I do love Lornes write ups. He so very nearly listens to what you tell him.
The factory chopped and changed spiting suppliers a few times in the mid 2000’s
I did a great deal of work with Dan White (Suplex, now SSL) in working out the correct rear spring rate needed (and what is actually manufactured) including working with Reading University to design and ascertain whether it was possible to fit a composite rear spring (MMC wouldn’t detail change the chassis to allow it to fit)
Dan White in his then role as UK director of Eibach Springs and supplier to MMC visited a Chinese supplier of leaf springs and rejected an entire production run of springs for being of varying and out of specification quality.
Leaf springs are a b*ugger to design as the friction between the leaves changes depending on use and environment and hence the spring rate also changes
Polishing and deburring the individual leaves and interleaving with a slippery polymer film (as I did for the Peking Paris +4) can make a huge difference, but is hardly ideal for production
The leaf springs fitted to the 4/4 in 2011 were fitted with lowering blocks to obtain the correct ride height, whether they were too stiff, or of the wrong parabolic arc, or just way out of specification I don’t know....
The Mulfab four leaf , four seater springs are identical to the four seater factory springs,and manufactured by the same supplier ( they just happen to be in Coventry) and are probably the best solution to saggingrear springs
However in the original posters case I would be tempted to simply remove the lowering blocks ( this may need new U bolts) and see if the increase in ride height cures the issue
Certainly a cheaper option than new springs
Simon @ SiFab.co.uk
