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Princess suspension is weird and wonderful, utilising spheres that contain gas and fluid under pressure rather than springs and dampers. Unfortunately, these spheres fail and new replacements are not being produced, which means an ever dwindling supply of parts for a component that will, eventually, fail. I hadn't worried about it seriously as a problem until I had a sphere fail and while I've found replacements second hand I have no idea how good they are or how long they'll last.
This got me thinking about alternatives. My gut feeling is that an air bag set up would be the best replacement as it could use off the shelf components making for easy replacement should it fail. It should also allow me to best mimic the soft floaty ride of the Princess that I like so much. Best of all, though, I can control the ride height just like I could in the BX I had.
So how do you go about fitting air suspension to a car that has no suspension struts?
In the simplest terms, the front spheres are located inside the crossmember that runs across the front bulkhead and the rear spheres form part of the trailing arm. I don't know how or where you would attach the necessary dampers that complement the airbags. At least there's bags of space to fit compressors and the pipe work for the suspension.
Cost seems to be £1-2000 for a ready made kit for a specific car, I have no idea what sort of cost it would be for a fully custom set up and no idea whether it would be possible to DIY this sort of thing. Certainly, it's beyond my skill and experience to fit so it's a job to be entrusted to someone else.
Is there any reason an air system would be a bad idea, beyond leaking bags of course? Is there a better system I could utilise to maintain the wafty drive?
Advice welcome, particularly from anyone with experience of building and/or fitting air suspension.
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VIP
South East
Posts: 8,293
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To be brutally honest, if you have no experience or skill to fab up an air system on a car that doesn't have the basic design of suspension to take air, and you're getting someone else to do the work, unless you have a LARGE chequebook, I'd forget the idea.
There'll be so much design and fabrication involved, that someone isn't going to get involved at 'mates rates', as it will be a pretty long and drawn out process, so that means handing it over to an existing specialist shop, and bearing the charges associated with it.
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Might be better to develop a method of fitting Metro / MGF displacers so the idea can benefit all Princess owners. Another thought is if the MG TF changed for displacers to springs could that be the direction to investigate as well.
paul h
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I pondered the same thoughts when I was running Allegros daily. (This year!) To be honest, I fancied ripping out the hydrogas setup altogether and putting on coilovers, which with some bracket fabrication and willpower could be done -- and someone out there on the interwebs has already done it, I believe.
So, (not knowing princess suspension) if it can be sprung, surely it can be airbagged too? All that would happen is the 'bag' units would take place of the displacers and act in the same way. Am I right in thinking, if the 'spheres' are mounted against the bulkhead, that means the front suspension is sprung 'horizontally' a-la rover P6?
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"A Pierburg carb? It would be more economical to replace it with a funnel..."
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A quick google shows that the Princess spheres look very similar, if not the same as the Metro/MGF spheres.
I am going to swap the gas in my MGF for the coilovers fitted to the MGTF. The issue with this for me (and I'm guessing for you) is that the original stut towers wont be strong enough to support a coilover shock. To get around this I have both complete MGTF subframes to swap in, which were redesigned to fit coilovers to.
This may be an option for you and it's probably worth getting a tape measure on a set to see how similar they are to the princess subframes. One thing to bear in mind if you go this way is that the 'TF suspension is quite hard, so it might also be worth looking at a set of GAZ coilovers with the 'soft' option.
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'03 Porsche 996 C2 3.6 - Sort of Retro '84 Porsche 924 - Definitely Retro!
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VIP
South East
Posts: 8,293
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If ^this^ is the case, then you can fit coilovers with strut bags, which makes the whole process muhc easier, although still not cheap. You'll be looking at £800 just for 4 bags.
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I don't expect it to be cheap, I'd like it to be, but I don't expect it to be. Problem is, I really like the Hydragas system but nobody is supplying parts to keep it going when it does eventually fail. I know the front spheres can be swapped for Maxi and I believe MG spheres up front too but apparently there's something about the rear end that means you can't just swap the spheres out even though they look the same, I'm just not sure what that is. Front spheres are almost horizontal, rears are too now I think about it, but the front ones are mounted so the go side to side while the rears run front to back. I presume someone that knows what they're looking at would be able to figure out the strongest mounting points for an alternative suspension system, or even a subframe which is something I'd not considered. If I'm dropping MG subframes on I might as well drop an MG engine in too hadn't I?
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Go to Rayvern Hydraulics, every set up he does is custom any way.
As long as there is some chassis to weld a 6" diameter circular plate and enough free space / suspension tunnel with 6" clearance then air bags can be fitted.
As standard my cube has struts up front and independent spring and strut at back (pretty standard stuff) and were replaced by air strut up front and bag on a plate with standard strut at rear.
It might end up being cheaper than normal setup as fabricating custom air struts is more expensive than just fabricating plates to weld the bags to.
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VIP
South East
Posts: 8,293
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You'd be looking at the fat end of £4k to get Ray to fabricate something for such an unusual existing suspension setup.
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Last Edit: Nov 6, 2013 15:25:02 GMT by VIP
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I'm more concerned with the possibility of this as a suspension option that's more maintenance friendly in the event of failure than I am in the cost. Cost I can deal with later, if I do go this route and I'm expecting it to be fairly high because of the nature of the car and the lack of precedence for it. General consensus appears to be that it can be done, but that I need to do more direct research with the UK companies I think. And to find a place that would be willing and able to make up a system for the car. I have an aversion to pestering companies for quotes if I'm not in a position to pay for what I'm asking about, but I guess I have to get over that in this instance as otherwise I just won't find out. fr€$h&m1nt¥: I'd like to use as many stock components for this as possible, I'd not considered that it may reduce the price of a custom system by doing so. The easier it is to replace components the better, really, because these things do eventually wear out over time.
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HGV's have airbags, they wouldn't if they were not reliable
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Surely you could just replace the old spheres with a bag?
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sweaty palms slip off joystick
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Funnily enough, that was my first thought and what led me down this path. Unfortunately, the sphere is both the spring and the damper in one unit. Even Citroen used separate rams on the BX which essentially has factory hydraulics. So the difficulty becomes not swapping out the spheres for what would be quite small bags but also finding a way of fitting shocks to a car that never had them fitted.
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Rich
Club Retro Rides Member
Posts: 6,250
Club RR Member Number: 160
Member is Online
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How do I get my Princess on Air?Rich
@foxmcintyre
Club Retro Rides Member 160
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Funnily enough, that was my first thought and what led me down this path. Unfortunately, the sphere is both the spring and the damper in one unit. Even Citroen used separate rams on the BX which essentially has factory hydraulics. So the difficulty becomes not swapping out the spheres for what would be quite small bags but also finding a way of fitting shocks to a car that never had them fitted. 4 Xantia rear rams? The units are compact.. Be difficult to regulate the hight and pressure. I'd just stick with the hydrogas displacers, how often are you expecting the system to fail?! Just repair it with the parts you have gleaned from the scrapyard and see how long it lasts. I think contemplating this whole 'swap the suspension' thing is chasing dead ends, whatever you fit I doubt it will rival the original suspension system.
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I see but if you only need to mount a damper then it doesn't need the strength of a shock turret as it isn't supporting the car just controlling the bounce.
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sweaty palms slip off joystick
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rich: Trouble is, the parts are getting older so the longer I have the car the more regular I'm expecting failure. Bear in mind the youngest spheres are going to be 30 years old now and the spare ones I got are older than the ones they will replace. I don't know what mileage or age to expect from spheres, they seem to fail without any real predictability, or just last forever and never cause a problem. Other Princess owners are hoarding spheres which is a reasonable response, but I'd like a better solution to the issue, hence considering suspension alternatives. This may be a dead end yet, I'm also investigating getting spheres repaired to see if that's a more cost effective solution but so far the general consensus is that the spheres are a 'sealed for life' deal and can't really be repaired. But then I often get told things can't be done and find a way of doing it anyway so we shall see.
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Is it a similar set-up to a Landcrab?
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Click picture for more
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Landcrab used the earlier Hydralastic which makes use of compressed fluid and can be a little bouncey and not quite as composed as the later evolution of Hydragas which the Princess uses. It is possible to revert to Hydralastic if I really want to, but it's something of a compromise and while the spheres will work up front, they apparently don't at the back.
Otherwise, the system is laid out almost identically with no separate subframe. It's very elegant, I like it very much. The wishbones operate through a plate that bolts to the chassis member/inner wing and connects to a damper in the sphere at one end with a pressure pipe coming from the other end of the sphere to regulate the pressure on the car's suspension.
The Princess and Landcrab are very similar mechanically and only radically differ in styling, really. That's a really good diagram to explain how the front end works too. I should probably scan in the diagrams from the manual to see if it explains the set up better than I can.
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Rich
Club Retro Rides Member
Posts: 6,250
Club RR Member Number: 160
Member is Online
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How do I get my Princess on Air?Rich
@foxmcintyre
Club Retro Rides Member 160
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rich: Trouble is, the parts are getting older so the longer I have the car the more regular I'm expecting failure. Bear in mind the youngest spheres are going to be 30 years old now and the spare ones I got are older than the ones they will replace. I don't know what mileage or age to expect from spheres, they seem to fail without any real predictability, or just last forever and never cause a problem. Other Princess owners are hoarding spheres which is a reasonable response, but I'd like a better solution to the issue, hence considering suspension alternatives. This may be a dead end yet, I'm also investigating getting spheres repaired to see if that's a more cost effective solution but so far the general consensus is that the spheres are a 'sealed for life' deal and can't really be repaired. But then I often get told things can't be done and find a way of doing it anyway so we shall see. It's a fair response, but Citroen spheres are 'sealed' yet they can be refurbished so the same must go for the hydrogas displacers. The thing is, I'm in the same boat with different parts with the Citroen. I have got a few pipes and hydraulic units but the point is that the struts and rams are the same, unavailable and getting rare but I just don't worry. It's just something I'll deal with as and when, rather than planning for something that may never happen. Get me?
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Rich
Club Retro Rides Member
Posts: 6,250
Club RR Member Number: 160
Member is Online
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How do I get my Princess on Air?Rich
@foxmcintyre
Club Retro Rides Member 160
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Also, it does look like Xantia rear rams could possibly be adapted for the scenario looking at the subframe pics..
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