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Our Independent Rear Suspension (IRS) unit is a complete replacement
for the existing rigid axle, leaf springs, and leaver arm dampers.
The 100mm system is designed to cope with up to 250bhp, and the
108mm system up to 450bhp, and fits around the
existing body, battery boxes, and fuel tank without modifications
being necessary. The installation adds to the rigidity of the cars
shell and reduces the un-sprung weight by 55kilos (overall weight
same as std axle), this, together with softer springs and high
quality dampers, results in a more supple suspension. Unlike the
original system each wheel reacts independently to the change in
road surface so not upsetting the balance of the car, and the
unequal length double wishbones ensure that for hard cornering the
small camber change induced keeps the maximum amount of rubber in
contact with the road.
The system consists of a new sub-frame
that supports the differential, upper and lower tubular wishbones,
coil-over dampers, machined alloy hub carriers, and tie bars to the
spring eyebolt location. Also attached to the sub-frame are the new
stainless steel braided brake pipes and the handbrake cables. All
these parts plus all the necessary polyurethane bushes, and nuts and
bolts make up the basic kit. Shims, in the form of quick-change C
washers, can be fitted between the wishbone pivot yokes and the
sub-frame to make minor adjustments to camber and tracking. The
dampers used are the same spec as our front system, the fabricated
parts are black powder coated, and the aluminium uprights are
anodised.
In addition the differential, drive shafts, hubs,
stub shafts, drive flanges and disc brakes are sourced from the Ford
Sierra or Granada. The Ford half shafts require shortening to retain the
standard track dimension, or we can supply them purpose made, at the correct lengths.
The Ford drive flange can be used for centre-lock wheels with a bolt-on splined
adapter, we supply a new flange with either MGB, C, or RV8 stud pattern for bolt-on
wheels. All these Ford parts can be supplied as new or
reconditioned, or can be sourced second-hand very cheaply. There is
a range of differential ratios available (3.1-3.9 Sierra and 3.3-3.6
Granada). The Sierra unit has a 7” crown wheel and can cope with
engine power up to 250bhp whilst the Granada’s 7.5” will happily
withstand higher output engines. For those with big V8 engine cars
that want to drive them hard, or use for track days or competition,
both diffs can be fitted with the standard Ford viscous coupling
type Limited Slip unit, alternatively a Quaife torque biasing LSD
could be fitted. For vehicles over 250bhp, we recommend the 108mm
IRS system (see below).
Fitting the kit is straightforward, once the
original axle, springs, and dampers are removed, the unit, which can
be pre-built off the car, is raised into position. It is attached to
the original damper mounts (4 bolts); the rear spring front eyebolt
mounts via the tie bars (2 bolts): and the check strap brackets (2
bolts). The stainless brake hoses mate with the existing pipe-work
and dual handbrake cables and their linkage attach to the handbrake
drop link. The rear suspension unit can be supplied fully built
ready for bolting to your car. N.B. A minimum wheel diameter of 15
inches is necessary to provide sufficient clearance.
The
instructions cover setting up both suspension systems, but some
customers may find this a little daunting with all the variables
available to them (ride height, damping rate, spring rate, and
geometry adjustments), in which case we are always available to
discuss and advise from our own, and other customers’, experiences.
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Fully built IRS unit |
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Upright CNC machined
from billet aluminium |
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Drive shafts and
handbrake routing of the IRS system |
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(Click any image to enlarge) |
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108mm Independent Rear Suspension
System:
We recommend using our 108mm system if your vehicle is running
over 250bhp. The Differential Drive Flanges are 108mm in diameter,
as are the stub shafts. This allows for the use of larger, stronger
31.5mm drive shafts, as well as larger, stronger CV joints, in conjunction with 7.5" diff with ATB quaife unit.
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We offer lightweight
HE30 Aluminium (6082T6) bearing carriers for IRS systems, reducing the
unsprung weight of the IRS by 2.0kg compared to the standard steel
Ford version. This makes for a notable and valuable upgrade, as the
lower weight leads to a reduction of inertia, improving the handling
quality. |
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These bearing carriers include high quality bearings fitted. |
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Ford
differential drive flange does not have the same pattern as an
original MG propshaft.
We carry in stock Propshafts to suit MGB rubber bumper using
standard engine mountings and either LT77 or R380 gearboxes. We can supply any
propshaft required, from T9 to T5 and T56 Magnum. Flanges are
available so that you can have your own propshaft made locally if
preferred. | |
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Ford
Differential flange: |
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Small for MGA/MGB: 23.5mm Large
for MGB V8 and RV8: 26.8mm |
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Hoyle Suspension
now offers a complete exhaust system with RV8 style manifolds, with
single or twin box, and large rear box (modifications are required
to the spring hanger, especially on rubber bumper cars).
The main advantage of
the system is that the rear section passes through the IRS,
increasing the ground clearence of the vehicle. It also increase the
aesthetics, as the silencer is much higher, which prevents the
exhaust from looking like it is falling off, which is something many
of our V8 customers have mentioned to us. |
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(Click any image to enlarge) |
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