|
11 July 2003 |
These rods have been produced to improve car
stability when cornering and braking and to facilitate easy adjustment of caster
angle. Manufactured from a high-grade material in a much larger diameter than
the standard items they are far less susceptible to bending - both in use and
where poor workshop practice is observed. The most common fault here is jacking
the car up with a trolley jack sitting the cup up against the forward tie-rod
mounting bracket on the front subframe. As the wheel droops, the tie-rod
becomes bound hard up against the jack cup, the sheer force of the un-loading
rubber spring causing the insubstantial standard tie-rod to bend. This
effectively shortens the tie-rod, therefore increasing caster angle.
The standard caster angle quoted by the workshop
manual is 3 degrees +0/-2, so could be anything from 1 to 3 degrees and not
necessarily equal on each side. Caster angle will change when raising or
lowering the car and where adjustable or fixed negative camber bottom arms are
used (increasing camber tends to also increase caster angle). The adjustability
of these tie rods allows accurate and equal setting of the caster angle on both
sides of the car. This is imperative for straight line stability and
minimalising wander/weaving over broken road surfaces - particularly where
13" wheels and limited slip differentials are used. The greater the caster
angle, the more self-centring action will be when accelerating. Increased
caster also improves cornering grip.
Adjustment is achieved by screwing the tie rod
in or out of the threaded block that bolts to the bottom arm. This can be done
without removing the tie rod from it's installed position by slackening the
11/16"AF nut on the front end of the tie rod, undoing the lock nut that
tightens up against the adjuster block then turning the toe rod with a spanner
on the hexagonal shape cut into the tie rod shaft's centre. Shortening the rod
by screwing it into the adjuster block increases caster, lengthening it by
un-screwing it out of the adjuster block decreases caster.
The standard tie rod length is 14.25"
measured from the inner edge of the bottom arm retaining bolt hole to the outer
face of the welded-on washer. One full rotation of the rod adjusts the length
by 1/16", which equates to a little over 1/2 degree. However, the shorter
the tie rod is made, the less amount of alteration is achieved. It is not recommended
to use more than 5.5 degrees of caster, less than 2 degrees will greatly reduce
the steering's self-centring action. Altering caster angle also alters camber
angle - increasing caster angle reduces camber and vice versa. Always start
with the tie rod set at the standard length. Starting with the rod longer can
cause a misleading phenomena known as the 'tea trolley' effect, where the
bottom ball joint (swivel pin) is behind the top one viewed in side elevation.
IMPORTANT NOTE:
The use of very stiff/hard tie rod bushings on
both sides of the subframe bracket is most definitely NOT recommended. Use the
hard bushing on the outside only and a standard rubber bushing on the inner
side. This is to prevent the tie rod end shearing off through over-stressing
when doing the retaining nut up to achieve the required seating of the
retaining washer against the step on the tie rod, and is more than sufficient
to create the increased stability desired when fitting these harder bushings.
It is also imperative the proper, standard fitment cup and flat washers be used
to maintain proper performance of the bushings fitted. The tyre trying to drag
the tie rod back through the subframe mainly creates the instability, therefore
only the outer bushing requires increased resilience. Fitting harder bushings
on both sides does not noticeably improve stability, or cornering performance.
If determined to use harder bushings on both sides of the tie-rod forward
mounting bracket, then it is strongly advisable to cut the one to be fitted to
the inside between the tie-rod welded-on washer and subframe bracket in half
(vertically) to allow the outer nut and washers to achieve their correct
positions without over-stressing the threaded end. Failure to observe all
information here is likely to cause failure at the threaded section.
Useful part numbers:
|
31G1155 |
Standard
rubber tie-rod bushings (need 4 per car) |
|
C-STR627 |
Extremely
stiff 'race' application tie-rod bushings (1 set per car) |
|
C-STR628 |
Performance street
application tie-rod bushings (1 set per car) |
|
21A1091 |
Heavy-duty
adjustable tie-rods only (pair) |
|
ACA9759 |
Cup washer (2
per car) |
|
PWZ207 |
Flat washer
(2 per car) |
|
GHF223 |
Retaining nut
(2 per car) |
|
53K1031 |
Tie-rod to bottom
arm fixing bolt (2 per car) |
|
GHF332 |
Spring washer
- tie-rod to bottom arm fixing bolt (2 per car) |
|
FNZ505 |
Nut - tie-rod
to bottom arm fixing bolt (2 per car) |