Talk Morgan Forums Community The Malvern Arms Rear Suspension . 2006 +4

Peter, interesting writeup, thanks for taking the time to do it

‘for a four seater as they are heavier at the rear and they often/should have thinner (1/4" instead of 1") rebound rubbers under the axle to give greater ride height and importantly for the four seaters also have a closed cell foam elastomeric 'spring aid' like a long soft bump stop but with little hysteric damping on the special rear dampers. These are absolutely vital on a four seater to carry the load of the rear passengers’

Does anyone have a pic of the rebound rubber location on a 4 seater?

By spring aids I presume you mean the Bump Stops fitted to the top of the rear dampers?

Thanks
Will

Very interesting write up Peter, thanks for taking the time to explain in such detail.

Will, you have two questions:

1. The rebound rubber on both two and four seaters is directly under the axle screwed to the chassis. The chassis has a curved dropped section directly under the axle, this is to allow more rebound travel. If you look between the axle and the chassis you will see/feel the rebound rubber. I will try to find a photo and get that loaded.

2. Spring aids and bump stops are quite different, made from different materials to do different things.
A bump stop is designed to take occasional big loads to limit suspension travel in bump and is a material with a lot of damping so as to slow the axle's upward motion. If the damper has 4" of travel, so 3" in bump and 1" in rebound then the bump stop will be around 1" long. It will be maybe 10 times stiffer than the spring and solid with no voids in the material.
A 'spring aid' is designed to take load much of the time. It is a closed cell foam, the gas in the cells are there to give some of the spring effect. It has very little damping as the damping effect should be provided by the damper! It is a spring and maybe a similar rate to the coil or leaf spring it is intended to stiffen. If the damper has 4" of travel, so 3" in bump and 1" in rebound the 'spring aid' may well be 2.5" long! So only 1/2" to 1" of damper rod exposed. A 'Spring aid' is very progressive, so a soft initial rate. You will see 'spring aids' on the SUPLEX front suspension units on the M3W and on the Bilstein dampers on the last of the 4 seaters. Photo to follow.

Cheers Peter. SSL. (Seems much of what I wrote on leaf springs was appreciated, pleased by that)

Some photos. hope this works!



Cheers Peter.

Many thanks for the pics. Yes the car has the Bilsten 4 seater damper fitted as per the picture, but there is no gap between the spring aid and the damper body when the car is sitting on the ground.

Yes it has a rebound rubber but it is about 1’ think rather than 1/4, what impact would making it thinner have? Would that lower the axle on the chassis and give you more clearance?

Many thanks for your help.
Will

What is the top damper in the pic it looks like it has a adjustable spring aide?

Will. as requested.

If the white spring aid is touching the damper body unladen, then the leaf springs have sagged or two seater springs have been fitted instead of the four seater springs that have more camber. Check the gap between the axle and the rebound rubber, if ~30mm then the springs have sagged.

If the rebound rubber is reduced from 1" to 1/4" then care must be taken with the proximity of the ends of the U bolts with the chassis. For a while the Morgan factory drilled holes in the chassis in its most highly stressed location to allow the ends of the U bolts to pass through the chassis at full droop. If you want more bump travel on a two seater then indeed fit springs with more camber and reduce the thickness of the rebound rubber, but beware of the U bolt to chassis issue. It is a good estimation that if you add 1" to the leaf spring camber when unloaded, so sitting on the ground having been bounced a few times, then the ride height will increase by 1".

The top photo is of a Quantum double adjustable highly gas pressurised monotube full race damper on Henry Williams' 4/4 race car, at around £500+ per corner. Car goes quite well I believe. I set up the suspension on that car a few years ago now. The car is at lowest allowed ride height and we actually use a long softish (technical term) bump stop with little clearance before it contacts. I did not have a photo of another exposed bump stop, as mostly they are shrouded. We indeed made an adjustable top mount for the damper top eye that can be rotated with a spiral of holes so that the bumpstop clearance to the damper body can be adjusted to change the rear spring rate progression. We then matched the rear spring rate progression with the front spring rate progression that was achieved with the RS RateRiser spring on the kingpin above the slider. We also used a very progressive 75mm bump stop under the axle to control rebound. Thus the under/over steer balance did not significantly change however hard the car was cornered, thus Henry could control yaw with the throttle. First year out he drove round the outside of the Plus8s on the corners, oh we did enjoy that!

ASIDE - many AVO dampers have no bumpstops as std and so the upward motion of the axle is achieved by the top of the diff' hitting the parcel shelf or the nose of the diff hitting the damper hoop on the later cars, neither is clever. Just fit bump stops on the damper rods. The front and rear adjustable SPAX dampers that SSL sell through Morgan dealers and other Morgan specialists do have bumpstops. Sorry if that sounds a bit commercial.

Cheers Peter. SSL.