The Hydragas Problem - seeking a solution

[Bear]

If you read Alexander's article on ARO, you'll see the Hydragas cans should be charged to 1/2 to 3/4 of the fluid pressure.

 

On an MGF, the fluid pressure is 400psi. On older Hydragas cars it looks like it would be 250-325 from a quick google.

 

So, the rubber valves capable of taking 160psi MIGHT work, on a softer ride setup.

[Pillock]

But if they're filled to 160psi stationary, won't that rise as you hit a bump or go around a corner and the weight shifts? POP.

[dave21478]

yep. I would be wanting at least a 50% safety margin to cope with a sudden pothole.

 

 

Someone mentioned above about re-welding (or rivnut as may be) the existing displacers.... "not a lot to lose."

Thats the important bit IMO.

 

Screwing it up and ending up with a scrap displacer is a bummer, but a second hand replacement will come along sooner or later. Better that than cutting half the car away to graft in suspension from something else and finding out half way through that its not going to work or the skills required to finish it properly are too high.....thats the end of the car.

[Bear]

Well, the Citroën spheres installed remotely would have that margin. Perhaps a slower response? Trying to think in terms of fluid moving - larger volume, longer to equalise between ends of the car, slower reaction I think?

 

My gut feeling on this is that from ADO 16 to MGF, all Hydrolastic/Hydragas spheres should be assessed to work out a displacer that could fit in all applications, and then a contact made for Chinese manufacturing of a split canister type - a bit like the earliest Citroën spheres - with a viton membrane and recessed valve with screw-in cap for refilling. This module could then have a choice of screw-in valves to provide the different rates for each application, and then simple engineering plastic or metal carrier adaptors mounted to allow them to fit the intended car. For Hydrolastic cars, the sphere would be a rubber spring.

 

This would also have the interesting option of equipping earlier cars with Hydragas, or later cars with Hydrolastic, depending on the performance wanted, and it would also allow improvements on cars like the Allegro, where higher-pressure Hydragas with appropriate damping could presumably get the ride & handling up to - or better than - R6 levels.

[Lacquer Peel]

Transverse leaf springs off a Ford Model T.

[mouseflakes]

My gut feeling on this is that from ADO 16 to MGF, all Hydrolastic/Hydragas spheres should be assessed to work out a displacer that could fit in all applications, and then a contact made for Chinese manufacturing of a split canister type - a bit like the earliest Citroën spheres - with a viton membrane and recessed valve with screw-in cap for refilling. This module could then have a choice of screw-in valves to provide the different rates for each application, and then simple engineering plastic or metal carrier adaptors mounted to allow them to fit the intended car. For Hydrolastic cars, the sphere would be a rubber spring.

Yes, that's one approach. Alternatively, could you just stuff each of the old units with a Stretch Armstrong?

[twosmoke300]

I was going to suggest if you could fill them with liquid rubber similar to they use in ag equipment tyres . Then fit a damper somewhere

[mouseflakes]

liquid rubber similar to they use in ag equipment tyres

 

They fill those tyres with dead Stretch Armstrongs. They go a bit runny post mortem.

[rovamota]

Don't forget, the Princess suspension was designed to carry not only the weight of the car, but 5 adults, their luggage and maybe even a caravan. I don't think MGF displacers would cope.

[Lacquer Peel]

Has anyone tried? From a layman's POV, I guess the MGF is set up to deal with higher cornering forces so might cope with the GVW of a Princess.

[M'coli]

MGFs are a Metro front set-up at both ends, so it's not really going to be up to carrying the mass of a fully-laden automatic 6-pot Princess, I feel.

[vulgalour]

Rovamota, didn't you cut a dead displacer open to show the construction?  Or am I thinking of someone else.  That could be handy here.

[cobblers]

Rovamota, didn't you cut a dead displacer open to show the construction?  Or am I thinking of someone else.  That could be handy here.

 

[Taff]

MGFs are a Metro front set-up at both ends, so it's not really going to be up to carrying the mass of a fully-laden automatic 6-pot Princess, I feel.

So use two of them, double up.

 

The lack of Princess suspension units is only of concern to 7 people on the entire planet.

 

It's Gods way of saying "weigh them in, they are shit....". I learnt to drive in one of the fuckers and I have despised them ever since.

[Bear]

Don't forget, the Princess suspension was designed to carry not only the weight of the car, but 5 adults, their luggage and maybe even a caravan. I don't think MGF displacers would cope.

 

I think that might be why the MGF is running 400psi fluid and doesn't pitch and wallow. My memory of the Ambassador my dad had (for a mercifully short time) was being wobbled and pitched to the point where anything over 3 miles included one guaranteed puke-stop.

 

And the MGF weighs 1100Kg or so. Princess isn't that different with the 1.7 - but, this is the thing with oleopneumatic setups, the size of the egg isn't actually that important. GS spheres or XM spheres, they're all pretty much the same - the valving changes, but a 1650kg XM has the same spheres in terms of volume as a sub-1000Kg BX.

 

And corner loads on an MGF - I routinely fling the MG into corners at speeds an 18-22 couldn't attain in a straight line with a run-up, and yet it's one of the most accomplished cars this side of a Hydractive 2 Xantia/XM at shrugging off mid-bend irregularities.

[vulgalour]

I feel I must defend the Princess a little bit on the handling front.  It's no sports car, it's true, but it's not wallowy when the suspension is in good health as mine has been briefly in my ownership.  It'll go into corners quicker than you think it should and if you ignore the factory 24/26psi in the tyres and bring it up to 28/30psi then it's even better.

 

You're right though, the lack of units is only a worry for less than a dozen people mad enough to want to pilot the old wrecks about the place.

[plasticvandan]

you dont need suspension when its parked in a unit?

[LC Torana]

you dont need suspension when its parked in a unit?

 

Oh that's just below the belt.  Some of us just take a while to get our project cars on the road.  Life happens, there's no shame in that.

[Bear]

I feel I must defend the Princess a little bit on the handling front.  It's no sports car, it's true, but it's not wallowy when the suspension is in good health as mine has been briefly in my ownership.  It'll go into corners quicker than you think it should and if you ignore the factory 24/26psi in the tyres and bring it up to 28/30psi then it's even better.

 

You're right though, the lack of units is only a worry for less than a dozen people mad enough to want to pilot the old wrecks about the place.

 

It's not a matter of needed to defend it - totally different expectations, the Landcrab and Princess were both pretty well regarded outright and downright impressive for the time.

 

And that dozen people becomes many, many more when you add all of the cars together then seek a unifying solution...

[rovamota]

Princess displacers side by side (rear displacer on left of picture).

 

Front (left of picture) and rear damper pistons removed.

 

[plasticvandan]

Coil overs?

[Squire_Dawson]

If the blueprints survive they could be made again, but not on a commercial scale because there is almost zero demand. It would have to be a specialist job, or fabricate them yourself provided you have access to the right facilities.

[rovamota]

Dunlop were approached to remake them. They wanted £50,000 up front just to tool them.

[Bear]

The biggest issue I can see wouldn't be tooling or manufacture - this is why we have the tech we do these days - who needs tooling and huge up-front investment when a five-axis milling machine can work with a block of alloy billet and produce something stronger, at maybe 10% more material cost that would make a big mass production firm baulk but many owners would absorb.

 

It's the type approval. How would a replacement displacer be approved for fitment?

 

Are the Princess displacers valved differently for front & rear?

[Asimo]

It isn't the metal bits that are the problem really, it is the very carefully designed and made rubber bits. To start from zero and succeed with a steel part is one thing but to do it with (say) Hydragas diaphragms in reinforced Butyl is something else entirely. Even if one had the drawings, you'd still need the process resources of a Dunlop to succeed in actually making them.

 

I don't think type approval is an issue is it? No type approval required for lowering springs or fancy dampers. In the UK at the moment.

[Bear]

I'm thinking to make remaking them worthwhile, you need a global market.

 

I think the rubber is not that hard an issue to solve, as we have computer modelling now, and better materials. Some of those better materials are pretty recent, or just cost more than mass production allowed - like, for example, upgrading all the Merc's hydraulic roof rams to Viton seals - the material existed, but it cost more.

 

And I don't think you'd need the resources of Dunlop, but I do think there'd be an element of Heath-Robinson about it - but the kind of Heath Robinson that the MGF or Metro Cabriolet is, rather than a Scimitar SS1 pre-galvanised. Look at the short run products people make with Kickstarter backing. And hey, £50,000 - peanuts for some Kickstarters.

 

What would really interest me is if some proper understanding of Hydragas physics could then allow something new - retrofitting Hydragas to other cars. I always felt the A-class would have been a much better package on Hydragas - that has the issue of McPherson strut front suspension.

[vulgalour]

I can't find it, I've been hunting for it to no avail for the past few days, but there was a supplier of super compact coilovers designed for installations with limited space that would have been ideal as a replacement in the displacer locations.  It was reported that the ride was pretty firm and you had to want a low ride height but the idea was neat.

[Noel Tidybeard]

what some of us need is a pic of princess/allegro/maxi spheres next to an mgf set so we understand where the problem is

[vulgalour]

Princess displacers look like this.  Front and rear have different metal cones in them and aren't interchangeable.  Rears are in special brackets that are handed and again they aren't really able to be taken in and out of the bracket without destroying said bracket.  Second picture show a rear displacer with the bracket cut away, bit of a nuisance to put that back together strongly really.

 

 

MGF type displacer.  Much shorter and I'm pretty sure different in every dimension it can be. I've not had hold of an MGF displacer to measure the external size of it but I suspect it will be too narrow and short to seat properly on the Princess and require re-engineering of the rear displacer brackets.

[vulgalour]

 

Hmmmm