Some more engineering for the rear monoballs
Due to the necessity of using a washer, this may cause some undesirable effects with the geometry of the rear suspension, as using too thick of a washer can change the position of the arms.
I got a hold of some stock M3 arms (as I had foolishly pressed them out of my arms already)
I measured that the tapered face of the rubber joint is 1.5mm more outwards from the centre of the arm than the flat face of the monoball joints. This means if I had simply put a washer on the monoballs, the position of the arm would change. Since we are adding 2 washers, any increase in thickness over the rubber joints would result in the arms moving more inwards towards each other on the knuckle.
The rear suspension on these cars is multi link, and the upper two arms form a virtual pivot that extends beyond the knuckle. This allows you to move the pivot of the suspension to a location where the ball joints simply cant fit, because a knuckle or brake disc is in the way. Moving the upper two arms more inwards will result in the upper pivot point more inboard, and result in more negative camber. This is undesirable for me, since the camber adjustment is usually at its limits trying to achieve a 1 30' (1.5 degrees) camber.
Therefore the ball joints must not be pressed to depth flush like my previous post
, they must be pressed offset slightly (and the opposite direction for L and R). This will allow some space for a washer to fit, while still retaining the centreline of the arm with respect to the knuckle (when compared to the stock rubber bush)
I decided on making the washer 4.5mm thick, and this requires the monoball to be pressed in offset 3mm. This is easy since the chamfer on the monoball is 3mm deep, so visually it is easy to tell that the ball joint in pressed in correctly.
Below is the washer design and a diagram of the upper two arm geometry. It is easy to see that by adding a thicker washer on the mounting face on the knuckle, it would result in the arms being spaced closer together, and therefore move the virtual pivot more inwards.