Lotus Elise / Lotus Exige. Manual - part 55

   Lotus Service Notes

                Section JJ

Page 3

JJ.1 - GENERAL DESCRIPTION

The Lotus Elise, when fitted with anti-lock brakes, comprises ventilated discs all round with AP Racing 2-

piston fixed callipers on the front and Brembo single piston sliding callipers on the rear.  A tandem master
cylinder, with vacuum servo assistance, operates the callipers via a front/rear split hydraulic circuit with anti-
lock control by a Kelsey-Hayes microprocessor based system.  The centrally mounted parking brake lever,
operates the rear calliper pistons by control cables.

The AP Racing front callipers, have lightweight alloy bodies housing two opposed pistons, and are mounted

via two bolts directly to the rear of the forged steel hub carriers.  The rear brakes use Brembo cast iron, single
piston callipers, sliding on pins mounted directly to the forged steel hub carriers.  A ventilated cast iron brake
disc with curved internal vanes and cross drilling is common to all four wheels, and is sandwiched between the
road wheels and hubs, retained for convenience by a single countersunk screw.

The tandem master cylinder is made by FTE, and 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 has separate compartments connected to the front and rear cylinder sections by flexible
hose.  A third hose connects the rear reservoir compartment with 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 and uses a short primary cable and balanc-

ing yoke to actuate a single control cable linked to each rear calliper.  Adjustment of the calliper mechanism to
compensate for brake pad wear is automatic.  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 leaving the transmission in first or reverse gear and steering the wheels towards
the kerb.  If the parking brake is applied when the brakes are hot (e.g. after prolonged or vigorous braking),
special care should be taken to ensure that the parking brake is securely engaged in order to allow for any
potential affect on brake performance as the discs cool.

The braking system is designed to enhance brake performance during high speed driving, with good fade

and pad wear characteristics, and have a higher friction level when heated to normal working temperature 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 Kelsey-Hayes Antilock Brake System (ABS) is used to optimise brake performance in extreme condi-

tions 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, move-
ment of the steering wheel has 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.

Under normal circumstances, the hydraulic power brake system of the vehicle operates without input

from the ABS, with brake pressures governed by the force applied to the brake pedal.  The ABS microprocessor
receives signals from wheel speed sensors at each of the four wheel hubs, and interprets this data to determine
if any wheel is tending to lock up.  If imminent lock up is determined, the microprocessor commands solenoid
valves in an electro-hydraulic unit to reduce the pressure in that particular brake circuit in order to restore wheel
speed to that providing the maximum braking force consistent with continued wheel rotation.

When the ABS is operating, indication to the driver is provided by a 'pulsing' sensation felt at the brake

pedal as fluid is pumped between the master cylinder and hydraulic control unit, and also by audible clicking of
the relays and switches.  These signals indicate to the driver that maximum retardation is being approached,
and that driving style should be modified to suit the conditions.  The minimum stopping distance is achieved by
applying the brakes firmly and steadily, and allowing the ABS to modulate hydraulic pressure.  The driver
should not attempt to emulate this process by ‘pumping’ the brake pedal, as modulation at the pedal will treat
all four wheels similarly, rather than the individual wheel control allowed by the electronics.

During ABS operation, the wheels may appear to lock momentarily as the wheel speed changes rapidly,

and some tyre noise (intermittent screeching) may be heard.  This noise is normal and will vary with road and

 

   Lotus Service Notes                                  Section JJ

Page 4

tyre conditions.  However, a wheel that completely locks and stays locked for more than one or two seconds is
not normal, and indicates that the vehicle should be serviced as soon as possible.  The ABS cannot operate
properly if the base brake system is faulty, and will also be affected by dragging brakes, faulty wheel bearings
or other related faults.

The ABS controller constantly monitors the anti-lock system for faults, and lights a fascia tell tale if a

problem is detected.  Information stored in the computer's memory may be accessed via a hand held electronic
scanner, in order to facilitate diagnosis of system faults (see later).

JJ.2 - TELL TALE LAMPS

Two tell tale lamps are provided in the instrument cluster to warn of problems in the brake system.

Brakes Tell Tale

As a bulb check function, this tell tale will glow red for about six seconds after ignition switch on, and then

go out unless one of the following conditions applies:
i) The parking brake is applied.
ii) The brake fluid level in the master cylinder reservoir is low.

Under normal circumstances, the tell tale should light when the ignition is switched on, and go out when

the parking brake is released.  If the lamp stays on, or comes on whilst driving, the car should be stopped
immediately, as this may be an indication of low brake fluid level caused by a hydraulic leak.  A button on the
reservoir cap allows the tell tale circuit to be tested.

ABS Tell Tale

The ABS tell tale warns the driver of problems in the anti-lock system.  The lamp should light for about 6

seconds following ignition switch on, and then go out.  If the lamp remains lit, or comes on whilst driving, a fault
in the ABS is indicated.  The base brake system will continue to operate normally, but without ABS regulation.
The car can be driven but should be checked and repaired at the earliest opportunity.

JJ.3 - BRAKE FLUID CHECK & CHANGE

Before checking the brake fluid level, ensure that the car is parked on a level surface, and remove the

driver's side front body access panel.  The level of fluid in the reservoir may be inspected without disturbing the
filler cap, and should be level with the top of the 'MAX' mark moulded on the translucent reservoir body.  The
level will fall progressively as the brake pads wear in service, and should be checked at each service interval.
A  sensor incorporated into the filler cap will light a tell tale lamp in the instrument cluster if the level drops
significantly.  As a bulb check, the tell tale should light for about six seconds when the ignition is first turned on,
but may also be tested by pressing the button on the filler cap, which action should light the tell tale with the
ignition switched on.

The reservoir is mounted on a bracket over the master cylinder to which it is connected by flexible hoses.

An internal baffle divides the reservoir into two compartments, with one section supplying the front brake
circuit, and a second section supplying the rear brakes in addition to, via another flexible hose, the clutch
master cylinder.  Service wear of the clutch friction plate will cause fluid to be displaced from the self adjusting
clutch slave cylinder, back to the reservoir, and will counteract to some extent the dropping of the level due to
brake pad wear.

Euro spec.

'Brakes' tell tale

USA spec.

'Brakes' tell tale

'ABS' tell tale

'ABS' tell tale

m252

   Lotus Service Notes

                Section JJ

Page 5

If the reservoir needs topping up, first clean around the cap to reduce the possibility of contamination

before unscrewing the cap;  it is not necessary to disconnect the level sensor cables.  Take suitable precautions
to guard against damage to paintwork caused by brake fluid dripping from the level sensor.  Use only a fresh
supply of DOT 4 non-mineral type fluid, identified by a yellow and black symbol.

Do NOT use DOT 5 silicone fluid, or any

fluid which has been exposed to the atmos-
phere for more than a brief period, or any fluid
suspected of being wet, dirty or contaminated.
Do not overfill.  Replace the filler cap securely.

Some service operations, such as replacing brake pads, will result in the displacement of fluid from the

hydraulic circuit back into the reservoir.  In order to prevent fluid overflowing from the reservoir, it may be
necessary to remove some fluid using a syringe.

Renewal of Brake Fluid

Brake fluid absorbs water from the atmosphere over a period of time (hygroscopical), resulting in a

lowering of the boiling point of the fluid, and corrosion of the hydraulic system.  For optimum safety and brake
performance, the brake fluid should be renewed every twelve months (including clutch release system).

Brake Bleeding Procedure

If the brake fluid is to be renewed, or an hydraulic component replaced, the system should be bled of air

using the following procedure:
1.

Using conventional manual techniques, or low air pressure applied to the reservoir, bleed the system
from each calliper bleed nipple in turn until no air bubbles can be seen.

2.

Connect the Lotus Scan tool and select ABS and follow the brake bleeding instructions.  Whilst this
automatic process is taking place (with all 4 calliper nipples open), gently cycle the brake pedal up and
down whilst keeping the reservoir topped up, to move any air bubbles displaced from the ABS unit down
the hydraulic lines.  Finish by closing each nipple with the pedal down.

3.

Repeat step (1) to purge each calliper feed line in turn.

JJ.4 - FRONT BRAKE PAD REPLACEMENT

Pad thickness may be checked with the wheel removed without disturbing the calliper.

Standard pad thickness (excluding backplate);

9.0 mm

Minimum pad thickness (excluding backplate);

2.5 mm

If the thickness of any pad is below the specified minimum, the axle set of pads should be renewed.  Note

that the pad backplates are factory fitted with anti-squeal overlays, and are identified with T 4139 on the
backplate.

For cars used on track, where sustained hard use and extreme brake temperatures are likely to occur,

'Motorsport' pads made by Pagid may be fitted in complete vehicle sets under part number A111J0150S (front)
and A111J0151S (rear).

1.

To remove the brake pads;  Remove the 'R' clip from the lower of the two pad retaining pins, and withdraw
the lower of the pin taking care to restrain the anti-rattle spring.  Remove the second retaining pin to-
gether with the anti-rattle spring plate.  Withdraw the pads from the calliper.  Measure the lining thickness
and renew the axle set of pads if any lining is below 2.5 mm.

j146

BRAKE FLUID

ohs139

RESERVOIR
CAP

Non-mineral type
brake fluid symbol
(Yellow & Black)

 

   Lotus Service Notes                                  Section JJ

Page 6

2.

Before replacing the pads, inspect the calliper for any signs of fluid leakage from a piston seal or joint,
and replace the calliper if any such signs are evident.  Clean the pad recess in the calliper taking suitable
precautions to protect from dust inhalation.

3.

If refitting the existing brake pads, refit each pad in the same position as originally fitted.

4.

If fitting new pads, the pistons must be pushed back into the calliper to provide the necessary clearance.
This action will return fluid to the master cylinder such that some fluid may need to be removed in order
to prevent overflowing.  Take care to avoid damaging the brake disc surface, or distorting the disc.

5.

Position the pads in the calliper, and insert the upper pad retaining pin from the outboard side.  Secure
with the split pin.

6.

Fit the anti-rattle spring into position with the side tangs pressing against the top end of the pad backplates,
and the centre tang beneath the retaining pin.  Insert the second pad retaining pin into the calliper,
passing over the lower central anti-rattle spring tongue.

7.

Before driving the car, press the brake pedal several times to bring the pads to their correct running
position.   Top up the master cylinder reservoir if necessary to bring the level to the top of the 'MAX' mark.

8.

Ensure the customer is made aware that 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.

JJ.5 - REAR BRAKE PAD REPLACEMENT

Pad thickness may be checked after removing the road wheel, without disturbing the calliper.
Standard pad thickness (excluding backplate);

6.5 mm

Minimum pad thickness (excluding backplate);

2.5 mm

If the thickness of any pad is below the specified minimum, the axle set of pads should be renewed.

Note that the pad backplates are marked T 4139 and are factory fitted with anti-squeal overlays.

'R' pin

Brake pad

Pad securing pin

Anti-rattle spring plate

         j164