Alko shockers are colour coded. My `van has been fitted with black ones which are or were the heaviest duty. My caravan is a lightweight, and afaic those shockers look like they`re seized; the result is, no wear on my rubber "suspension". The tyres are the suspension.
Might not seem ideal, but it`s been this way for 25 years and still counting.
Glad you can`t ride in the vans anymore!.
------------- Peripheral people don`t have as much excitement but they sure live longer
Dampers never seize - they are filled with oil and they leak when they are knackered and don't work anymore. The AlkO arrangement is variable apart from colour coding they have three mounting positions on the chassis the center one is the normal setting but if the van is running full or light this can be adjusted for optimum position. To reiterate, all suspensions should be damped,rubber used in compression offers no damping - they will bounce between the lobes with no control and if the resonance is out of phase with the tyre hysteresis - wheel bearings are the first to suffer and tyres are at risk not to mention losing wheels- quite often with many vans.
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Most people simply do not understand how dampers work because they have never been trained in engineering and studied for hours on end then pass examinations giving them qualifications to show they know what they are dealing with. Dampers on vehicle suspensions are often double acting with a much higher resistance on the rebound, this is important to understand since when the wheel hits a bump it is allowed to rise easily with small resistance allowing the "spring" to absorb the shock not the damper, when the spring rebounds it is then the dampers job to slow the rebound. This means it makes no difference to the stiffness of the suspension. You can verify this when you push down on your cars suspension - it will go down easier than it comes back up thus stopping any bounce. The MOT used to test the dampers this way but since it was found the wings of cars were being damaged they now only test by leak examination - any leak and they will fail. More expensive cars now offer variable rate suspension but the same principle applies - it may or may not alter the rise slightly or even the rebound or both it depends what the engineer is trying to achieve. Hope this helps everyone.
interesting comment about MOT testing.. i have seen many a dud damper that isnt leaking so dampers dont get a real test any more it seems..
there used to be an old car enthusiast saying that went..
"springs govern the ride height dampers govern the stiffness"..
crude cheap rubber trailer suspension dosnt behave in the same way that "real" car suspension does though..
caravan suspension is about as basic as it gets.. excessive rebound bounce isnt its problem..
my memory could be faulty here but i think the original 1957 Mini Minor which had rubber suspension did not have any additional shock absorbers fitted.. it didnt need them..
Hi Trog,
I concur with what you say. I have opened up many dampers in my career to see why they fail and how they could be improved. Valves do get weaker and fail sometimes but modern dampers use various ways to build redundancy in, the important bit is the resistance through a small hole that does not change but where it is double acting that uses different rates it is always a valve arrangement. Rubber was used in the BMC 1100 series (Hydro-static) and used hydraulics to transfer energy from front to back to give flatter ride but like the mini it was very hard on the ride. multi link suspensions on cars especially the Peugeot have revolutionized suspensions and handling - could be where caravans are lacking by a country mile. I disagree with your excessive bounce comment. I installed up to 5 cameras when I was developing the DSS and I cringed at the difference with dampers and without. It was like watching an elastic band being plucked, Loss of wheels is the result of this. I can't prove it is the only reason for uncontrolled sway but it is on the list of high risk.
Springs do govern the height but essentially they absorb the shock first - the rebound is the extra energy induced on the rebound that is what they control - some damping is used on the impact to calm the resonance - stops the spring breaking after much use.
i fitted dampers to my single axle coachman Amara (yes it didnt have them already) because it doesn't tow nicely.
i cant discern any improvement for fitting the dampers.
i can appreciate how dampers would improve the towing of a twin axle caravan but the "yaw" (seesaw action) of a long single axle will be there with dampers or not and its the yaw that makes towing unpleasant.
i am sure damping the bounce of the axles is better for the contents of the caravan but in my experience doesnt improve the towing. i think only an extra Axle does that.
------------- First van bailey ranger 550/6
Now the proud owner of a coachman amara
Hi BaileyJake,
The driver of the tow vehicle cannot always feel the effect of wheel bounce on the caravan - you would need to fit cameras or get someone to follow you to see how much bounce is going on and even this may not let you see how much flutter the axle/wheel is experiencing.
Loss of wheel occurs when the wheel gets shaken beyond what it can accept - flexing of the metal that the bolts hold it on with. Ensure you have them balanced as well as other precautions. I don't wish to be rude and not intended for you but I hear this a lot - I have been towing for 20/30 years or not in my experience of ..... You have to be qualified in engineering to KNOW what is going on.
The yaw you experience is quite normal since when any force hits the van is will move sideways even with twin axles - it is a fact of life (physics). How you control this to prevent it becoming uncontrollable is the key to a worry free ride. I have produced a system that covers all current problems and I cannot get any of the industry to even LOOK despite relentless persistent ranting. So it is not just Joe public that lacks knowledge. Differential stability is the only way to prevent uncontrollable sway and Jack knife from starting in the first place- even with some small faults or inappropriate loading.
John, your post wasnt on when I was putting mine on, so I have been reading posts very carefully. It was me that asked the question as this forum was redundant for a while.it was baileyjakes post I was referring to. But yes, after reading yours also, it does make sense.
if reduced wheel bounce is not detectable by the driver then it would account for why i cannot detect any improvement for fitting the dampers. i can imagine why fitting them to a twin axle caravan would improve the ride because, if the caravan is viewed as a simply supported beam, the axles will act as a 'couple' in the middle and the tow hitch as a support at one end. the 2 axles looking from a side elevation with the mass of the caravan acting downward the yawing i refer to is the sea saw action set up when the car hits a bump in the road before the caravan does. with a single axle the caravan pivots about the contact point between the tyres and the road. there is nothing to damp this motion the dampers slow the return of the rubber block bush in the axle but do nothing to damp the 'Yaw' (except the cars rear suspension)so it rocks like a sea saw.
with the twin axle the 2 axles act as a 'couple' the axles are damped and so dissipate the inertia of the yaw as there is actually a mechanical system to resist the yaw.
similarly looking in a plan view the caravan tuns about the centre of the axle (sway) and there is nothing to resist this with the exception of the towing vehicles rear tyres. there is always play in the silent block bush suspension and tyre side walls so this can be detected in the car as sideways movement.
with a twin axle there is again a couple in this case just the friction between the tyres and the road but the dampers cannot help to resist this because they act perpendicular to the sway.
Whoateallthepies, As the driver i could not detect any difference in having fitted the ALKO dampers. (which i think was the original question)
maybe though JohnMW you can help with my towing problem. at 55mph the caravan starts to oscillate as if a natural frequency has been reached. it never gets to an amplitude where i lose control of the car but it does annoy me. if i drive at 60 the oscillation disappears but when slowing down through 55 its back. i have chenged the friction pads in my ALKO stabilizer (incase contaminated) but have not tried towing the caravan at 55 since then. interestingly towing in windy conditions noes not make the problem worse. but it is never the less disconcerting. there may be a problem with my car, i cant detect any play in the suspension joints. and solo there does not seem to be any problem. when its serviced i will get it checked out. i must add i fitted MAD coil spring assisters but did this when i had my last caravan and that towed ok. i was thinking though that the oil viscosity in my cars damapers may not be suitable for the additional stiffness of the MAD assisters.
------------- First van bailey ranger 550/6
Now the proud owner of a coachman amara
my van used to "wag its tail" predictably and noticeably at 55 mph.. it did not get any better at 60 ether..
the tow truck had a drop in ball pin so i had no stabilizer action at all.. i fitted a bulldog blade type stabilizer and some alko shocks..
the two together 100% cured the 55 mph tail wagging.. i can now exceed the legal limit and everything is rock solid..
i like to cruise at 60 mph which is slightly faster than lorry speed.. but sometimes the speed can creep up a little higher before i realize.. 65 mph or so..
i think the bulldog stabilizer played the biggest part in the tail wag cure but the shocks may have helped.. i followed a simple principle.. i did everything i could to produce a stable tow at speeds higher than i need to go..
i still dont think shock absorbers are essential on simple rubber suspension but i dont think they do any harm ether.. he he
if simple rubber suspension has its faults which it does.. they are simple ones.. its too bloody hard has too little travel and it does a poor job of absorbing road shocks.. but its cheap and it kind of works.. he he
Hi Baileyjake,
I think I got your drift on the first Part of your post, how ever putting it simply - Any wheel on any axle needs damping regardless of axle numbers because it affects the individual wheel not necessarily the axle. When we talk about "ride" it is refereed to the level of comfort for those in the vehicle but the other components of ride are the ability to hold the road, steer the vehicle and carry a load safely. However, yaw rates do change with the axle number and also the term "stability" is often misunderstood with the belief that twins are "inherently" more stable. Twins present instability/stability in different ways as I tried to explain in other posts.
I assume your van is single for now. If you have this annoying and worrisome oscillation then you are among the majority of caravan users, I'll try and explain - all machines and vehicles have a natural frequency albeit vibration or resonance etc with caravans the troublesome frequency of oscillations is about that speed and for years authorities and engineers have tried to safeguard the towing of caravans by limiting the speed to 60 mph because non have been able to come up with a method of controlling it permanently. In France the speed limit is 80 mph for combinations under 3.5 tonne - now I think that is a crazy speed to tow a van at,however, I have towed mine at that speed with no effect on the combination just my nerves were shattered doing it. I digress - your combination simply drives up through the period of its natural resonance as you have found out. This is because you do not have any control other than the silly ALKO friction hitch and if you have the ATC it won't let you past the 55 mph - it's just a speed governor which the authorities like, not a control of yaw. If you have found no other faults with your outfit you need a control system like I have developed to improve your issue. I also fit the spring stiffeners - good choice because your car is designed for optimum carriage of people not vans and they reduce pitch which in turn helps your dampers cope better - just check with your insurer to make sure they are happy with that - most are. They may stiffen you ride a little when not towing. I have not experienced the MAD assisters but I believe they are very good. I have a post on " Caravan Stability" on here. Fish tailing is often confused with uncontrolled yaw but it is always going to be be present but only one way - it should return to the center of equilibrium at a steady rate and not go beyond because you are very close to being out of control if it does - be careful.
john
Hi Baileyjake,
I did not want to get to involved in your first part in my last post but I think it needs some clarification. There is a coupling effect that helps reduce yaw in a primary way, however, this is small if you study Simple Harmonic Motion you will note that the pivot in an oscillation is not about the axle center it is about the pivot (ball) so the coupling effect is diminished and reduced to side loads on the two axles. But I commend you for your technical observation. If you can work with calculus you will arrive at more detailed analysis of period rates etc.
Trog I agree totally with your Bulldog leaf accessory it is much better alas still a friction device.