Ford Falcon. Manual — part 55

205-02B-5

Independent Rear Suspension — Full Floating Axle

205-02B-5

DESCRIPTION AND OPERATION (Continued)

LSDs. All M78 final drive units should be filled

to rotation, providing torque transfer to the rear wheel

with synthetic oil as per Part 4-5 Specifications.

with the least traction.

Conventional M78 differentials are fitted with a

With a conventional differential, when the rear wheels

metal tag marked "HIGH PERFORMANCE. USE

are under extreme unbalance tractive conditions, such

APPROVED LUBRICANT ONLY" that is attached as one wheel on dry road and the other in mud or ice,

under the filler plug on the rear cover. For Limited wheel spin will occur if over acceleration is attempted.

Slip Differentials (LSD) units, the metal tag is

However, with the limited slip differential, when the

marked "LSD - HIGH PERFORMANCE. USE

tendency for wheel spin occurs, the friction generated

APPROVED LUBRICANT ONLY".

between the cones and the differential case (M78) or

M86 final drive units are fitted with 3.23 or 3.46

between the friction plates (M86) transfers a portion of

8.6" (220mm) diameter gear sets, with or without

the driving torque to the non-spinning wheel.

LSDs. M86 final drive units are fitted to all sedan

NOTE: For M78 LSDs: In the event of continued

vehicles powered by a V8 or turbo I6 engine. All

spinning a whirring sound is produced due to

M86 final drive units should be filled with mineral

over-running of the cones; such a condition or sound

oil as per Part 4-5 Specifications. Conventional

does not indicate failure of the unit.

M86 differentials are not fitted with a metal tag.

For LSD units, a metal tag marked "SPIN

RESISTANT DIFF. USE APPROVED

LUBRICANT ONLY" is attached under the filler

plug on the rear cover.

NOTE: Upgrading the lubricating oil to synthetic type

is recommended for vehicles fitted with a M86 final

drive unit where the vehicle will be regularly used for

towing.

This axle is a hypoid type of unitised carrier

construction. The two pinion differential case and the

drive pinion are mounted in opposed taper roller

bearings in the carrier. Differential bearing preload

adjustment is provided by the screw adjusters. Pinion

bearing preload is regulated by a collapsible spacer

and adjusted using the pinion nut.
Torque is transferred from the propshaft to the final

drive assembly via the constant velocity type

companion flange that is splined to the hypoid pinion.

The torque is then transferred from the pinion through

the ring gear, differential case, differential pinion cross

shaft, differential pinions and side gears to the

constant velocity joint halfshafts for conventional

differentials.
Halfshaft end play is pre-set and is not adjustable. Oil

seals are located between the haflshafts and the

screw adjusters.
M78 Limited Slip Differentials (LSDs), the differential

case houses two cone type clutches behind the side

gears. These cones are splined to the halfshafts, their

tapered faces bearing on the differential case. Thrust

springs pre-load the gears and cones, forcing the

tapered face of the cones into contact with the

differential case. The partial locking action due to the

spring load on the cones is automatically increased by

the inherent separating forces between the side gears

and pinion. This locking action directs a portion of the

driving force to the wheel with the least traction. M86

LSDs transfer torque in a similar manner as M78

LSDs, except that a multiplate oil bath type design is

utilised where alternate plates are splined to the

differential case and side gear. Compressive

preloading of the plates provides frictional resistance

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205-02B-6

Independent Rear Suspension — Full Floating Axle

205-02B-6

DESCRIPTION AND OPERATION (Continued)

M78 IRS Drive Unit

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205-02B-7

Independent Rear Suspension — Full Floating Axle

205-02B-7

DESCRIPTION AND OPERATION (Continued)

M86 IRS Drive Unit

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205-02B-8

Independent Rear Suspension — Full Floating Axle

205-02B-8

GENERAL PROCEDURES

Drive Unit Oil Change

Differential Case Preload Setting

1. Raise the vehicle so that it remains level.

1. Hold the differential case in position while

inserting screw adjusters until the differential is

2. Remove the bottom rear cover flanged bolt from

supported by the bearings. Use special tool

the drive unit to drain oil.

205-463 to fit the screw adjusters.

NOTE: It is preferable to drain the oil while it is

warm so that any debris can drain out more

easily.

3. Refit the cover bolt and tighten to 23-31 Nm.
4. Remove the lubrication tag, gasket and filler plug

(located on the left-hand side of the drive unit

housing ahead of the axle shaft).

5. Fill drive unit with 1.6 litres of the appropriate

lubricant.

6. Check the condition of the gasket to ensure

proper oil sealing function of filler plug.

7. Replace lubrication tag, gasket and filler plug and

tighten to 23-31 Nm.

In Vehicle Torque Check

2. Rotate the differential several times to seat

bearings while the screw adjusters are being

Torque Testing

tightened.

1. To test the Limited Slip differential for correct

3. Measure the bearing preload.

operation proceed as follows:

4. Tighten the screw adjusters until the bearing

1. Drive vehicle 10 km to warm up axle oil.

preload is within the required range. Record the

torque required on the screw adjusters to obtain

2. Raise one rear wheel and attach the Special

the required preload.

Tool No. E6662.

3. Place the transmission in neutral and release

Backlash and Tooth Contact Setting

the park brake.

1. Replace the differential assembly using the

4. Ensure that there is no brake drag affecting

spacers selected earlier.

wheel rotation.

2. Ensure that the pinion nut and bearing cap bolts

5. Chock the front wheels.

are tightened to the specified torque.

6. Attach a torque meter to the special tool, and

3. Check the backlash on the ring gear as described

rotate the axle.

in Section 205-00.

4. If backlash is excessive decrease the size of the

spacer on the pinion side of the ring gear and

increase the gear side spacer by the same

amount by turning the screw adjusters. If the

backlash is insufficient increase the size of the

spacer on the pinion side and decrease the size

of the spacer on the ring gear side by the same

amount by turning the screw adjusters.
NOTE: The total thickness of both spacers should

not change.

5. Recheck the tooth contact pattern as described in

Section 205-00.

6. Make necessary adjustments until tooth contact is

appropriate.

7. The torque required to rotate the axle shaft for

7. Replace/Install new seals and silicone sealant

a used L.S.D. unit should be between 50 and

that are not already in place.

130 Nm. Reading should be steady within 6

Nm.

8. Install rear cover and torque to specification.

8. If the torque required to continuously rotate

the wheel is outside the specification check

the differential for improper assembly and/or

rework.

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