Ford Falcon. Manual — part 40

205-00-4

Driveline System — General Information

205-00-4

DESCRIPTION AND OPERATION (Continued)

a V8 or turbo I6 engine. All M86 beam axles

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

should be filled with mineral oil as per Part 4-5

does not indicate failure of the unit.

Specifications. Conventional M86 differentials are

not fitted with a metal tag. For LSD units, a metal

Run in

tag marked “SPIN RESISTANT DIFF. USE

It is recommended that the vehicle is driven

APPROVED LUBRICANT ONLY” is attached

conservatively for the first 1500kms from new, and

under the filler plug on the rear cover.

that towing is avoided during this period. This allows

NOTE: Upgrading the lubricating oil to synthetic type

the final drive to bed in correctly and helps assure

is recommended for vehicles fitted with a M86 final

satisfactory final drive component life. During the

drive unit where the vehicle will be regularly used for

run-in period, the vehicle should be driven at normal

towing. Refer to, Specifications of Section 205-02 for

road speeds (within the posted limits) as final drive

the recommended synthetic lubricant.

loading not vehicle speed is of primary importance.

These axle types are a hypoid type of unitised carrier

Towing

construction. The two pinion differential case and the

drive pinion are mounted in opposed taper roller

Ensure that the vehicle is fitted with a Ford approved

bearings in the carrier. Differential bearing preload

tow pack, and that the towing limits for the particular

adjustment is provided by the screw adjusters. Pinion vehicle as designated by Ford and relevant State

bearing preload is regulated by a collapsible spacer

regulatory bodies are adhered to. The final drive must

and adjusted using the pinion nut.

be filled to the correct level with the correct type of oil

to ensure satisfactory performance while towing.

Torque is transferred from the propshaft to the final

Overheating can occur where low oil level or the

drive assembly via the constant velocity type

wrong type of lubricant is used.

companion flange that is splined to the hypoid pinion.

The torque is then transferred from the pinion through

Oil Changes

the ring gear, differential case, differential pinion cross

shaft, differential pinions and side gears to the

If the vehicle is going to be used for towing on a

constant velocity joint halfshafts for conventional

regular basis, or occasional heavy towing, an oil

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

change after run-in is recommended. Note that this is

adjustable. Oil seals are located between the

not part of regular scheduled vehicle maintaince.

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

to rotation, providing torque transfer to the rear wheel

with the least traction.
With a conventional differential, when the rear wheels

are under extreme unbalance tractive conditions, such

as one wheel on dry road and the other in mud or ice,

wheel spin will occur if over acceleration is attempted.

However, with the limited slip differential, when the

tendency for wheel spin occurs, the friction generated

between the cones and the differential case (M78) or

between the friction plates (M86) transfers a portion of

the driving torque to the non-spinning wheel.
NOTE: (For M78 LSDs) In the event of continued

spinning a whirring sound is produced due to

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205-00-5

Driveline System — General Information

205-00-5

DIAGNOSIS AND TESTING

practical speed in top gear to 110 kilometres per hour

Driveline System

(or maximum legal speed), noting any noises and the

speeds at which they occur. Release the accelerator

In Vehicle Diagnostics

and without using the brakes allow the vehicle to lose

For other than obvious mechanical failures, careful

speed, again noting noise and speed. Next, allow the

tests should be made to locate final drive troubles

vehicle to coast to rest from 110 kph with the

since noises from engine, transmission and wheels

transmission in neutral position. Any noises common

may all be attributed to the final drive. A suggested

to earlier tests may be eliminated, as the final drive is

test routine is as follows:- Ensure that the axle

not under load in these conditions. Engine noise is

lubricant is correct and at the correct level. Drive at

gauged by gradually accelerating the engine with the

low speed until thoroughly familiar with vehicle noises vehicle at rest. Noises not eliminated at this stage are

by which time the rear axle assembly should have

most probably final drive gear noise.

warmed up. Accelerate gradually from the lowest

Symptom Chart

Symptom Chart

Condition

Source

Action

Worn brake rotor.

Rear Wheel Noise (Beam Axles)

Replace/Repair as required

Wheel bolts loose.
Brinnelled or scored bearings.
Insufficient lubrication.
Bent axle shaft or wheel.
Dragging brakes.
Axle shaft retainer plate loose.
Tyre defective.
Damaged or worn C.V. joints (IRS).

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205-00-6

Driveline System — General Information

205-00-6

DIAGNOSIS AND TESTING (Continued)

Condition

Source

Action

Bearing noise is usually fairly constant

Final Drive Noise

Replace/Repair as required

throughout the entire speed range and
of a pitch that increases in proportion
to vehicle speed.

NOTE: Final drive noises fall into two

categories: Gear Noise and Bearing
Noise.

Gear noise is of a periodic nature
being produced at various speeds on
drive, float, coast and cruise
conditions. If the pinion and ring gear
have been set up with too little
backlash a continuous whine may be
produced.

NOTE: Gear noise is most commonly

caused by:

Incorrect mesh of gear teeth (i.e.
incorrect pinion head positioning shim
or backlash setting shims).
Scored gear teeth - usually the result
of incorrect lubricant type or level.
End play in bearings.
Bruised or chipped teeth.
Excessive runout of pinion head or ring
gear backface.
Ring gear creeping on differential
housing resulting from ring gear bolts
loosening - noise from this source
usually appears as a sharp metallic
sound when shifting from reverse to
first gear.

NOTE: Bearing Noise is usually

caused by worn bearings and can be
the result of:

Contaminants in the lubricant.
Incorrect preload setting.
Bearings incorrectly mounted - e.g. dirt
trapped behind abutment faces during
assembly.

Rear Axle Shaft Breakage (Beam

Abnormal clutch operation.

Replace/Repair as required

Bent axle tubes/half shafts.

Axle)

Excessive vehicle loads.

Lubricant level incorrect.

Overheating of Final Drive Assembly

Replace/Repair as required

Incorrect lubricant type.
Incorrect run-in procedure.

Lubricant level too high.

Loss of Lubricant

Replace/Repair as required

Breather malfunction.
Damaged or worn oil seals.
Rear cover bolts / filler plug loose.
Rear cover flange distorted.
Rear cover gasket/sealant damaged or
incorrectly applied.
Split cover or tubes (beam axles).
Incorrect type of lubricant - can cause
foaming.
Loose drain plug, or sealant not
replaced on drain plug at refitting.

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205-00-7

Driveline System — General Information

205-00-7

DIAGNOSIS AND TESTING (Continued)

Condition

Source

Action

Worn axle shaft or halfshaft splines.

Excessive Backlash

Replace/Repair as required

Loose wheel nuts.
Loose universal or constant velocity
propshaft joint flange mountings.
Excessive backlash in either the
differential or hypoid gears.
Bearings worn or incorrectly adjusted.
Worn or loose constant velocity
halfshaft joints (IRS).

2. Increasing backlash moves the drive gear away

Bearing Noise

from the pinion:

Defective bearings can produce a whine that varies in

Drive pattern moves slightly higher and

proportion to vehicle speed. This will help distinguish

toward the heel.

between bearing and/or gear noise.

Coast pattern moves higher and toward the

1. Pinion bearing noise can be identified as a

heel.

constant grinding noise. Pinion bearings are

3. Thicker pinion shim with the backlash constant

rotating at a higher speed than differential side

moves the pinion closer to the driver gear.

bearings or axle shaft bearings. The noise is most

noticeable during light acceleration between 30 to

Drive pattern moves deeper on the tooth

40 km/h.

(flank contact) and slightly toward the toe.

2. Wheel bearing noise may be confused with rear

Coast pattern moves deeper on the tooth

axle noise. To differentiate between wheel

toward the heel.

bearings and rear axle, drive the vehicle on a

4. Thinner pinion shim with the backlash constant

smooth road at a medium low speed. With traffic

moves the pinion further from the drive gear:

permitting, turn the vehicle sharply right and left. If

Drive pattern moves toward the top of the

noise is caused by wheel bearings, the noise will

tooth (face contact) and toward the heel.

increase on the defective bearings because of

Coast pattern moves toward the top of the

side loading.

tooth and slightly toward the toe.

3. Side bearings will produce a constant grinding

If the patterns are not correct, make the changes as

noise of a slower nature than pinion bearing, (side

indicated.

bearing noise cannot be determined by the wheel

bearing test), but will be of a similar frequency as

When the pattern is correct, remove the marking

axle shaft bearings.

compound from the gear teeth. Regardless of all

previous measurements and other factors, the tooth

Gear Tooth Contact Pattern Check

contact pattern must be correct for successful rear

axle operation.

Paint the gear teeth with suitable gear marking

compound. Wrap a cloth around the drive shaft to act

The Ideal Tooth Pattern

as a brake. Rotate the ring gear back and forth (use a

box wrench on the drive gear attaching bolts for a

The ideal tooth pattern is not a rigid standard but

lever) until a clear tooth contact pattern is obtained

merely a general rule. In general, desirable tooth

(approximately 4 ring gear rotations in both

patterns should have the following characteristics:

directions).

The drive pattern should be fairly well centred on

After diagnosing the tooth pattern, make the

the tooth.

appropriate adjustments as explained in the following

The coast pattern should be centred on the tooth

pages. Drive and coast patterns indicating changes

but may be slightly toward the toe.

required to obtain the correct operating position of the

Some clearance between the pattern and the top

gears is illustrated in the “ideal tooth contact pattern

of the tooth is desirable.

on ring gear” diagram. The movement of tooth contact

patterns with changes in gear location can be

There should be no hard lines where the pressure

summarised as follows:

is high.

1. Decreasing backlash moves the drive gear closer The individual gear set need not conform exactly to

to the pinion:

the ideal pattern in order to be acceptable.

Characteristic differences between individual gear

Drive pattern (convex side of gear) moves

sets will result in patterns that are acceptable yet

slightly lower and toward the toe.

different from those illustrated.

Coast pattern (concave side of gear) moves

lower and toward the toe.

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