Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Softer rebound springs

Peter, one spring pre-loading the other, is just about spot on. I had difficulty seeing the increased spring rates until I thought of things as you have just described

Yes


I’m struggling too. The only way I can see rates accumulating is if the springs were permanently mechanically connected in the system rather than independent. Then if one went into compression and the other in tension the rates would combine?

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’m struggling too. The only way I can see rates accumulating is if the springs were permanently mechanically connected in the system rather than independent. Then if one went into compression and the other in tension the rates would combine? [/quote]

I can see the logic of that Roger, even if it's not the case.
Let's suppose we have a stub axle with equal rate springs on a test rig. If both springs are just at the static unloaded length, but touching the stub - my logic tells me that to move the stub either way - the resistance would be the rate of one spring, not both combined.
So now if we shorten the kingpin so that both springs are part compressed, and we move the stub, why doesn't the expanding spring assist in moving the stub against the compressing spring? Obviously the stub wouldn't move freely so clearly the rate of one spring doesn't overcome the rate of the other, but how it can be a combination is the thing which I just can't compute. I need a test rig.............

If the srings are part compressed they work in parallel in the Mog configuration. Best is, the lower spring just touches the hub without compression, and the upper srings makes the job, so the lower spring does work only on rebound or against body roll.

Still stuck there too. I can see how the two springs in parallel add their rates to impose a combined compressive force onto the hub, but that’s not the same force that is required to then move the suspension. Is it?

Do enjoy the wear the bare tail will induce!

If you want a softer / shorter spring or what ever get one a full one properly made

"Hooke's Law" Read Peter
Ballard's explanation. It is not intuitive!

We've linked to this before but here's a reminder:

Morgan front suspension in action

Obviously we don't know the spec of the springs but it's interesting to see how much time the stub is not touching the rebound spring.

Thanks for posting that link, Dave.

As you say, in the film the rebound spring does seem to spend a lot of the time not touching the hub at all, and even when static there seems to be minimal compression of the spring. I know that on mine the rebound spring was under considerable compression when static, (so much so that it wasn’t possible to turn the spring by hand at all) which led me to believe that things could be improved by reducing its length so allowing the main spring to expand and lose some of its pre-loading, and also reducing the pressure on the steering bearing.

I didn’t want to be too drastic in my actions, so I settled on taking 20mm off the springs with careful use of an angle grinder. With bit of work I was able to get a pretty good level finish to the cut, and with the spring exerting considerably less force than before I’m reasonably confident that no damage will be caused to its mating surface.
The rebound springs can now be turned by hand when static (but only just), so I’m happy that the 20mm taken off is about right. My thoughts are that any more taken off would have left the hub ‘floating’, and any less probably wouldn’t have made that much difference.

Theory is all well and good, but I like to try the practical approach. If it works – fine. If it doesn’t - OK, let’s try something else. For me, this relatively simple (and free!) modification has softened the ride, given increased suspension travel, lightened and improved the feel of the steering, and increased the ground clearance by 20mm. The car still handles very well, and personally I can’t really notice any difference in body roll, but that maybe something to do with my driving style. If I was to try hurtling around a track sometime, then maybe I’d think differently. All I can say is that it’s improved things no-end as far as I’m concerned, so I’m a happy bunny!