1990 BMW 3 SERIES torque

12If the outer surface of the fitting that
mates with the hose is deteriorated (corroded,
pitted, etc.), it may be damaged further by
hose removal. If it is, a new thermostat
housing cover will be required.
13Remove the bolts and detach the housing
cover. If the cover is stuck, tap it with a soft-
faced hammer to jar it loose. Be prepared for
some coolant to spill as the gasket seal is
broken.
14Note how it’s fitted, then remove the
thermostat.
15Stuff a rag into the engine opening, then
remove all traces of old gasket material (if the
gasket is paper type). Otherwise, remove the
rubber O-ring (see illustration)and sealant
from the housing and cover with a gasket
scraper. Remove the rag from the opening
and clean the gasket mating surfaces.
16Fit the new thermostat and gasket in the
housing. Make sure the correct end faces out
- the spring end is normally directed towards
the engine.
17Refit the cover and bolts. Tighten the
bolts to the torque listed in this Chapter’s
Specifications.
M40 engines
18Remove the cooling fan and timing belt
upper cover.
19Unscrew the hose clamp and detach thebottom hose from the elbow on the front of
the cylinder head.
20Unbolt the elbow from the cylinder head.
Note the fitted position of the thermostat, then
remove it (see illustrations). Remove the
rubber O-ring; a new one will be needed for
reassembly.
21Locate the thermostat in the cylinder head
in the same position as noted during removal
(arrow pointing upwards).
22Press a new O-ring in the groove, and
locate the elbow on the cylinder head. Tighten
the bolts.
23Connect the bottom hose to the elbow,
and tighten the hose clamp.
24Refit the upper timing belt cover and
cooling fan.
All models
25Refill the cooling system (see Chapter 1).
26Connect the battery negative cable.
27Start the engine and allow it to reach
normal operating temperature, then check for
leaks and proper thermostat operation (as
described earlier in this Section).
4 Radiator-
removal and refitting
1
Warning: Wait until the engine is
completely cool before beginning
this procedure.Note: If the radiator is being removed because
it is leaking, note that minor leaks can often be
repaired without removing the radiator, using
a radiator sealant.
Caution: If the radio in your
vehicle is equipped with an anti-
theft system, make sure you
have the correct activation code
before disconnecting the battery.
Note: If, after connecting the battery, the
wrong language appears on the instrument
panel display, refer to page 0-7 for the
language resetting procedure.
Removal
1Disconnect the battery negative cable.
2Drain the cooling system (see Chapter 1). If
the coolant is relatively new, or in good
condition, save it and re-use it.
3Loosen the hose clamps, then detach the
hoses from the radiator (see illustrations). If
they’re stuck, grasp each hose near the end
with a pair of water pump pliers, twist gently
to break the seal, then pull off - be careful not
to distort or break the radiator outlets! If the
hoses are old or deteriorated, cut them off
and refit new ones.
4On M20 and M30 engines, disconnect the
reservoir hose from the radiator filler neck.
5Remove the screws or plastic fasteners that
attach the shroud to the radiator, and slide the
shroud towards the engine (see illustration).
On some engines it is possible to completely
remove the shroud.
6If the vehicle has automatic transmission,
Cooling, heating and air conditioning systems 3•3
3.20b Removing the thermostat
(M40 engine)3.20a Removing the elbow from the
cylinder head (M40 engine)3.15 On M20 and M30 engine models,
after the housing and thermostat have
been removed, take the O-ring out of the
housing and clean the recess in the
housing to be sure of a good seal upon
reassembly
4.5 Plastic fastener retaining the radiator
shroud on some engines4.3b Bottom hose connection to the
radiator4.3a Disconnecting the top hose from the
radiator
3

M20 engine
9Remove the distributor cap and HT leads,
ignition rotor and dust shield (see Chapter 1).
10Where applicable, remove the timing
sensor (see Chapter 5).
11Remove the timing belt upper cover (see
Chapter 2A).
12Loosen all three water pump mounting
bolts. Remove the top and right-hand side
bolts, but DON’T remove the lower bolt (see
illustration).
13Rotate the pump downwards, and remove
the drivebelt tensioner spring and pin.
14 Remove the final water pump bolt, and
remove the pump.
Caution: Leave the tensioner bolt
tight. Be careful to not move the
camshaft gear, as damage can
occur if the valves are moved.
M30 engine
15Remove the engine lifting bracket.
16Remove the bolts that mount the water
pump to the engine block.
17Remove the water pump, and recover the
gasket.
M40 engine
18Unscrew the mounting bolts and remove
the water pump. If the pump is tight in the
cylinder head, insert two bolts in the special
lugs at the top and bottom of the pump, and
tighten them evenly to press the pump out of
the head (see illustrations).
Refitting
19Clean the bolt threads and the threaded
holes in the engine to remove corrosion and
sealant.
20Compare the new pump to the old one, to
make sure they’re identical.
21Remove all traces of old gasket material
from the engine with a gasket scraper.
22Clean the water pump mating surfaces.
23On the M40 engine, locate a new O-ring
on the pump (see illustration).
24Locate the gasket on the pump, and offer
the pump up to the engine (see illustration).
Slip a couple of bolts through the pump
mounting holes to hold the gasket in place.
25Carefully attach the pump and gasket to
the engine, threading the bolts into the holes
finger-tight.Note:On the M20 engine, refit the
lower bolt finger-tight, then rotate the water
pump into position with the drivebelt tensioner
spring and pin in position.
26Refit the remaining bolts (if they also hold
an accessory bracket in place, be sure to
reposition the bracket at this time). Tighten
them to the torque listed in this Chapter’s
Specifications, in quarter-turn increments.
Don’t overtighten them, or the pump may be
distorted.
27Refit all parts removed for access to the
pump.
28Refill the cooling system and check the
drivebelt tension (see Chapter 1). Run the
engine and check for leaks.8 Coolant temperature sender
unit- check and renewal
2
Warning: Wait until the engine is
completely cool before beginning
this procedure.
1The coolant temperature indicator system
is composed of a temperature gauge
mounted in the instrument panel, and a
coolant temperature sender unit that’s
normally mounted on the thermostat housing
(see illustration 3.11). Some vehicles have
more than one sender unit, but only one is
used for the temperature gauge. On the M40
engine, the sender unit is mounted on the left-
hand side of the cylinder head, towards the
rear.
2If the gauge reading is suspect, first check
the coolant level in the system. Make sure the
wiring between the gauge and the sending
unit is secure, and that all fuses are intact. (If
the fuel gauge reading is suspect as well, the
problem is almost certainly in the instrument
panel or its wiring.)
3Before testing the circuit, refer to the
relevant wiring diagrams (see Chapter 12).
Where the sender unit simply earths out the
circuit, test by earthing the wire connected to
the sending unit while the ignition is on (but
without the engine running, for safety). If the
gauge now deflects to the end of the scale,
renew the sender unit. If the gauge does not
respond satisfactorily, the gauge, or the wiring
to the gauge, is faulty. Where the sender unit
has two terminals, test the circuit by checking
the resistance of the unit. No figures were
available at the time of writing, but typically
readings of several hundred or several
thousand ohms (depending on temperature)
would be expected. A reading of zero (short-
circuit) or infinity (open-circuit) would indicate
a faulty sender unit.
Caution: Do not earth the wire
for more than a second or two, or
damage to the gauge could
occur.
3•6 Cooling, heating and air conditioning systems
7.24 New outer gasket on the M40 engine
water pump7.23 Fit a new O-ring on the M40 engine
water pump
7.18b . . . and remove the water pump
(M40 engine)7.18a With the water pump mounting bolts
removed, screw two bolts into the special
lugs (one top and one bottom) . . .7.12 Water pump bolt locations on the
M20 engine

Carburettor (Solex 2BE)
Main jet
Stage 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . X120
Stage 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . X110
Air correction jet
Stage 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140
Stage 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
Venturi diameter
Stage 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 mm
Stage 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 mm
Idle fuel jet
Stage 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47.5 mm
Idle air jet
Stage 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180
Float needle valve diameter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.0 mm
Throttle positioner coil resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.97 to 1.63 ohms
Intake air temperature resistance
-10º C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8200 to 10 500 ohms
20º C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2200 to 2700 ohms
80º C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300 to 360 ohms
Float level
Stage 1 float chamber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27.0 to 29.0 mm
Stage 2 float chamber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29.0 to 31.0 mm
Fuel pressure checks (carburettor engines)
Fuel pump delivery pressure (engine idling) . . . . . . . . . . . . . . . . . . . . . . 0.1 to 0.3 bars
Fuel pressure checks (fuel injection engines)
Fuel system pressure (relative to intake manifold pressure)
3-Series (E30)
316i with M40/B16 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.0 ± 0.06 bars
318i with M10/B18 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5 to 3.0 bars
318i with M40/B18 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.0 ± 0.06 bars
320i with M20/B20 engine (L-Jetronic) . . . . . . . . . . . . . . . . . . . . . . 2.5 to 3.0 bars
320i with M20/B20 engine (Motronic) . . . . . . . . . . . . . . . . . . . . . . . 2.5 ± 0.05 bars
325i with M20/B25 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.0 ± 0.05 bars
5-Series (E28/”old-shape”)
All models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5 to 3.0 bars
5-Series (E34/”new-shape”)
518i with M40/B18 engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.0 ± 0.06 bars
All other models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5 to 3.0 bars
Fuel system hold pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1 bars
Fuel pump maximum pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3 to 6.9 bars
Fuel pump hold pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.5 bars
Transfer pump pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.28 to 0.35 bars
Injectors
Injector resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14.5 to 17.5 ohms
Accelerator cable free play . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.0 mm
Torque wrench settingsNm
Carburettor mountings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Fuel pump to cylinder head . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Throttle body nuts/bolts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 to 26
4•2 Fuel and exhaust systems
1 General information
With the exception of early models (316 and
518 models) all engines are equipped with
electronic fuel injection.
Early 316 and 518 models are equipped
with Solex carburettors. The carburettor fitted
is either a Solex 2B4 (early models) or
2BE (later models). The mechanical fuel pumpis driven by an eccentric lobe on the
camshaft.
Fuel injection models are equipped with
either the L-Jetronic or the Motronic fuel
injection system. From 1988, fuel injection
models are equipped with an updated version
of the Motronic system - this system is easily
distinguished from the earlier system by the
absence of a cold start injector. The electric
fuel pump is located beneath the rear of the
vehicle, or inside the fuel tank. The fuel pump
relay on Motronic systems is activated from aearth signal from the Motronic control unit
(ECU). The fuel pump operates for a few
seconds when the ignition is first switched on,
and it continues to operate only when the
engine is actually running.Air intake system
The air intake system consists of the air
filter housing, the airflow meter and throttle
body (fuel injection models), and the intake
manifold. All components except the intake
manifold are covered in this Chapter; for

19Depressurise the fuel system (see Sec-
tion 2).
20Detach the battery negative cable.
Caution: If the radio in your
vehicle is equipped with an anti-
theft system, make sure you
have the correct activation code
before disconnecting the battery. Refer to
the information on page 0-7 at the front of
this manual before detaching the cable.
Note: If, after connecting the battery, the
wrong language appears on the instrument
panel display, refer to page 0-7 for the
language resetting procedure.
21Detach the fuel feed hose from the fuel
rail, and attach a fuel pressure gauge directly
to the hose. Note:If the tee fitting is still
connected to the gauge, be sure to plug the
open end.
22Reconnect the battery.
23Using a jumper wire, bridge the terminals
of the fuel pump relay.
24Turn the ignition switch on to operate the
fuel pump.
25Note the pressure reading on the gauge,
and compare the reading to the fuel pump
pressure listed in this Chapter’s Specifica-
tions.
26If the indicated pressure is less than
specified, inspect the fuel line for leaks
between the pump and gauge. If no leaks are
found, renew the fuel pump.
27Turn the ignition off and wait five minutes.
Note the reading on the gauge, and compare
it to the fuel pump hold pressure listed in this
Chapter’s Specifications. If the hold pressure
is less than specified, check the fuel lines
between the pump and gauge for leaks. If no
leaks are found, renew the fuel pump.
28Remove the jumper wire. Relieve the fuel
pressure by opening the bleed valve on the
gauge and directing the fuel into a suitable
container. Remove the gauge and reconnect
the fuel line.
Transfer pump pressure check
29Depressurise the fuel system (see Sec-
tion 2).
30Detach the battery negative cable.
Caution: If the radio in your
vehicle is equipped with an anti-
theft system, make sure you
have the correct activation code
before disconnecting the battery. Refer to
the information on page 0-7 at the front of
this manual before detaching the cable.
Note: If, after connecting the battery, the
wrong language appears on the instrument
panel display, refer to page 0-7 for the
language resetting procedure.
31Remove the transfer pump access plate
(on some models, it’s located under the rear
seat cushion - on others, it’s located under
the carpet in the luggage compartment).
Disconnect the output hose from the transfer
pump, and connect a fuel pressure gauge to
the outlet pipe.
32Reconnect the battery.33Using a jumper wire, bridge the terminals
of the fuel pump relay.
34Turn the ignition switch on to operate the
fuel pump.
35Note the pressure reading on the gauge,
and compare to the value listed in this
Chapter’s Specifications.
36If the indicated pressure is less than
specified, renew the transfer pump.
Fuel pump relay check
37Switch on the ignition.
38Using a voltmeter, probe the following
terminals from the back of the relay electrical
connector. Check for battery voltage at
terminal 30 (M20 and M30 engines) or
terminal 15 (M10 and M40 engines). Note:If
there is no voltage on models with luggage
compartment-mounted batteries, check for a
faulty fusible link. The 50-amp link is about
6 inches from the battery, in a black wire.
39Turn the ignition off, and disconnect the
relay from the electrical connector. Using a
voltmeter, probe the connector terminals that
correspond to fuel pump relay pins 85 (-) and
86(+) on M20 and M30 engines, or terminal 50
and earth on M10 and M40 engines. Have an
assistant turn the engine over on the starter,
and observe the voltage reading. Battery
voltage should be indicated.
40If there is no voltage, check the fuse(s)
and the wiring circuit for the fuel pump relay. If
the voltage readings are correct, and the fuel
pump only runs with the jumper wire in place,
then renew the relay.
41If the fuel pump still does not run, check
for the proper voltage at the fuel pump
terminals (see Section 4). If necessary, renew
the fuel pump.
4 Fuel pump, transfer pump
and fuel level sender unit-
removal and refitting
2
Warning: Fuel is extremely
flammable, so take extra
precautions when you work on
any part of the fuel system. Don’t
smoke, or allow open flames or bare light
bulbs, near the work area. Also, don’t work
in a garage where a natural gas-type
appliance with a pilot light is present.
Fuel pump (carburettor engines)
1Disconnect the battery negative cable.
Disconnect both hoses from the pump, and
unscrew and remove the two securing nuts
(see illustration).
2Carefully withdraw the pump from the
cylinder head. If it’s stuck, a slight downward
tap on the thick insulating distance piece with
a piece of wood, should free it.
3Remove the two thin gaskets.
4The fuel pump is a sealed unit, and it is not
possible to renew any of the internal
components. Should an internal fault occur, it
must be renewed complete.5Refitting is a reversal of the removal
procedure, but renew the thin gaskets each
side of the insulating distance piece, and
tighten the fuel pump down evenly to the
torque stated in the Specifications. On no
account alter the thickness of the distance
piece, or the correct operation of the fuel
pump will be upset.
Fuel pump (fuel injection
engines)
Note 1: The electric fuel pump is located
inside the fuel tank on later models with the
Motronic system, or adjacent to the fuel tank
on the L-Jetronic system. The early models
are also equipped with a transfer pump
located in the fuel tank. The transfer pump
feeds the larger main pump, which delivers
the high pressure required for proper fuel
system operation.
Note 2: The fuel level sender unit is located in
the fuel tank with the transfer pump on early
models, or with the main fuel pump on later
models.
6Depressurise the fuel system (see Sec-
tion 2) and remove the fuel tank filler cap to
relieve pressure in the tank.
7Disconnect the battery negative cable.
Caution: If the radio in your
vehicle is equipped with an anti-
theft system, make sure you
have the correct activation code
before disconnecting the battery. Refer to
the information on page 0-7 at the front of
this manual before detaching the cable.
Note: If, after connecting the battery, the
wrong language appears on the instrument
panel display, refer to page 0-7 for the
language resetting procedure.
Externally-mounted fuel pump
8Raise and support the vehicle.
9Remove the two rubber boots that protect
the fuel pump connectors, and disconnect the
wires from the pump (see illustration).
10Using hose clamps, pinch shut the fuel
hoses on each side of the fuel pump. If you
don’t have any hose clamps, wrap the hoses
with rags, and clamp them shut with self-
locking pliers, tightened just enough to
prevent fuel from flowing out.
11Disconnect the hoses from the pump.
12Remove the fuel pump mounting screws
Fuel and exhaust systems 4•5
4.1 Fuel pump on carburettor engines
4

17 Throttle body- check,
removal and refitting
2
Check
1Detach the air intake duct from the throttle
body (see Section 8) and move the duct out of
the way.
2Have an assistant depress the throttle
pedal while you watch the throttle valve.
Check that the throttle valve moves smoothly
when the throttle is moved from closed (idle
position) to fully-open (wide-open throttle).
3If the throttle valve is not working properly,
renew the throttle body unit.
Warning: Wait until the engine is
completely cool before beginning
this procedure.
Caution: If the radio in your
vehicle is equipped with an anti-
theft system, make sure you
have the correct activation code
before disconnecting the battery. Refer to
the information on page 0-7 at the front of
this manual before detaching the cable.
Note: If, after connecting the battery, the
wrong language appears on the instrument
panel display, refer to page 0-7 for the
language resetting procedure.
Removal and refitting
4Detach the battery negative cable.
5Detach the air intake duct from the throttle
body, and place to one side.
6Detach the accelerator cable from the
throttle body (see Section 9).
7Detach the cruise control cable, if applicable.
8Clearly label all electrical connectors
(throttle position sensor, cold start injector,
idle air stabiliser, etc), then unplug them.
9Clearly label all vacuum hoses, then detach
them.
10Unscrew the radiator or expansion tank
cap to relieve any residual pressure in the
cooling system, then refit it. Clamp shut the
coolant hoses, then loosen the hose clamps
and detach the hoses. Be prepared for some
coolant leakage.11Remove the throttle body mounting nuts
(upper) and bolts (lower), and detach the
throttle body from the air intake plenum (see
illustration).
12Cover the air intake plenum opening with
a clean cloth, to prevent dust or dirt from
entering while the throttle body is removed.
13Refitting is the reverse of removal. Be sure
to tighten the throttle body mounting nuts to
the torque listed in this Chapter’s Specifica-
tions, and adjust the throttle cable (see
Section 9) on completion.
18 Fuel pressure regulator-
check and renewal
3
Warning: Fuel is extremely
flammable, so take extra
precautions when you work on
any part of the fuel system. Don’t
smoke, or allow open flames or bare light
bulbs, near the work area. Don’t work in a
garage where a natural gas-type appliance
(such as a water heater or clothes dryer)
with a pilot light is present. If you spill any
fuel on your skin, rinse it off immediately
with soap and water. When you perform
any kind of work on the fuel system, wear
safety glasses, and have a fire
extinguisher on hand.
Caution: If the radio in your
vehicle is equipped with an anti-
theft system, make sure you
have the correct activation code
before disconnecting the battery. Refer to
the information on page 0-7 at the front of
this manual before detaching the cable.
Note: If, after connecting the battery, the
wrong language appears on the instrument
panel display, refer to page 0-7 for the
language resetting procedure.
Check
1Depressurise the fuel system (see Sec-
tion 2).
2Detach the battery negative cable.
3Disconnect the fuel line and connect a fuel
pressure gauge (see Section 3). Reconnect
the battery.4Pressurise the fuel system (refit the fuel
pump fuse and switch on the ignition), and
check for leakage around the gauge
connections.
5Connect a vacuum pump to the fuel
pressure regulator (see illustration).
6Run the fuel pump (see Section 3). Read the
fuel pressure gauge with vacuum applied to
the pressure regulator, and also with no
vacuum applied. The fuel pressure should
decrease as vacuum increases.
7Stop the fuel pump and reconnect the
vacuum hose to the regulator. Start the engine
and check the fuel system pressure at idle,
comparing your reading with the value listed
in this Chapter’s Specifications. Disconnect
the vacuum hose and watch the gauge - the
pressure should jump up to maximum as soon
as the hose is disconnected.
8If the fuel pressure is low, pinch the fuel
return line shut and watch the gauge. If the
pressure doesn’t rise, the fuel pump is
defective, or there is a restriction in the fuel
feed line. If the pressure now rises sharply,
renew the pressure regulator.
9If the indicated fuel pressure is too high,
stop the engine, disconnect the fuel return line
and blow through it to check for a blockage. If
there is no blockage, renew the fuel pressure
regulator.
10If the pressure doesn’t fluctuate as
described in paragraph 7, connect a vacuum
4•16 Fuel and exhaust systems
18.5 Carefully watch the fuel pressure
gauge as vacuum is applied (fuel pressure
should decrease as vacuum increases)
17.11 Remove the nuts (arrowed) and lift
the throttle body from the intake manifold
(the two lower bolts are hidden from view)16.11b Remove the nuts (arrowed) from
the air cleaner housing, and detach the
airflow meter16.11a Push the tab and remove the air
duct from inside the air cleaner assembly

Torque wrench settingsNm
Front disc brake caliper
Caliper guide (mounting) bolts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 to 35
Caliper bracket-to-strut housing bolts
3-Series, E30 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
5-Series, E28 (“old-shape”) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
5-Series, E34 (“new-shape”) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
Rear disc brake caliper
Caliper guide (mounting) bolts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 to 35
Carrier-to-trailing arm bolts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
Brake hose-to-caliper fitting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 to 17
Master cylinder-to-brake servo nuts
3-Series . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
5-Series . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 to 29
Brake servo mounting nuts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 to 24
Hydraulic line-to-hydraulic brake servo threaded
fittings - 5-Series, E28 (“old-shape”) . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Wheel bolts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . See Chapter 1
9•2 Braking system
1 General information
All 3-Series models, and 5-Series E28 (“old-
shape”) models, are equipped with front disc
brakes and either rear drum or rear disc
brakes. 5-Series E34 (“new-shape”) models
have disc brakes front and rear. Front and
rear brakes are self-adjusting on all models.
Some later models are equipped with an Anti-
lock Braking System (ABS); this is described
in Section 2.
Hydraulic system
The hydraulic system consists of two
separate circuits. The master cylinder has
separate reservoirs for the two circuits; in the
event of a leak or failure in one hydraulic
circuit, the other circuit will remain operative.
Brake servo
The vacuum brake servo, utilising engine
manifold vacuum and atmospheric pressure
to provide assistance to the hydraulically
operated brakes, is mounted on the bulkhead
in the engine compartment.
A hydraulic brake servo system is used on
5-Series E28 models. This system uses
hydraulic pressure from the power steering
pump to assist braking.
Handbrake
The handbrake operates the rear brakes,
and is cable-operated via a lever mounted in
the centre console. The handbrake assembly
on rear drum brake models is part of the rear
drum brake assembly, and is self-adjusting.
On rear disc brake models, the handbrake
uses a pair of brake shoes located inside the
centre portion of the rear brake disc, and is
manually-adjusted.
Brake pad wear warning system
The brake pad wear warning system is
linked to a red warning light in the instrumentcluster, which comes on when the brake pads
have worn down to the point at which they
require renewal. DO NOT ignore this reminder.
If you don’t renew the pads shortly after the
brake pad wear warning light comes on, the
brake discs will be damaged.
On some models, the brake pad wear
warning system also includes an early
warning light that comes on only when the
brake pedal is depressed, letting you know in
advance that the pads need to be renewed.
The wear sensor is attached to the brake
pads. The sensor is located at the left front
wheel; on some models, there is another
sensor at the right rear wheel. The wear
sensor is part of a closed circuit. Once the
pads wear down to the point at which they’re
flush with the sensor, the disc grinds away the
side of the sensor facing the disc. Thus, the
wire inside the sensor is broken, and the red
light on the instrument panel comes on.
Always check the sensor(s) when renewing
the pads. If you change the pads before the
warning light comes on, the sensor(s) may still
be good; once the light has come on, renew
the sensor.
Service
After completing any operation involving
dismantling of any part of the brake system,
always test drive the vehicle to check for
proper braking performance before resuming
normal driving. When testing the brakes, try to
select a clean, dry, road with no camber (ie as
flat as possible) and with no other traffic.
Conditions other than these can lead to
inaccurate test results.
Test the brakes at various speeds with both
light and heavy pedal pressure. The vehicle
should stop evenly, without pulling to one side
or the other. Avoid locking the brakes,
because this slides the tyres and diminishes
braking efficiency and control of the vehicle.
Tyres, vehicle load and wheel alignment are
factors which also affect braking
performance.
2 Anti-lock Braking system
(ABS)- general information
The Anti-lock Braking System is designed
to maintain vehicle control, directional stability
and optimum deceleration under severe
braking conditions on most road surfaces. It
does so by monitoring the rotational speed of
each wheel and controlling the brake line
pressure to each wheel during braking. This
prevents the wheels from locking up.
The ABS system has three main
components - the wheel speed sensors, the
electronic control unit, and the hydraulic
control unit. The sensors - one at each wheel
since 1985, but at both front wheels and one
at the rear differential on earlier models - send
a variable voltage signal to the control unit,
which monitors these signals, compares them
to its program information, and determines
whether a wheel is about to lock up. When a
wheel is about to lock up, the control unit
signals the hydraulic unit to reduce hydraulic
pressure (or not increase it further) at that
wheel’s brake caliper. Pressure modulation is
handled by electrically-operated solenoid
valves.
If a problem develops within the system, an
“ABS” warning light will glow on the
dashboard. Sometimes, a visual inspection of
the ABS system can help you locate the
problem. Carefully inspect the ABS wiring
harness. Pay particularly close attention to the
harness and connections near each wheel.
Look for signs of chafing and other damage
caused by incorrectly-routed wires. If a wheel
sensor harness is damaged, the sensor
should be renewed (the harness and sensor
are integral).
Warning: DO NOT try to repair an
ABS wiring harness. The ABS
system is sensitive to even the
smallest changes in resistance. Repairing
the harness could alter resistance values

6Be sure to inspect the wear sensor(s) (left
front wheel only, or left front and right rear
wheel). If they’re OK, transfer them from the
old pads to the new ones; if they’re worn by
abrasion, fit new sensors on the new pads.
7To fit the new pads, reverse the removal
procedure. When refitting the caliper, be sure
to tighten the mounting bolts to the torque
listed in this Chapter’s Specifications.
Warning: Check and if necessary
renew the mounting bolts on 3-
Series models whenever they are
removed. If in doubt, use new
bolts.
8After the job is completed, firmly depress
the brake pedal a few times, to bring the pads
into contact with the discs. The pedal shouldbe at normal height above the floor, and firm.
Check the level of the brake fluid, adding
some if necessary. Check carefully for leaks,
and check the operation of the brakes before
returning the vehicle to normal service.
9Avoid heavy braking as far as possible for
the first hundred miles or so until the new
pads have bedded in.
4 Disc brake caliper- removal,
overhaul and refitting
4
Warning: Dust created by the
brake system may contain
asbestos, which is harmful to
your health. Never blow it out
with compressed air, and don’t inhale any
of it. An approved filtering mask should be
worn when working on the brakes. Do not,
under any circumstances, use petroleum-
based solvents to clean brake parts. Use
brake system cleaner only!
Warning: Brake fluid is
poisonous. It is also an effective
paint stripper. Refer to the
warning at the start of Section 16.
Note:If an overhaul is indicated (usually
because of fluid leakage), explore all options
before beginning the job. Overhauled calipers
may be available on an exchange basis, which
makes this job quite easy. If you decide to
overhaul the calipers, make sure that anoverhaul kit is available before proceeding.
Always overhaul the calipers in pairs - never
overhaul just one of them.
Removal
1Loosen the wheel bolts, raise the front or
rear of the vehicle, and place it securely on
axle stands. Remove the wheel.
2If you’re just removing the caliper for
access to other components, it isn’t
necessary to detach the brake line. If you’re
removing the caliper for overhaul, disconnect
the brake line from the caliper, for preference
using a split ring (“brake”) spanner to protect
the fitting. Plug the line, to keep contaminants
out of the brake system and to prevent losing
brake fluid unnecessarily.
3Refer to Section 3 for the front or rear
caliper removal procedure - it’s part of the
brake pad renewal procedure. Note:The rear
caliper is similar in design to the front caliper
on 5-series models.
Overhaul
4On all calipers except the front calipers on
3-Series models, remove the circlip for the
dust seal (see illustration),then remove the
dust boot (see illustration). Before you
remove the piston, place a block of wood
between the piston and caliper to prevent
damage as it is removed.
5To remove the piston from the caliper,
apply compressed air to the brake fluid hose
connection on the caliper body (see
9•4 Braking system
3.5l Hang the caliper out of the way with a
piece of wire
3.5m Remove the outer brake pad - to fit
the new pads, reverse the removal
procedure
3.5k Unclip the inner brake pad from the
piston (5-Series)3.5j Remove the caliper and inner brake
pad (5-Series)
3.5i Depress the piston with a C-clamp
(5-Series)3.5h Prise off the anti-rattle spring
(5-Series)3.5g Remove the plugs for the brake
caliper mounting bolts, then remove the
bolts (5-Series)

adjusting screw and contract the handbrake
shoes (see illustration).
Refitting
7Ensure that the disc is completely clean
before refitting. If penetrating oil was used to
remove the disc, make sure that no trace of
this is present. Place the disc on the hub, and
refit the disc retaining screw. Tighten the
screw securely.
8Refit the caliper mounting bracket (if
removed), brake pads and caliper (see
Sections 3 and 4). Tighten all fasteners to the
torques listed in this Chapter’s Specifications.
9Refit the wheel, then lower the vehicle to
the ground. Depress the brake pedal a few
times to bring the brake pads into contact
with the disc.
10Adjust the handbrake shoes, if necessary
(Section 11).
11Check the operation of the brakes
carefully before returning the vehicle to
normal service.
6 Drum brake shoes- renewal
2
Warning: Brake shoes must be
renewed on both wheels at the
same time - never renew the
shoes on only one wheel. Also,
the dust created by the brake system may
contain asbestos, which is harmful to your
health. Never blow it out with compressed
air, and don’t inhale any of it. Always wear
an approved filtering mask when servicing
the brake system. Do not, under anycircumstances, use petroleum-based
solvents to clean brake parts. Use brake
system cleaner only.
Caution: Whenever the brake
shoes are renewed, new return
and hold-down springs and new
automatic adjuster thermo-clips
should also be fitted. Due to the
continuous heating/cooling cycle to which
the springs are subjected, they may lose
their tension over a period of time,
allowing the shoes to drag on the drum,
and wear at a much faster rate than
normal. When fitting new brake shoes, use
only original-equipment or high-quality
brand name parts.
Note 1:All four rear brake shoes must be
renewed at the same time, but to avoid mixing
up parts, work on only one brake assembly at
a time. Some rear brake components are
different for left and right-hand sides, so don’t
mix them up.
Note 2:If the wheel cylinder is found to be
leaking or otherwise defective, renew it after
removing the brake shoes. This is simply a
matter of disconnecting the hydraulic line and
unbolting the cylinder from the backplate.
Attempting to overhaul a leaking cylinder is
unlikely to be satisfactory, even if spare parts
are available.
1Chock the front wheels, then loosen the
rear wheel bolts, raise the rear of the vehicle
and place it securely on axle stands. Remove
the rear wheels and release the handbrake.
2Remove the drum retaining screw (see
illustration)and remove the drum. If the drum
is stuck to the hub, spray the area between
the hub and the drum with penetrating oil
(see illustration). If the drum still won’t come
off, the shoes have probably worn ridges into
the drum, and will have to be retracted. Insert
a narrow flat-bladed screwdriver through one
of the holes in the hub flange (see
illustration)and back off the adjuster wheel
until the drum can be removed.
3Inspect the drum for cracks, score marks,
deep scratches and hard spots, which will
appear as small discoloured areas. If the hard
spots can’t be removed with emery cloth or if
any of the other conditions exist, the drum must
be taken to a specialist to have the drum
resurfaced. Note:Professionals recommendresurfacing the drums whenever a brake job is
done. Resurfacing will eliminate the possibility
of out-of-round drums. If the drums are worn so
much that they can’t be resurfaced without
exceeding the maximum allowable diameter
(which is cast into the drum) (see illustration),
then new ones will be required. At the very least,
if you elect not to have the drums resurfaced,
remove the glazing from the surface with emery
cloth or sandpaper, using a swirling motion.
Braking system 9•7
6.2b If the drum is stuck to the hub, apply
penetrating oil around the hub/drum area,
and give it a few minutes to loosen up
any rust6.2a Removing the drum retaining screw5.6d If a rear disc still sticks to the hub,
insert a thin, flat-bladed screwdriver
through the hub flange, rotate the
starwheel on the handbrake adjusting
screw, and contract the handbrake shoes
(disc removed for clarity)
6.3 The maximum allowable inside
diameter of the drum is cast into the drum
6.2c If the brake shoes have worn a
groove in the drum and it won’t come off,
insert a thin flat-bladed screwdriver
through one of the wheel bolt holes in the
flange, and loosen the automatic adjuster
mechanism (for the sake of clarity, the
drum has already been removed in this
photo, and the screwdriver is being
inserted underneath the flange instead of
though a wheel bolt hole)
9
If the front disc is stuck, on
some discs it is possible to
thread two or three bolts into
the holes provided and
tighten them. Alternate between the
bolts, turning them a couple of turns at
a time, until the disc is free.