Talk Morgan Forums Morgan Sports Cars Classic Morgans (pre-CX) Air spring suspension on a plus4

I would tend to agree Julian upto a point, the parlous state of UK roads today, don't help the enjoyment of the trad. Had I tried for the first time a trad on today's road,s rather then the roads of 40 years ago, I doubt whether I would have bought one.

The gulf has also widen considerably between contemporaneous sports cars and Morgans over the intervening years., the likes of MG and Triumphs were often just as basic and crude as the Morgan was back then. In fact I thought my Ford engined 5 speed CVH was an improvement over my MG Midget, I kept for high days etc..Don't think I could say the same with a MX5..........and on the right occasion any open topped car can be fun.....my CX feels more like a go cart than any of my Trads by comparison, maybe the extra torque and slightly greasy roads adds that bit more spice into the equation.

As part of the process of evaluating Monty's rear suspension I did look at air suspension myself, but I rejected it on the grounds of complexity a reliability. While the ride height adjustment would be useful, if you did want to deploy that benefit on the move and use it as a lift kit to deal with speed bumps etc, you'd need to include an onboard compressor adding further complexity.

Compresors are also very noisy things so for me it would certainly become annoying, I looked at kits for big heavy Harley Davidsons both precharged and with a tank & compressor, precharged definitely seemed the best option but having read/watched a tonn of reviews it became clear you need to accept all air suspension loses pressure over time, and as the air replaces the spring not the damper element there will always be a requirement to pump it up from time to time.

I firmly believe to find the solution to any engineering challenge one must start with an engineering evaluation of the system, you absolutely can't ever hope to correct an unwanted carachteistic if you haven't first fully understood how the system operates in the first place, and most importantly why it's failing to deliver the desired performance. The blind addition of air suspension, better telescopic dampers, improved leaf springs etc etc without first understaning the fundimental design failings of the Trad rear suspension setup is unlikely to deliver the results we seek.

Taking all this back to basics, the primary objective for any suspension designer is to do everything in his power to reduce unsprung mass, this before moving on to choose the correct spring rate to suspend the body and passengers, but also correctly pairing the spring rate with a damper rate to effectively tame the unsprung mass. A solid axle is huge cast iron lump of unsprung mass that unlike an independantly sprung rear end also includes the super heavy oil filled differential and the crownwheel & pinion too.

All this unsprung mass will always conspire against Trad owners, however, let's not lose seight of the fact that a solid axle on leaf springs is as basic and well understood as rear suspension gets, there's also no arguing despide all it's failings this ancient and crude setup can actually be made to work reasonably well. Despite all this, Morgan's execution of it was particularly bad with the issues as I see them being many, fundimentally on a Trad you have an extremely light body suspended over a much much heavier rear axle so the ratio between sprung and unsprung mass is the opossite of what often helps to ensure such a crude suspension setup ends up working acceptably.

To bring this to life, cast your mind back to the last time you drove a van on a solid axle with leaf springs, with the van fully loaded it rides fine, but empty it and the ratio between sprung and unsprung mass changes dramatically, the empty van now hops and skips all over the place and delivers very Trad Morgan like ride quality. Ok, I accept that van rear suspension is always going to be a design compromise between laiden and unlaiden weight performance, but my extreme example hopefully helps to ilistrate just how influential the ratio between axle and body weight is. As outlined above, and for fear of repeating myself, before a suspension designer chooses a system, and long before he even looks at spring and damper rates his primary objective is to reduce unsprung mass, this is becase it's super well understood and accepted that reducing unsprung mass aways yeilds the greatest benifits in handling a ride quality.

The second issue on a Trad is the comical lack of rear suspension travel, this is largely a function of the rear axle being placed above the chassis rather than below it as is common practice and for very good reason. I believe a Trad would benefit from leaf springs on the lighter side combined with extremely firm damping, I also belive the unusal ratio between sprung and unsprung weight combined with the heavy falling axle being assisted by gravity means the dampers would greatly benefit from a considerably firmer rebound to compression ratio. Sadly, even with an optimal spring rate and the perfect damper rebound to compression ratio, the minimal available travel conspires against us because because the poor dampers have very little time in motion to do their job effectively.

Morgan then made the situation worse when they replaced the Armstrong lever arm dampers with more modern telescopic dampers, an idea that has merrit but not if you incline the telescopic dampers and set their pivot points 90 out of orientation to the natural movement of the axle, as dictated by the flattening and subsiquent lenthening of the leaf springs and the compensating swing shackles.

The consiquence of all these design compromises combined with a few schoolboy geometry errors from the Morgan Motor Company means no matter how well chosen your spring rate is, and no matter how well considered your damper rates are, you will never achieve truly good ride quality in a Trad Morgan compared with other vehicles fitted with a solid axle on leaf spring, a suspension system that isn't exactly known to deliver great ride quality even when executed well!

However, that's not to say we can't make it operate a lot better than Morgan did with their poorly mounted cheapo dampers and terrible quality (likely never tempered) sourced from India leaf springs, etc etc ect.

For example:

1. While you can't easily and cheaply add the ideal Watts linkage and A frame arrangement, you can fit a Panhard rod for a modest outlay that is still extremely effective at limiting latteral axle movement, and in my experience it exhibitd none of Panhard rod downsides on a Trad by virtue of our rear suspension having such limited travel in the first place, a Panhard rod is therefore somewhat of a no brainer upgrade for us all.

2. While you can't make the axle lighter, you can rotate the dampers by 90 degrees so they at least operate in harmony with, rather than fighting the natural swing of the axle. When doing this you can also replace Morgan's feeble toy shop dampers with something beefier and of far superior quality from the likes of Bilstien.

3. You can't easily and cheaply replace the leaf springs with coils, but you can fit a set of very lightly sprung coilovers in addition to better quality leaf springs with a slightly lighter spring rate like those from BCC, and pair them with a firm damper rebound setting to help tame that heavy falling axle. You could also fit a set of Roger's spring assisters that cleverly give our crude leaf springs a more sophisticated rising rate effect.

4. You can't meaningfully increase the rear suspension travel, but you can set the axle correctly to make the most of what is available, and share it out between conpression and rebound travel in the optimal ratio. You can also nibble away at the inner arches and fit Triumph TR3 rebound bump stops to liberate a small amount of additional travel just waiting to be released.

5. Ultimately you can't dramatically improve ride quality, but you can fit a set of new and in-date higher profile tyres with a softer sidewall, modern tyres are fantastic in many ways but they are also designed for modern cars that are significantly heavier than your Trad Morgan. However, choose those modern tyres that are desined to deliver fuel economy and you'll find they'll come with far softer and more Morgan friendly sidewalls, now set your typre pressures correctly and enjoy the benefits.

I'm still part way through implementing all the above, small incrimental improvements that are already proving their worth indiviually, and should all add up to something really meaningfull in the end. However, I'm a realist so while there are many improvements to be had for a reasonable investment, a miracle change is not on my list of expectations.

Without wishing to sound defeatist, as Julian quite rightly suggests we are well advised to accept our rear suspension for what it is, and avoid kidding ourselves into thinking it will ever deliver modern car levels of suspension sophisticstion and ride quality.

What I changed was removing the lowering blocks and half of the sandwich stop rubber on the upper side of the axle for the suspension travel. Since then, the axle has never bottomed out and has sufficient suspension travel. This was only possible because the springs sag a little, but I left them as they were and this way the rear is not too high. The sagging came to a stop and everything is perfect for my taste and more I do not need to be happy with my 4/4.

Montegue,


Cant disagree with your overall approach. However it becomes more interesting when you try to sort out the rear suspension of a four seater, which can have additional 2 bodies weight well past the rear axle from time to time. I never had a problem carrying 4 people in my Kent 4 seater with lever arms (no suspension adjustment necessary), but certainly my Roadster 4 seater couldn't cope well with just 2 people. Even benefitting from rear adjustable suspension, it bottomed out on undulating country ;lanes 2 up, as well as the massive axle tramp the car suffered from, just too much power for the chassis and rear suspension setup.

The thought of and not wanting to have to get under the car,to adjust the rear suspension setting from 2 to 4 people, usually in decent clothes, when turning up at friends. who then understandably all want to jump in a go for a ride. Maybe wishful thinking on my part, but just pressing a switch to change the adjustable air suspension setting for when I wanted to carry rear passengers, (with the right orientation of the suspension units,) an air suspension would make life much simpler to live with the extra variable of a rear load.


Just shows how not everything Morgan does improves the cars over the years, my Kent and CVH Morgans whilst not sophisticated handled uneven road surfaces and sleeping police men (greater ground clearance) with much more ease than current trads.

Agreed John

Clearly you're potentially adding considerable weight in a four seater when you take on two rear seat passengers, so I can 100% see why air suspension would be advantagous in that situation.

I also agree than Morgan's attempt to replace lever arm dampers with telescopic dampers was very poorly executed, so much so that the suposed modification may well have delivered a suspension sytem that actually performed worse, not better, than the original arrangement.

Happy New year.

Dave.

Well, my springs, which sagged a little after only three years but then fortunately stopped, were still from Peter Mulberry. They were the 4-seater springs. In my opinion, they were and are not too hard at all, but actually just right for the little 4/4.