Much of the excellent handling characteristics of an Imp can be attributed to the good location provided to the rear wheels by these wishbones, compared with the leaf springs of trailing arms of its rivals.
This excellent, if rather expensive solution was arrived at after the design team was involved in a serious accident whilst taking a bend at 30mph in a swing axle Corvair (they were evaluating).
These wishbones are generally sturdy and trouble free units unless suffering from accident damage or corrosion.
Having basic front suspension (swinging arms) but a superior rear suspension (trailing arms) fairly neutralizes the usual 'tail-happy' handling of a rear-engined car. The swing-axle front suspension gives a high roll centre, which, in conjunction with a low roll centre at the rear, removes a lot of the weight-transfer loads from the rear wheels when cornering.
The problem with cars with the engine behind the compartment is often that of a heavy tail-end, causing oversteer on corners (that is: the heavy tail flies out as you drive round). This was very evident in the VW Beetle with it's swing axle rear suspension, which encouraged the back wheels to tuck in and under as the recalcitrant tail of the thing swung outwards. The Imp's light engine, in conjunction with trailing-arm rear suspension means that this potentially dangerous oversteer characteristic is not present.
The Imp's rear trailing arms were developed by Harry White and a team of chassis engineers.
The handling of the small Hillmans - even in standard form - became legendary.
Quoting from "Apex : The inside story of the Hillman Imp" by David and Peter Henshaw. They interviewed Tim Fry, who demonstrated the Imp to a bloke from Chrysler, just before the take over in 1967:
And the silly American said to me, just as we were coming up to this roundabout, 'Do these things understeer or oversteer?'. And I said, 'Well, I'll show you on this roundabout'.
'You can make it understeer like this, (and we went round the first roundabout), 'or you can make it oversteer like this.' And he was completely silent after that.
Two types of front suspension are standard:
|Imps up to mid 1967
(plus all Chamois Coupés)
'High pivot' suspension
The centre of the bolts on which the suspension arms pivot are 0.8" from the top face of their mounting braket
Narrower pivot bushes
(and therefore shorter pivot bolts)
Pronounced positive camber and higher ride (disadvantages)
|Imps after mid 1967
'Low pivot' suspension
The centre of the bolts on which the suspension arms pivot are 1.8" from the top face of their mounting braket
Slight positive camber and a lowered ride height
|Suspension Geometry AutoZine Technical School
Suspension bits of knowledge
The Imp Site