Important seems to me to understand, that the combined load of both springs in the Morgan front suspension sytem are in parallel...as long as the hub touches both springs. In parallel means they are adding their forces, even if it "looks" like they where in a serial mode, but the hub is in between the to springs...which means parallel.
Then, if one of the springs' forces do not touch the hub any longer, usually the rebound spring, this is leading to a sudden massive loss of spring load in total, with all the consequences.
In this article, Peter Ballard explains the interaction very understandable. Just foward to the section where he describes the difference between prallel and serial loads of springs.
https://sites.google.com/site/morganatica/suspension/main-rebound-spring-interation I concur re thepart about how many springs touch the hub at the same time. Also adding that if both are in tension then they will oppose each other with pre tension pushing against each other. All the videos showing the rebpund springs during road use show the range of motion of the hub, often rising way above the rebound spring. There are also times when the rebound spring appears constantly in compression. It is a shame there is no matching footage of the main upper spring as both need to be viewed to give a clear picture of interaction and how it varies when on smooth, bumpy surfaces and also during cornering.
Without actually checking and going from memory, my main springs are under tension when at rest as I cannot rotate them, unlike the rebounds which can be rotated without much effort.
One thing I notice is when hitting a deep depression in the road(pothole or drain etc) there is a clear thump. I wonder if the rebound spring is then fully compressed and the cross brace/chassis having to absorb the motion. The rebound springs compress a fair bit anyway with the car jacked up so a sudden drop of the wheel in a hole plus the push of the main spring aiding gravity on the wheel will compress the rebound to binding. A case for a bigger pitch in the rebound coils with modified spring rate poundage?
