Oh so many questions and so little time ;-) * Dampers (hydraulic) provide a resisting force related to velocity and direction, but it is only really trick ones on some of the latest luxury/sports cars & military vehicles that also relate damping to deflection - work on going. * One significant deflection related effect one can achieve to advantage with damping at the front is to ensure that the top rubbers on the front dampers are not over tightened. Only tighten the top nut sufficiently so that one can still turn the top steel washer by hand - use a Nylock nuts or double nuts. That way when the damper is seeing high velocities, causing it to resist and thus stiffen over small deflections on road surface irregularities, the top rubbers can deflect rather than the damper resisting. This allows the tyre to follow the rough road surface for grip and at the same time achieve good ride comfort. * Dampers can be and are of course tuned to provide optimal damping for each vehicle considering mass, ride, handling, friction in the suspension etc. * Indeed monotube dampers (eg Bilstein & others) can be tuned to give the optimal force/velocity characterisitc for ride & handling in one application that is very difficult to achieve with adjustable dampers where the emphasis is naturally on making the damper more suitable for a wide range of applications. * There is so much friction/stiction in the sliding pillar/hub front suspension (even with good pins and bushes) that the amount of hydraulic damping required by the front damper will be less than expected compared to a sports car of similar mass with suspension with less friction, such as ball jointed wishbones. However it is possible, not easy, to match the damping required from the tele damper with the friction in the system to give what damping characteristic is required for good ride and handling. * IMO There is no real reason why there can not be different makes and types of damper front and rear. After all the rear leaf springs, if well lubricated, have less friction than the front so damping levels will be very different anyway. Also what one feels through the seat in terms of vertical bumps is mainly from the rear suspension (you sit close to the rear axle). Getting the front suspension to work majors on keeping the front tyres following the road for good grip and control but also to stop the pitching (like a nodding dog as the nose bobs up and down) that causes the uncomfortable pitching as the seat back slaps you in the back. * Rear dampers. Due to the significant range of weights on the rear suspension IMO I would still go for an adjustable damper (in bump & rebound) on the rear to cope equally well with one lightweight occupant as well as two larger people with lots of luggage, damping needing to be adjusted to suit. Maybe we need a rear damper that has extremes of damping to meet the lightest and heaviest weaights and no more than that? I am not yet convinced that the available Bilstein rear dampers are optimised for ride as well as handling - more work needed on the ride side of things.
Regards PJB.
PS. Gambalunga you say:- "..I have had several discussions and some correspondence with the designer of the system", well you (and others) have now had contact with his test driver and consultant/development engineer ;-)
Thank you very much for all the detailed information, PJB and Gambaluga.
Now I start to get a clue about the shocks. It is easy to understand the principles of the raising spring rates but it is important to see the relevance of the matching shocks. I thought (but I was unsure about it) it makes sense not to change the back dampers as well as a must - especially if they are already tuned to the back leaf springs.
By chance my tin car is a W212 Merc. which has very good suspension and ride feel. May be that the following info is at least partly the reason why (I think it was one of the fírst cars equipped with it - paragraphs by autoworld.com) and it sounds similar:
The W212 comes standard with adaptive shock absorbers [passive direct controlled], which vary their damping rates based on driving conditions. In normal highway cruising mode, the shocks soften – allowing the car to absorb road undulations without troubling the occupants. During high-speed cornering or sudden directional changes, the shocks then firm up to give improved handling characteristics.
Thanks very much for that clear explanation. I can't wait to get hold of a set.
In my observation the front suspension on the Morgan does effect the comfort of the ride, as you pointed out, with that kick in the back. The harshness of the rear suspension is felt more in the seat of the pants and in the noise of the sudden jolt as the rear wheels hit the bump or pot hole.
I am planing on eventually fitting 195/65 R15 tyres which have 10 mm higher side walls and then get the rear springs sorted. I need a set of 4 leaf springs that will give me the ride hight of the 5 leaf springs less 10 mm to maintain the ride hight I need with the higher profile tyres. I know I can adjust it with a spacer but I would hope to avoid that if possible.
Before you all rush off to get funny springs and wobbly wishbones please consider the following. Apologies it’s a bit long
First the positive bit. Theoretically Morgan suspension design is as near as perfect, short of anti gravity, you can get. Two important points. The track remains pretty well consistent throughout the suspension travel and is certainly better than wishbone suspension where the radiusing effect of the arms has to be compensated by flexing of the tire sidewall. Secondly it has potentially the lowest unsprung weight of any suspension system since the only thing that moves is the wheel and the stub axel assembly. Something important in a light car where the ratio of sprung to unsprung weight determines how well the wheels stay stuck to the road. It also has an elegant elemental simplicity about it. It says what it does and how it does it and this philosophy explains why the car is the way that it is. So how come in reality it performs as badly as it does?
First lets define badly. Tootling along a gently undulating road is fine. Hitting anything like a pothole, or worse still a patch of seriously unlevel road the impression is that the suspension has a temporary nervous breakdown. Do it on a hard corner it is disquieting to the extent that what you gain in performance and general roadholding you loose because of the not unreasonably fear that the suspension will suddenly stop doing what it is supposed to be doing. Its quaint, entertaining and I suppose only mildly dangerous but it does beg the question why? And I don’t think this has anything to do with the legendary hardness of the suspension or inadequate shock absorbers. So is this something inherent to the design and is their anything more that could be done to improve it?
One obvious observation is that there is absolutely no compliance built into the system. By this I mean things like the rubber bushing found on the inboard end of suspension links, which provide some sort of insulation to the mechanical components from sudden shocks. In the Morgan everything is metal on metal so perhaps it is not surprising that the impression is that under certain conditions the suspension appears to momentarily freeze. So is this really what is happening and if so why? If the suspension bushes were evenly loaded nothing would be a problem, but of course they are not. As with any kingpin the fact that the wheel is offset creates a strong angular load on the bushes which is not too much of a problem for a joint that only has to turn, but is perhaps a more serious problem where the thing has to slide up and down as well. And to visualize what I think might be happening we have to imagine a Morgan suspension with a single badly fitting bush. The stub axel assembly with the wheel in contact with the road is being twisted relative to the fixed kingpin so in our single badly fitting bush it is apparent that the entire load of the car is bearing on the outside top corner and the inside bottom corner of the bush. A situation that would clearly jamb as what should be a load distributed over the face of the bush is actually bearing on a very small surface represented by the corners of the bush thus creating very high frictional forces. Think about the crude ratcheting arrangement on the plunger of your grease gun or a cheap mastic gun. One might reason that if the bushes were a good fit, that their were two bushes a reasonable distance apart as they are and lubricated with copious quantities of thick grease this effect would be fairly minimal and the system would work, which of course it does. However this jamming effect is always to a small degree going to be there and crucially the friction is going to be greater or lesser according to what the car is actually doing. Subject to a sharp shock the first response of the suspension is for the increased angular load to cause the bushes to dig into the pillar, potentially breaking down the grease film and increasing the friction. One would also have to reason that the sideways frictional forces on the bushes must vary quite dramatically when subject to inertia loads when breaking or cornering. For example in heavy cornering the inertia forces on the outside wheel at some point balance out the angular forces supporting the car thus dramatically reducing the friction. But on the inside wheel the frictional forces are proportionally increased. And this perhaps explains why the performance of the suspension varies quite dramatically according to road conditions and the lateral loads to which it is subjected. And this is not good. In practice this means is you can’t confidently drive the thing to its limits because you are never entirely sure what those limits are. The best you can say is that they are variable. And variable can also mean unpredictable. Or as Top Gear put it; you point the thing into a corner and see what happens. So is their anything more that can be rung from this theoretically brilliant, but I would suggest fundamentally flawed system?
One could argue that these changes in frictional loading in response to varying lateral loads are inherent to any suspension system but are perhaps have a more significant effect in the Morgan design because of the larger diameter of the kingpin and the fact that the bushes have to do two things; that is both turn and slide. And this explains why lubrication is such a critical issue. My instinctive feeling is that the lack of compliance in the system may also be part of the problem. If for example the bushes were fitted in slightly flexible mountings, like a silentblock bush rather than pressed rigidly into the stub axel this might have the effect of cushioning them from sudden shocks, but perhaps more importantly keeping the bush naturally aligned with the axis of the kingpin so that the frictional forces are more evenly distributed across the entire face of the bush. However, regardless of whether or not this would have any useful effect the system obviously depends on very effective lubrication and the more effective it is the more it will mitigate, but not eliminate, the effects of these variable frictional forces. The total loss lubrication system. You pump in the grease and nature takes it out again is alright up to a point except that its performance depends on how enthusiastically and regularly it is serviced and there is of course the problem of having an grease sodden lump only inches from a brake disk which must never be contaminated. A design issue that you could claim was suicidally negligent.
The obvious solution; that is effective seals to the bushes to keep lubricant in and dirt out is I suspect in practice rather difficult to achieve. The problem being the grease. Grease lubricates by sticking to the surface of things and unlike oil isn’t very mobile. So to devise a seal which will hold the grease in means the seal has to wipe the grease off the surface of the kingpin and then replenishing it afterwards, which it clearly isn’t going to do. So in an ideal world the system should be lubricated with oil not grease. People who manufacture things like Mc Pherson struts or rams for earth movers don’t seem to find it too difficult to devise effective seals to keep fluids in and dirt out so you could safely assume that if the lubrication reservoir between the bushes was filled with oil rather than grease, effective oil seals should keep it largely where its supposed to be. So would oil mobile enough to be constantly wiped on and off the kingpin be heavy enough to provide effective lubrication of the bushes, given that we suspect the variable loadings are rather high? Probably not, otherwise someone would have tried it. Which leads to the fairly obvious conclusion that what the system really needs, and deserves, is its own independent pressurized lubrication system.
Relatively thin oil is pressurized by a small hydraulic pump and fed down a hollow kingpin exiting through cross drillings into the stub axel lubrication reservoir between the bushes. Its forced under pressure past the bushes and collected in a chamber between the bush and oil seal and returned at low pressure via a flexible pipe to a remote reservoir that feeds the pump. Which sounds complicated, but given the fact that the lubrication system is now virtually maintenance free and in conjunction with modern oil seals and hard chrome kingpins ought to last as long as any other competitive system. Doesn’t involve the re design of any major components, could probably be reto fitted and ought to work. Or at least guarantee that the system was working as well as it can to mitigate issues that I have argued are inherent to the design. Crucially the handling ought to be more consistent and the advantages of the system; constant geometry and low unsprung weight can be properly exploited. Anything else is down to spring rates and damping which is a question of application or personal preference.
And yes. If it doesn’t have Morgan suspension I’m afraid it isn’t a Morgan
All good points there, however may I add: 1. It is suggested by the author that: "The track remains pretty well consistent throughout the suspension..", er not really, double wishbone suspension can maintain track with good geometry. Tried bouncing the front of a Morgan, seems very stiff? That is (partly) because the king pins are not parallel, they lean in at the top. So the track changes in bounce (along with toe angle), thus your bounce stiffness (car stationary) is being added to significantly by the tyre sidewall stiffness. So ever tried placing one front tyre on a 'TrakRite' the drive-over toe angle checker - all of a sudden the front of the car can be bounced by hand as one tyre is now able to move sides in bounce! Try it. 2. Any excessive bump damping from the damper also twists the hub increasing load on the bushes. So run less bump damping and more spring rate increase to limit bump stop impacts. 3. There are plenty of 1.25 x 1 inch x 3mm lip seals around, costs £2.00 each, easy to insert under the crucial lower bush and even the top bush. I orientate mine to keep much out. 4. With main spring rates around 100 lb/inch and low bump damping the hub really does move freely on the kingpin over small and big bumps - fact. 5. Much of the apparent high front suspension bump stiffness many owners (of older Morgans) feel on the road is due to the fact that their rebound springs are still compressed at static ride height. Thus the initial spring rate (in bump & rebound) is around 125 lb/inch [main spring] + 275 lb/inch [rebound spring] = 400 lb/inch. That rate is so high it will appear that the suspension is locked. These are F1 type spring rates! OK different models have different main and rebound rates but the combined rates are all too high - that is why in recent years MMC have moved away from compressed rebounds, except for the +4. Just a few additional thoughts - PJB.
Peter: Some details and a photo of how you fit the seals and keep them in place would be interesting. I have wondered why seals and rubber concertina type boots, such as used on off road motorcycles, are not used on the Morgans.
I fit simple lip seals, better than nothing. OD is 1.25 inch, but is a very tight fit in the hub tube so often the outside of the seal needs to be filed/sanded/skimmed to fit better, buy spares! The 1 inch id is a good fit on the pin though I face the lips outwrds to keep the dirt out and this allows some grease to ooze out past. Here is a link to a UK supplier:- http://simplybearings.co.uk/shop/p32062/...oduct_info.html
Ideally one needs tougher 'scraper seals' in this size, but have not found such yet.
To fit these seals, the bushes need to be be pushed in by around 5mm, so if they were already in place and aligned then they may well missalign, so be warned!
I also use a flexible silicone hose over the rebound spring, such as:- http://www.cbsonline.co.uk/product/38mm__%281_1%7C2%22%29_Silicone_Duct_Hose_SD38 though I rip out the inner spring leaving just the silicone hose.
I run on Vesconite HiLube bushes on hard chrome pins and so far +30,000 miles no wear. The bushes are turned on a lathe to get the correct internal diameter to just slide on the pin, then the outside diameter is rough turned to be slightly loose in the hub tube. Then the bushes are coated in epoxy and then inserted with the pin through the middle of the bushes thus ensuring perfect bush alignement with no need to ream afterwards! Vesco Plastics who manufacture Vesconite HiLube recommend the use of high grade epoxy to secure bushes in place on steel. Works for them and me (so far).
As to why Morgan Motor Co do not fit such is beyond me, they do seem reluctant to change some things.
No photo sorry, as probably not realy needed, but I have yet to find out how to do that, must try harder!
I was hoping to get 100,000 miles plus out of these bushes as others do, so a few years yet - and they were not using seals. I guess I might first try heat to melt the epoxy then pull the bushes out, or put a saw blade through the bush and peel it out - many years ahead I trust. Good question though. PJB
Attached (I hope) photo of the silicone ducting I use as protection for the rebound spring. Also shown of course is the current thrust bearing with seal and a prototype rising rate ring. PJB.
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