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MG MGF Technical - Hydragas unit availability

Further to the thread regarding replacing Hydragas units with coils, I was wondering what will happen when, in years to come, you have a unit failure, but the things are no longer available.

Won't the spring issue need to be solved.

I think the SMMT have an agreement to keep spares going for 10 years after a vehicle manufacture ends, though I could be wrong. And surely volumes mean price could be heafty.

And what about the more specialised nature of the Trophy units, for example?

Surely it must be possible to develop a spring conversion kit for the F, that delivers excellent road holding and a reasonable ride.
What would Rover have done if they hadn't had hydragas in the parts bin?

I want to hang onto my 'F for years to come; I certainly wouldn't want to scrap it just because of Trophy hydragas unit availability! Or should I stock up!

And it would be quite nice to stop it going up an inch in hot weather!

Must admit though, it's handling like a dream at the moment!

Chris, you are quite right. Where I live hydragas units are unknown and repair of my car is going to be extremely difficult. But when you think in the years to come, what is going to happen to the many Fs around the world?. Are they going to become classic cars as we all for sure wish or will just go the way of the scrap yard?
Richard Hemphill mentioned that a conversion to coils is possible. Richard, we are all waiting.
Rob Brown

I most agree with you both chaps. Hydragas system is time consuming and maintainance is very expensive in my experiance. And as my car get older suspension failures are becoming worse. I will be delighted if a suitable affordable suspension conversion comes into scene and will go for it with no hesitation.
Ian Millar

I had a HUF -hydragas unit failure- about a month ago. All of the sudden the car was slanted to the left and green fluid was emerging from the left rear unit. Fortunately I got in touch with Victoria -havenīt met but she sounds very nice at the phone- and got a replacement from MGF Centre. However the car is not fixed yet as the "technicians" are studying the workshop manual to learn the necessary know-how.
Count me among the worried people on the future of the Fs. I would also like to have an option for when my F suspension finally gives up and hydra units are unavailable -owning a vintage car I know that the time will come-.
JM Vega-P.

I thought this might provoke a bit more response!;-)

Am I completely off-beam, or is this a "sweep it under the carpet" matter?

Hardly off beam Chris - this is going to be a serious issue in the future as the Moulton Dunlop Hydragas spheres are no longer manufactured. There are, therefore, only a finite number of hydragas spheres left in the world.

Nothing to panic about just yet (well, certainly not those of us based in Europe, and particularly the UK) as there will continue to be a ready supply of either new old-stock units or used hydragas spheres from salvaged cars for the foreseeable future. Plus, hydragas (at least in northern Europe) has a very long service life. But the time will come when trying to obtain replacement parts for hydragas suspended cars is going to become prohibitively expensive :o(

Unfortunately, no steel-sprung conversion kit is going to be a patch on the original hydragas system in terms of ride/handling - so my option would be to stock up on hydragas spheres!!!
Rob Bell

I think I posted this link before. If you can convert a metro to springs then you can convert an MGF. I haven't researched the spring supplier but it looks as if a modified subframe was used.
Ken Waring

1- Ken, most interesting indeed!. I have that pic but did not know where it came from. could you signal the author in order to get some drawings of the conversion?
2- Rob, in the while and until a conversion result feasible I think I will follow your advise. A few questions however: How many spheres to have? Most rear or front?. Any special condition for stocking up -like empty or full of hydra fluid, keep cold, etc-?
JM Vega-P.

Well i have a metro its not a f but the engine is =), i have done a coilover conversion on the front of the metro and took the hydorgas units out so i agree with Ken Waring the f cant be much different.

On first hand the problem is finding the _right_ coil spring.
Had some tries calculating the spring rate years ago, when I was p***d off from Sir Moulton.
I recall estimation of app. 16k Newton for each (max total load), but how should be found a fitting spring ??
(average spring load is car weight divided by four, of course, so app 3.5k Newton)

Btw. I know love HGU's !!. Have already a pair of spare in the garage and I'm 51 !
Plus 10 years, OK, I'll get another buch of them to last the remaining couple of _my_ MGF living years ;)
Dieter K.

Very interested Andy. Could you perhaps provide a few pics of your coil conversion?
JM Vega-P.

Details of a conversion coming soon, as an ex motor vehicle technician i have in the past converted numerous mini mg 1100 and metro successfully, i am working on the mgf setup at the mo and when i know that it can be done the way i am planning , which will be a cheap conversion but will need some welding skills to do i will let you all know.
Cheers for now
R J Hemphill

Wow - I hadn't realised that so many enthusiasts were already converting hydragas converted cars! Ken, I see that your conversion is of a Mini Clubman - have you used an MGF front subframe in your K-series conversion?

Robert - I look forward to hearing more about your conversion plans!

Mike, Dieter can probably correct me if I am wrong, but the front and rear hydragas units are identical, so you just need a couple. The differences in spring/damper rates between the two units are provided by the different shapes of the alloy displacer cones that site inside the unit, above the 'knuckles' - remove this from your existing hydragas unit, and insert into the new one. Then reconnect/ recharge the system and away you go (sounds so easy doesn't it? LOL)
Rob Bell

This is not my conversion but a site I came across when I was also researching a spring conversion. Maybe we should be looking at a method of pumping the hydragas unit to create active suspension. Just a bad thought.
Ken Waring


I've never checked the ally piston length of two different. Sounds reasonable, though.
I still wondered how MGR could make two with different upper sphere pressure or different inner valve block. (this was said years ago)

Will do as soon as I can re-locate the HGU's in any of the forteen MGF part moving boxes in the dark garage ;)

Keep you posted.
Dieter K.

To the best of my knowledge the part numbers for front and rear HGUs are different which would suggest the internals are different. Certainly the alloy cones that fit into the bottom of the HGU are different front/rear which would give a different rise of "spring rate". One might think that the internal Damper rate would be different given the different unsprung masses that need to be controlled. WRT to the differeing gas pressure in the upper sphere, the MGF Cup cars had less gas giving a harder spring. It is easy enough for the manufacturer to decide on the pressure at the time of of filling them. As indicated at an earlier point I have made mine adjustable both in terms of the nitrogen gas pressure in the upper reservoir and the alloy cone for triming the ride height. To date it has been working really well. Like many before me I found the subframe somewhat flexible when I increased the rate of the anti-sway bar so have fitted it (front) to the underbody rear of the subframe pick-up points. This was suggested by someone on the BBS recently and having done it I find the car is now more sensitive to adjustments of the bar whereas before the adjustments made little difference. It is apity I don't live in the UK so that I could go along to see the MGF Cup cars and what they are doing and so stiop re-inventing the wheel!

Still, it is all good fun. Haven't got back onto my brake disc research yet..........perhaps next week if I have time.

d mottram

So at the end of the day I gather that it would be necessary to stock up front and rear hydragas units as the lenght of the pistons are not only the only difference. I will be grateful whether someone may confirm that HGU are, or are not, interchageable front and rear.
JM Vega-P.

The key word here is 'affordable'.

Anything is possible given enough money, a very significant portion of the mgtf development budget went on the suspension and although the development costs of the TF were small in industry terms (through necessity) to the layman the sums are positively huge.

Remember, we are not simply talking about a straight swap, this will result in at best a poor handling car, at worst something dangerous to drive.

It's not just a case of swapping spheres for coils, there are large subframe modifications and substantial bodywork changes needed. We know the shock mounting points aren't strong enough for any more than the minimal force applied by the standard suspension, the TF gets round this by mounting the shocks elsewhere. We also know there are space issues at the rear - this is the official reason for going with Hydragas in the first place - it is a compact system, one look at the differences between the F and TF rear suspension will confirm the amount of work that was needed to get the suspension to fit and work.

To recap, the TF suspension is mounted in a different place on the bodywork and is suspended from a different point of the subframe, particularly at the rear, with additional cantilever arms.

To some extent we have an advantage in so far as MGR have effectively done the work for us with the TF - the labour involved in modifying the subframes and bodywork to take the new coils and shocks is likely to be similar to the cost of fitting TF subframes and suspension IMO. In both cases you have to remove the subframes, strip them of componentry (which includes the engine on the rear one). The jobs then diverge, with the F subframe you have additional labour and parts involved in modifying it to take the shocks/springs - this is likely to come out to a similar amount of money as new TF subframes. The jobs then converge again, as in both cases the bodywork then needs a lot of work to modify the suspension mounting points.

So, we are not talking a few hundred pounds here - considering the 'engine out' and significant body and subframe modifications, we are talking a few thousand.

I would be surprised if the conversion cost less than 2-3000.00, labour alone is going to cost around a grand, i can see this job taking at least a week and that's 1400.00 based on a low 35 an hour rate.

But, as i started off saying, if you want it, it can be done - for a price.

Scarlet Fever

David, you could be right about the hydragas spheres - although the different part numbers could be explained as being different 'assembly' numbers (as the hydragas spheres are sure to be shipped complete with different displacer cones), I am sure that the different numbers could also mean different gas pressures and different internal valve characteristics...

Look forward to hear what you're able to discover Dieter! It would be good to get some further confirmation regarding this! :o)

>> Like many before me I found the subframe somewhat flexible when I increased the rate of the anti-sway bar so have fitted it (front) to the underbody rear of the subframe pick-up points. This was suggested by someone on the BBS recently and having done it I find the car is now more sensitive to adjustments of the bar whereas before the adjustments made little difference. <<

Glad to hear that you found the suggestion helpful David! :o)

>> It is apity I don't live in the UK so that I could go along to see the MGF Cup cars and what they are doing and so stiop re-inventing the wheel! <<

Talk nicely to Dieter, and he'll point you towards a comprehensive MGF Cup car photogallery that he put together following a Treffen visit to Spa back in 2000... ;o)

You'll be interested to know that the Cup car mounts the brake master cylinder above the brake pedal on the bulkhead, doing away with the torque bar across the car (I *think* that this was done due to crash regulations...). I'd really recommend you chat to Roy & Marvin @ Techspeed who were instrumental in the development of the cup car - as they are sure to have suggestions that'll help you avoid re-inventing the wheel!
Rob Bell

Rob, I'm sorry I didn't remember it was you re. the mounting of the anti-sway bar........thanks for the advice. This last weekend I in fact completed the mounting of a pair of master cylinders onto a fabricated pedal box mounted on the firewall directly in line with whwer the pedal actuation rod emerges into the front compartment. This did away with the torque cross bar and the booster. I have fitted a balance bar between the original actuation push rod and the new pushrods to the pair of master cylinders. Late this week I will try it all out on the road. At this stage the pedal feels too hard and I will no doubt need to increase my hydraulic ratio to compensate for the lack of a booster. My original intention had been of cpourse to fit the larger discs to alleviate part of that problem but as we know that has not worked out this stage! I suspect that I will need to reduce the master cylinder sizes to increase the hydraulic ratio without having to think about altering the mecahnical ratio of the original pedal arrangement. Certainly the pedal box has eliminated the flex inherent in the original strange arrangement. Ah, the joys of development.


PS. Dieter..............MGF Cup photos?
d mottram

David, even the MGF Cup cars retained the original servo. I've been looking into the archives for Dieter's pictures - but unfortunately, it looks as though the original directories have now been deleted :o( He's probably been trying to save bandwidth and storage space! LOL

Spotted on Stefan's site a picture of the front subframe/ front ARB arrangement on a Cup Car: Sadly, Stefan doesn't appear to have any pix of the underbonnet area.

I wonder if Eric has any images?
Rob Bell

MGF Cup car photos...
are at Erik's site and several Treffener pages and the one and only Silverstone visit I had in 99.
(bad Quality, apology)
(with link to Erik's old domain)


Dieter K.

Erik has got some images on his site - trouble is the links don't work - turns out that a '/' has been substituted for the '/' in the URL...

The second of Dieter's links (thanks Dieter) was what I was looking for. Dieter I thought you might have had a more general shot of the front bonnet region?

Two images of the region of most interest are:

The latter showing the support bracket for the servo/master cylinder where it has been repositioned in front of the driver.
Rob Bell

I wonder if any of you people could provide address either postal or electronic of Dunlop-Moulton Ltd.
I would like to find out from them how long will they keep on producing hydragas units for the MGF.
Derek Foster

The address ? Would like to know as well.
See for any Dunlop manufacturinng site.
I think they hold the patents. (IMO)

Had simple researches over the last years about Sir Alexander Eric Moulton.

btw, this patent may be of very interest. :)
(US patent server, EC based charge for research)
(follow up to patent No. 108761 from 1971)
However, there are later with linked hydragas units. I think from 1976.

Dieter K.

Derek, Sir Alex Moulton now has an engineering consultancy and a bicycle manufacturing operation in the West Country - but doesn't have anything to do with hydragas sphere manufacture for automobiles any more.

Not sure what manufacturing site was used for hydragas - probably somewhere near Birmingham. It'll be a Dunlop facility if that helps you in your search.

To my knowledge, all manufacturing for hydragas stopped with the introduction of the TF in 2002. :o(
Rob Bell

I would rather sell the F than making a conversion.
I want to keep it with the original technical features. A F without hydragaz is not a F. It would pointless to keep it.

Question is Arnaud, who are you going to sell the F to if common knowledge spread that hidragas units will not be available in a few years for now. I will love to keep my F to become a classic car and to be able to drive her in the distant future. Now, will that be possible if we F owners depend on a single part that is not going to be available nor reproducible by the way of a conversion?
JM Vega-P.


Well, the buyer will make the conversion if he wants to. But i won't.
There are better cars on the market but few have as much originality as the F. Losing the Hydragaz makes the car losing a lot of her atractiveness IMO, up to a point i would prefer to sell it.


This thread was discussed between 08/12/2003 and 21/12/2003

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