Axle Location

 CLASSIC MORGAN REAR AXLE LOCATION

The rear suspension of the classic Morgan is by semi-eliptic leaf spring. This has worked well for many years
but as power output (torque), speed and cornering forces have increased it has become less able to cope.There are three problem areas:


1)Spring wind up under acceleration.

                                                           }both of which can give rise to axle tramp.

2)Spring wind up under braking.

3)Sideways deflection which is, in the main, the give in the spring eye and shackle bushes.

 

To avoid having to redesign the entire suspension all that is needed are restraint bars which prevent 1, 2 & 3. The conventional
answer is to use fore and aft "anti-tramp" bars for 1 & 2 and a panhard rod for 3.

The "anti-tramp" bars need, ideally, to form a parallelogram, when viewed from the side, between the front spring eye and the centre of the axle thus allowing the axle to rise and fall without any spring wind-up but allowing sufficient axial rotation such that the axle is not disturbed by body roll. Because the shackles are at the rear it is normal to run these bars forward to the cross member which supports the front spring eyes.

The panhard rod is a device which is connected to the road spring at one side and the chassis on the opposite side. This does control sideways movement but as the axle rises and falls its effective length changes, putting a strain on the spring and shackle bushes. It is also fairly heavy.

A Watts linkage is more accurate and consists of a vertical link, swivelling at its centre which is usually mounted on the back of the differential casing,on a strengthened rear cover, with a rod from the top of the link to the chassis at one side and a second parallel  rod from the bottom of the link to the chassis on the other side. This allows the axle to rise and fall and twist around the fore/aft axis but resists any sideways movement.

It is, however, possible to overcome all these problems with a simple and light device called an "A frame". As the name suggests this consists of a pair of rods which, when viewed from above, form a triangle between the chassis and the axle. This is arranged, like the"anti-tramp" bars, to also form a parallelogram when viewed from the side between the front spring eyes and the centre of the axle.

For convenience we fit the "A frame" below the axle. This is a system that we have used for many years on our successful racing Morgans and are now fitting to road cars.