The Hydragas Problem - seeking a solution

[vulgalour]

As an owner of a car with an important but obsolete component that is prone to failure and made of purest unobtanium I keep revisiting the issue in the vain hope that a solution might present itself.

 

The trouble is the displacers on the Princess.  These are a sealed-for-life unit and unique to the car (Ambassadors have the same, but they're even rarer so don't count) and are not technically a serviceable item.  They don't come up for sale very often and when they do they're often very expensive even for second hand units that aren't known to be good or bad.

 

Here's a diagram.

 

I'm told these units are designed to last about 15 years and are not servicable.  The youngest of them are now at least 30 years old and over that time the nitrogen has usually escaped enough to make the car sink.  If you pump it back up sometimes you get away with it and sometimes it overstresses the internal rubber diaphragms that rupture and render the unit useless.

 

You can get around this to some degree by having a schrader valve fitted to the nitrogen section in place of the closing rivet.  This is expensive, it's normally about £90 a unit (at time of writing) and there's four units to do on the car.  It's not guaranteed to work either, there is a percentage of failure.  However, it is the best current solution as you can reset the gas pressure and relieve the excessive stress on the rubber diaphragm allowing the fluid side to be pumped to the correct pressure.

 

Personally, I'm of the opinion that all the displacers will eventually fail.  Unless someone starts manufacturing new ones - which is highly unlikely - another solution must be found.  It is possible to replace the suspension displacers on the smaller Allegro with coilover suspension, the car has a slightly easier displacer location to accept the modification with upright turrets at the front and modifiable brackets at the back.

 

 

The rear displacers could be replaced with this suspension set up at the back relatively easily but at the front it's more difficult.  The front displacers on the Princess are mounted horizontally across the bulkhead and there's no access to fit the more conventional coilover suspension without cutting away structural metal.  It's probably possible though I can't help thinking it's not the best solution.

 

If I had the engineering knowhow or experience I could modify the car to take an air ride system, a hydraulic system or a coilover set up.  Because I haven't this knowledge or experience I have contacted a few companies and they have all decided to take my enquiries not at all seriously as soon as they've learned what car I'm wanting to modify.

 

 

 

I'd like to future-proof the suspension with something off the shelf that puts comfort ahead of performance (not the usual, I'm aware).  I need to find a company or person that is able and willing to do the work.  I also need to know a cost, which will likely not be cheap, so I can get a saving plan in place to make that happen.

 

Ideas would be welcome for a genuine solution to this issue.  I'm hoping there are some people here with the technical know how and experience to not only suggest a solution but also eliminate any ideas that can't work.  I'm also happy to take any photographs of the current set up for reference if required.

[Station]

I've said this before, and was going to say it again in jest, but surely it would be easier to adapt MGF spheres? Tthey're only mounted in a bolt on casing to the subframe.

[vulgalour]

The MGF uses struts in conjunction with the displacers, as I understand it, rather like the Citroen system.  That means understanding where to mount the struts, which I don't.  I also don't know what the MGF spring rating is so I don't know if they're robust enough for the Princess' extra weight.

[forddeliveryboy]

I'd have the spheres regassed. It makes more sense (and would be cheaper) than re-engineering the very compact Moulton suspension to take coils, I'd have thought. There are a good number of people who've gone it alone in having the units recharged rather than using the ebay chap, I'd think there would be a decent saving to be had. But there's your time investigating what parts are needed and finding a decent TiG welder to pop the connections on, keeping the heat transfer low so the diaphragm isn't damaged.

 

If getting a spare set of suspension units means buying an entire car to scrap, so be it. But I'd thoroughly look at using MGF ones too - they're the best spec which was only used when the F came out, with lower internal friction for an even better ride. It would just be a question of playing around with pressures to create the right spring rate.

[vulgalour]

It might be worth mentioning I don't mind dropping the ride height or even losing some comfort if it means something like the more readily available MGF displacers - as little as £15 each for known good ones! - could be used.  I like the compact and clean nature of Hydragas, it's a superb bit of design, just has very poor support for the non-sporting models that use it.

 

Does anyone know if the MGF spheres can be used without the shock absorbers?  I've been told several times that you can't use the MGF spheres though I've seen no practical proof of this and the main reason given is that they don't fit as they're a physically shorter unit.

[forddeliveryboy]

Yes, the F's units are basically the same as Metros'/100s'. The damping acts in one direction, I think - for a sports car it was necessary to have damping both on bounce and rebound strokes, so a set of single-acting hydraulic dampers was added. I don't know how the damping would behave/suit a Princess, though. Ask those who've been using this suspension since the 70s, surely there's someone who'd love to pass on his knowledge?

 

Obv there would be some re-engineering to make the F's fit, has anyone actually tried yet or are most Princess/Allegro people club members, who have their own private supply of the right spheres?

[vulgalour]

Did some internetting, I couldn't find spring ratings but I could find curb weights.

 

MGF appears to be around 1070kg

Princess is around 1160kg

 

I'm guessing that a 90kg difference would be tolerable, it's about the same as a regular person so an empty Princess weighs as much as a half-full MGF.  A full Princess is going to be considerably more, but probably not excessively so.  I'll have to get some measurements for displacers, I've got a front and a (dead) rear from a Princess on the shelf I can measure and if they're near to the MGF in diameter I suspect the length can be compensated for with a little clever thinking and metal spacers.

 

I do know when you're pushing on in a Princess it can be a little bit of a handful if you try and do anything particularly sporty in the handling department so it may well be okay without the dampers the MGF makes use of and improved with.  This is the first time I've actually sat and looked at some MGF facts and figures, I should have done this sooner.

 

Displacers are hoarded, I suspect even at the expense of those that need them.  It looks like a set of MGF displacers is currently going to set me back around £200 from a quick online browse of forums and eBay if I go for second hand ones, considerably more if I go for a new modernised set.

[Noel Tidybeard]

there is an update on aro from this year regarding the re-gassed maxi spheres

http://www.aronline.co.uk/blogs/cars/mg-cars/mgftf/tech-recharging-maxi-spheres/

[vulgalour]

I had picked up on that update earlier this year and it's good that people have had some success with the modification.  I would have liked to know more about the test conditions and whether daily use puts displacers at greater risk of failure than irregular use, most of these cars only really do the show circuit and aren't used that much.

 

Conversely, I know of one owner who has never had a problem with the original displacers on his car which at least until very recently he was using regularly for everything.

 

There is one local company I know of that might be willing to do the schrader valve install, I haven't approached them because I'm not sure they'd take my request at all seriously.

[Guest Lord Sward]

The MGF dampers only worked in one direction as pointed out.  They were there just to 'tune' the handling as it was supposed to be a sports car.  Otherwise they are just better quality (front) Metro items.

[purplebargeken]

I suppose the main problem is that there is possibly not a gigantic market for such re-development due to relatively small amounts of cars requiring such things. Shame but simple market force/economics rule. Annoyingly.

 

I also reckon the MGF route is worth looking into.

[Craig the Princess]

Bumped into the eBay chap at a car show, he thinks (but he would wouldn't he) that by re-gassing the new gas at the original pressure takes a lot of the stress off of the diaphragm prolonging the units life.

 

When the price drops closer to £50 a unit I'll think about it.

 

Generally however using the Hydragas Allegros and Ambassador hasn't thrown up too many issues. One popped Hydragas unit in 10 years over 12 cars.

 

I know there was a chap in eastern Europe (Estonia I think but could be wrong) who converted an allegro to springs about 7/8 years ago. I'll try and find his report for the allegro club magazine. It was quite different to the one in the post above.

[The Reverend Bluejeans]

Up until the1985 facelift, Metros used front dampers. After that they were deleted.

[MarvinsMom]

the front dampers remained through out the run on the MG Turbo's, and the MG 1300.

 

the front dampers were deleted on the boggo spec cars.

[Asimo]

For steel spring suspension the Citroen C15D rear suspension units might be worth a look. Although they are concentric coil spring damper units they are designed to work with the same sort of suspension leverage as the Princess and are really quite compact. As they are for the rear of a van they may be up to the weight of the Princess. Any move to steel springs is sure to produce a very different drive to Hydragas but certainly a much better drive than broken Hydragas!

 

As far as the mods. to allow recharging of the gas spring go, there are lots of industrial pneumatic fittings that would be easier to use than those Schrader style valves that have been welded in by others. I reckon that there will be some connector from SMC or John Guest that is small enough to fit in the sphere by drilling / tapping and sealing rather than a critical and risky welding job.

[ShiteRider]

Would airbag units from a rangey/ merc fit?

Or go full on hillbilly banger racer and graft in a cortina or viva front clip.

[UltraWomble]

Bite the bullet and sell a kidney

http://www.ebay.co.uk/itm/AUSTIN-PRINCESS-AMBASSADOR-FRONT-HYDRAGAS-DISPLACERS-/301287984518?pt=LH_DefaultDomain_3&hash=item462629cd86

[dugong]

Rayvern Hydraulics might be worth contacting.

[vulgalour]

@SornMe: Citroen rear suspension is supposedly about the same dimensions, had a few suggested from various Citroens including the C15.  Parts are cheap and plentiful too which would make this route sensible.  The back end is the easy bit, in theory.  I'll have a word with the local engineering company too, I didn't know there was a way of putting a gas tight fitting in without welding.

 

@dugong: Rayvern Hydraulics are one of the companies to ignore attempts at contact and one of the first I contacted because of their expertise.  Disappointed really.

 

@Craig:  one a year for me on the same car.

 

 

Now I know a bit more about the MGF system and why it has the shocks it may be more tenable than previously thought, especially as there's a good amount of aftermarket support there.

[Mr_Bo11ox]

Hydragas is half the point of having one of these cars!!!! forget the steel spring idea.

[Squire_Dawson]

Do you currently have a Hydragas failure?

[MarvinsMom]

I'm going to have to get the units on the metro done at somepoint.

 

only 2 things bother me about having the re-gas done.

 

1- can actually get the units off of the car

2- will they re-pressurise afterwards.

 

changing the knuckle joints in the front axel a few years ago I found out I had a kippered valve in one unit when trying to put some fresh hydro fluid in it.

 

that time I was fortunate to be able to buy a new unit off of x-part.

 

I cannot do that now (none left!!)

[vulgalour]

@Mr Boll: agreed!  But it's no good to me if the hydragas is kippered.

 

@Squire:  yes I do and only one spare displacer on my shelf, which I hope is the correct one.  If the rear has gone instead of the front I suspect has failed then I'm jiggered.

[jonny69]

What's so difficult about the Schrader valve install that makes it cost £90? I've never seen a hydragas unit before and I don't know what pressure they hold, but when I've fitted tyre valves to things in the past you just drill a 13mm hole, de-burr it and force it in with a bit of Vaseline. The normal rubber ones can take about 160psi before they start bulging out alarmingly.

[vulgalour]

Couldn't tell you why it's so pricey, I have no idea.  The other issue I'll have is finding somewhere that can put Nitrogen back in to the relevant pressure.  I don't even know where you get Nitrogen from for this sort of thing.

[plasticvandan]

so what stops the 40 year old rubber diaphrams from perishing?

[Mr_Bo11ox]

The one between the gas and the liquid is not exposed to light or to air so it doesn't seem to perish. The one at the bottom of the cylinder does split sometimes.

[jonny69]

Nitrogen shouldn't be too difficult because it's fashionable to fill tyres with nitrogen, so most tyre places should have it. Kwik Fit definitely do. It comes in cylinders at 2750psi so pressure isn't a problem either. You just need someone who will be able to fill it up to a specified pressure rather than just whacking in about 30psi without even watching the gauge, which is what I expect most places do.

 

It's probably nitrogen in there because then the rubber doesn't perish, as Bo22ox mentioned.

[forddeliveryboy]

I seem to remember the Moulton pressures are 17-18 bar, and that tyre places usually don't have regs which will fill to that pressure. I think the idea of welding was that it's truly permanent, through vibration, freezing cold, baking hot and everything else inbetween. You don't want to have to be removing these things every so often to sort out a leaky joint.

 

Comments about £90-100 per unit sounding expensive ring true - it would encourage me to find out about having it done elsewhere, having found what parts were needed and the pressure required. And adding the ability to charge/discharge when on the vehicle, to fine tune the spring rate.

 

I agree with the guy's comment that having the pressure correct will unload the diaphragm and potentially should give it a longer life. But perhaps he's pricing things on the basis that it's a far better, longer-lasting and original option that steel springs. (The MGF forums seem full of people who have a big dislike of the 'popular' steel spring/damper conversion offered by Rimmer and others and it's twice the price.)

 

I'd avoid retro-fitting anything from another make of vehicle, unless there's someone else who has done so and found it as easy or easier than removing the hydragas units and replacing them once refilled. But it's highly unlikely. Google David Lambeth MGF and see what little bother he had in recharging the hydragas for desert rallies.

[Honey Badger]

I don't really think its a excessive cost to get the valves put in, certainly it's a price I would pay to sort out the original suspension, especially if the spheres are so rare.

 

Messing about fitting suspension that not meant for the car might seem like the cheap option but the amount of time that you could spend making it work may well kill your enthusiasm for the car again?

 

Shame you can't pump them full of a neoprene rubber/polyurethane type material that has a honeycomb like structure to replace the nitrogen and remove the worry of burst diaphragms.