Talk Morgan Forums Morgan Sports Cars Classic Morgans (pre-CX) Steering bearings

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My own understanding is that rebound springs were historically shortened as a bodge (as per CBY post) to reduce static pre-load on rebound springs which in turn resulted in the fact based massively high spring rate of having both springs in play. This in turn causing uncomfortably hard suspension but then sagging into corners due to inside main spring compression taking rebound spring out of play and effective spring rate reducing to that of main spring alone. Several owners and at least one magazine test of Plus 8 brought this fact to light many decades ago. Peter Ballard explained it and mentioned that ironically as main springs weakened with age the issue could dissapear. Suggesting the rebound pre-load test is rubbish for an entirely different and less important reason is not a fair comment. Its as relative today for trads as ever.

Exactly correct, a pre-loaded main spring due to a compressed rebound spring gives a massively high initial rate followed by a sudden drop in rate as the rebound spring unloads.

All documented and explained years ago by Peter Ballard, I remember the huge consternation it caused among people who didn't understand the physics behind springs in parallel vs. in series. It was hugely entertaining at the time to read all the eMog posts telling Peter he didn't understand how suspension systems worked!

https://www.lambdapi.co.uk/morganatica/Front_Suspension_Spring_Characteristics_-_Trad_Models

Well CBY is totally correct in his analysis of cutting springs down, take the boy racer with his cut down micro hatch back. It's not an MOT fail for no reason!
To a great extent the rebound spring is just a damper. When in a turn enough to effect G forces which load the outside suspension the spring compression rate of the main spring has no detrimental effect from its ability to compress at the design rate regardless of whether or not the rebound spring remains at full unloaded length or is subjected to a degree of compression itself. Its main functions are to keep the hub carrier in a balanced contact position on the pin whilst allowing the small movements as the hub responds via the wheel to the movement from the road surface. This prevents hub carriers hanging up on the pin as during these smaller movement it has a push pull effect to the carrier.

When/if the suspension is subjected to a sudden and harsh suspension requirement the compression rate applied to the main spring can be large and the distance up the pin the carrier can travel is substantial within the design profile. During this event the carrier will lose all contact with the rebound spring and when returned to its normal position by the return force of the main spring the rebound spring will absorb the shock as the carrier reaches the bottom of it's travel and damp the shock that would otherwise become a metal to metal crash. were it to be a bump stop instead, the return action would be too great for the repeated and constant contact it would receive, and indeed to harsh.

Now here is why they wished to unload the static compression to the rebound spring. and remember these cars originally had no shock absorbers. You can do this in two ways. firstly cut the spring down which increases its compression strength or fit a spring with a greater load rating. What you then want to see is next to no compression or decompression to the rebound spring from either static load position or unloaded and to a great extent this was achieved by spring length, spring load rating and the extended load rating of the main spring. so, if the car now hits a negative obstiacle ie a pot hole most modern cars accelerate the suspension down into the hole only for the wheel to hit the other side and possibly disrupt the stability of the car. This is only offset by the shock absorber fitted as it slows the downward suspension acceleration into the negative obstacle. The sliding pillar system tends to hold its wheel clear without the aid of a shock absorber.