Saturday, July 24, 2010

McPherson strut suspension

Unlike torsion bar suspension, McPherson strut suspension feeds great stresses into the body shell —namely the flitch panel tops, where the top ends of the struts are located. On such cars, the panelwork around ut top mounting must be very sound.
The McPherson strut comprises a concentric coil siring and damper, combining both springing and damping roles in a simple unit, which is connected to the stub axle via a ball joint. The lower stub axle ball joint connects it to the track control arm which, in turn, Is mounted on a bracket just aft of the frame head and the movement of which is controlled by the anti-roll tabiliser) bar.
To remove the strut, chock the rear wheels, jack up the front of the car and support it on axle stands then remove the road wheels. Undo the stabiliser bar end nut on the track control arm, then remove the stabiliser bar mounting clamp nuts and detach the bar. Split the ball joint at the track control arm/stub axle, and the steering arm/stub axle. Clamp the brake hose and remove the brake pipe from the bracket on the strut.
The strut is held at the top in the flitch panel by three lock nuts; remove these —don't touch the large central nut, because this is keeping the spring compressed—and lower the strut downwards.
Don't even contemplate stripping a McPherson strut unless you have spring clamps as shown in the illustration. The coil spring is under considerable pressure and can do great damage if this pressure is not release slowly and safely. Broken or tired springs and ineffectual dampers may be replaced, but unless you have a spring compressor this work is best entrusted to a professional who, because he will not have to remove and refit the strut to the car, should not charge too much in labour.

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