Land Rover Monthly – October 2019

146 LANDROVER MONTHLY http://www.britpart.com

T

HE suspensionA-framefi tted to

Discovery 1, Classic RangeRovers

and Defenders (includingearly

Ninety and OneTens) helpsto

locate therear axle position inrelationto

the chassis. Itcontrols the chassis’

tendencyto move sideways in relationto

the rear axle whenoff-road and when

cornering on-road, especially when the

vehicle is heavily loaded.

It’s a simple mechanismformedof two

armsconnectedby bushesto brackets

boltedat each sideof the chassis.The

two arms runback and are bolted

toge ther (forming the‘A’ shape) through

the fulcrum bracket which houses the

ball joint which, inturn, connectsto a

bracket on the axlecasing.

The ball joint provides a positivefi xing,

while allowingfor axle tilt inrelationto the

chassis whencornering and on undulating

A-frame ball joint replacement

EdEvans explains why it’s important to keep a check onthe

A-frame ball joint, why it’s there, and how to replaceit

terrain.The A-frame arms pivot on their

forward mounting bushesto allow the axle

to rise andfall vertically inrelationto the

chassis, with theball joint accommodating

the change in angle between the arms and

the axle.

Fore and aft movement between the

chassis andrear axle is alsocontrolled by

the trailing arms that locate the axleto the

chassis. If the bushes on the trailing arms

are worn, they allow the axleto marginally

move out of alignment when acceleration

torque is applied.This causes a slightrear-

wheel-steeringeffect which isn’t noticed

by the driver until the clutch is pressed for

a gear change. At that point, the torque

is suddenly disconnected, allowing the

axle to straighten, and the driverfeels the

steeringtwitch.

A very worn A-frame arm mounting

bushcan ha ve a similareffect but, unlike

A-frame

Trailing arm

A-frame

ball joint

Fulcrum

bracket

MONTHLYTECHNICAL

Projects, repairs, modifi cations and advice guide

the trailing arm bushes, they’ re re latively

unstr essed and aren’t an ongoing problem.

It’s the ball joint thattakes mo st of the

load in theA-frame and, because it’s

mounted centrally, aworn ball joint doesn’t

produce anysteeringeffects. But it does

knock,especially on undulating ground,

and sometimesat the pointof applying

brak es or ac celeration. MoT inspectorsgo

for theball joint. They don’t like looseness

in the joint, nor do they like splits in the

rubbergaitor that protects the joint from

external grit andwater.

The ball joint on the Ninety shown here

was fi ne, but thegaitor was split, and that

would have meant an MoTfail. Whatever

the issue,fi tting a new joint assembly

complete with fulcrum bracket (except on

vehicles with aself-le veller) and newgaitor

is always the answer. Here’s how it’s done.