brake pedal and master cylinder. Engine generated vacuum is used to

provide pneumatic assistance to the effort applied at the pedal. The unit is supplied by Continental Teves and

is a dual diaphragm unit combining a 178mm (7 in) and 203mm (8 in) diameter vacuum chamber into a single

compact unit to provide a 5:1 assistance ratio. With the exception of the air filter and vacuum elbow/non return

valve, the unit is a non-servicable sealed unit which if found to be faulty, must be replaced as an assembly.

The air filter (surrounds the input push rod) should be replaced whenever the brake system is overhauled, and

cleaned or replaced more frequently if the vehicle is operated in dusty conditions. A non-return valve is incor-

porated into the vacuum hose elbow connector in the front case of the servo unit. The elbow connector valve

is a push fit into a grommet in the servo shell, and is supplied complete with the grommet.

The servo is of the ‘suspended in vacuum’ type, wherein two flexible diaphragms divide each of two sec-

tions within the steel shell into two chambers. One pair of chambers, towards the front side of each diaphragm,

is connected via a non-return valve, to the vacuum produced in the engine’s inlet plenum chamber. The second

pair of chambers, towards the rear side of each diaphragm, connect either to the front chambers, or to atmos-

phere, under the control of a double acting face valve.

Brakes Off

When the brake pedal is released, the diaphragms and driving piston are pushed fully rearwards by the

main spring, and the input rod (connected to the brake pedal) is also pushed rearwards by its own spring, caus-

ing the face valve to close the atmospheric connection. Engine vacuum admitted to front of the diaphragms is

also communicated to rear of the diaphragms via the face valve. The unit is in stable equilibrium.

Initial Movement

Initial movement of the brake pedal causes the input rod, input piston and face valve to move forwards,

closing off the front/rear communication.

Pressure Balance

Further pressure on the brake pedal pushes the input piston further forwards and opens the face valve to

bleed atmospheric pressure into the rear chambers. The resultant pressure imbalance across the diaphragms

acts to apply a force to the driving piston to assist pedal effort. When the combined input force from foot pressure

and servo pneaumatic pressure balances the reaction force of the main spring and master cylinder, movement

of the driving piston ceases, and both face valve ports close. The system is once again in equilibrium.

Lotus Service Notes

Section JL

From this position of equilibrium, further pressure on the pedal will tend to open the atmospheric valve

face and allow pressure in the rearward chambers to increase, and move the driving piston forwards before

again stabilising. Any reduction in pedal pressure will tend to open the front/rear valve face and allow the higher

pressure in the rearward chambers to bleed off into the frontal chambers, whose depression is kept low by

connection to the intake plenum. The pressure imbalance allows the driving piston to move rearwards under

the action of the main spring and master cylinder, until equilibrium is regained.

Maximum Assistance

At around 900N of input rod pressure, the atmospheric port will be held open, so that the rearward cham-

bers will be subject to full atmospheric pressure. This constitutes maximum servo assistance which will, with

0.8 bar of vacuum available from the engine, increase the force applied to the master cylinder pushrod by a

factor of five.

The pliant reaction disc fitted between the input and output rods ensures a graduated application of servo

assistance and provides pedal feedback and ‘feel’ to the driver.

Operational Check

As a quick check of servo operation proceed as follows: With the engine stopped, press the brake pedal

several times to exhaust the servo unit of vacuum. Keeping the pedal pressed (which should be ‘hard’ and

‘high’), start the engine; The pedal should drop slightly as the servo vacuum builds up, and extra force is pro-

duced. If the pedal does not drop, it is most likely that there is a fault in the vacuum supply line. Check the

vacuum hose, all connections and the non-return valve. If the vacuum supply is not defective, the servo unit

should be replaced.

Tandem Servo Section (brakes off)

Vacuum supply

Atmospheric Driving piston

chambers

Pliant reaction disc

Atmospheric Communication

Atmospheric

valve face

Input

rod

Air filter

Front/rear

communication

Input piston

Main spring

Vacuum communication

j194

Vacuum chambers

Atmospheric communication

Lotus Service Notes

Section JL

Setting brake pedal: It is essential that the servo piston (and master cylinder piston) is allowed to return fully

when the brakes are released, and is not pre-loaded by mal-adjustment of the input pushrod. See (4) below.

Stop light switch: The stop switch is mounted in a right angle bracket fixed to the underside of the scuttle, and

abuts directly against the pedal. The switch is retained in the bracket by a quarter turn mechanism, with no

adjustment provided or required.

To Replace Brake Servo Unit

1. Remove the brake master cylinder (see sub-section JL.7).

2. From within the footwell, disconnect the servo pushrod from the brake pedal.

3. Disconnect the brake servo vacuum hose, and release the four nuts securing the servo to the pedal box

extension plinth. Withdraw the servo assembly.

4. Before replacing a servo unit, first check the adjustment of the clevis on the input pushrod (i.e. the effective

length of the pushrod). With a new rubber gasket fitted over the four servo mounting studs, the perpen-

dicular distance from the surface of the gasket to the axis of the clevis pin hole should be 133mm.

5. Replace the servo in reverse order to the above, tightening the servo mounting nuts to 25 Nm, and the

master cylinder new fixing nuts to 25 Nm. Check pushrod adjustment (see sub-section JL.9) and bleed

the hydraulic system (see sub-section JL.3)

JL.10 - PEDAL BOX

The pedal box is fabricated from alloy sheet, and rivetted, bolted and bonded to an aperture in the chassis

scuttle. A hollow steel pivot shaft serving the brake and clutch pedals is bolted to a steel mounting plate, itself

bolted to the inside of the pedal box. The brake and clutch pedals are fabricated from steel plate, and feature

synthetic bushes for maintenance free articulation on the steel pivot shaft, and serrated alloy footpads. The

brake pedal uses a coil pull off spring, and the clutch pedal is equipped with an overcentring coil spring linkage,

in order to reduce the pedal effort required to maintain full clutch disengagement. A clutch pedal potentiometer

is also fitted in order to provide data for Cruise Control operation, and for the start inhibit function on Canadian

market cars.

The 'drive by wire' throttle actuation uses a steel rod fabricated pedal to operate an electronic module and

provide a signal to the engine ECU, which then actuates the throttle valve stepper motor within programming

constraints. The throttle pedal module is secured to a mounting bracket by three bolts, with a further three bolts

fixing the bracket to the pedal box.

Pedal Removal

To remove the throttle pedal assembly complete with mounting bracket, disconnect the harness plug from

the module, and remove the three bolts securing the bracket to the pedal box.

To remove a brake or clutch pedal from the pivot shaft, the pedal shaft mounting plate must be removed

from the pedal box complete with the brake and clutch pedals:

1. Unplug and remove the throttle pedal assembly complete with mounting bracket by releasing the three

screws securing the bracket to the pedal box.

2. Disconnect the brake and clutch pedals from their pushrods, and unhook the brake pedal return spring.

3. Unplug and remove the clutch pedal position switch with mounting bracket, by releasing the two bolts

securing the bracket to the pedal box.

4. Release the clutch pedal assistor spring anchor bracket from the pedal box side (3 bolts).

5. Remove the two bolts securing the clutch master cylinder assembly to the pedal box and support the

cylinder aside.

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