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MG MGF Technical - MGF Sagging. Pls Help


Hoping someone can help me out.

Over the past few weeks I have noticed my car scraping against the ground when i drive over the speed hump at work which I have been driving over for the past several years. This is esp noticeable on the right side (it is a mk2 mgf late 2000 model)

Thinking (and hoping) my tyres were abit flat I topped them up with some air--but with no improvement.

I had a closer look today and it looks like the right rear of the car is sagging. The clearance between the tyre and the body of the car is noticeably less.

I have had the hydrgas pumped up last year or so. Would this be related or is it something else? Shock absorbers?

Should I take to an MG repairer or would the local garage know what to do and look for?

Your help is much appreciated.


Daniel M

Right rear? Unfortunately, this could represent a failed hydragas sphere Daniel. Inspect the car, and check all the ride heights at each wheel. If disproportionately down at one corner, then the likely answer is a failed sphere.

I gather that new replacements are getting increasingly difficult to source (see Hydragas survey over on the general board) - but they're still readily available for reasonable money on ebay in the UK.

Interesting that you're in Australia - there seems to be a disproportionate number of hydragas failures from your neck of the woods. You may also be interested that there is a company looking to manufacture a coil-spring conversion...
Rob Bell


Thanks. Will have a look.

Not having much luck with her recently...6 months ago the alternator went.....whats next ? :-(


Daniel M


I have measured the distances between the centre if each wheel to the wheel arch directly above and have got

Front Right and Left 31.0-31.5 cm approx
Back left 32cm
Back right 30.5

(my understanding is that it is supposed to be about 37cm)

Would this be consistent with a broken sphere or it it possible to get asymmetrical sagging if the hydragas needed topping up?


Daniel M

I have just had my F serviced here in South Australia. The hydragas was topped up as it was scraping speed humps but I have also been advised that one of the hydragas units has a gradual leak. I am getting this fixed next week. It sounds like you may have a similar problem?

I am seeing AA Motors in Magill SA and Adrian has the (new) replacement units at his workshop.

I'd get to an mg specialist if I were you. Current monsoonal conditions permitting :)!

How is your tyre wear going? I now find that I have uneven wear on my Toyos that have done not that many k's since mid 2009.

hope this helps
A Steventon

Daniel, I'd get the system re-pressurised. As you say, standard suspension should be around 36-37cm from wheel centre to the wheel arch vertically above (dependent upon ambient temperature), so yours is extremely low on both sides.

I wouldn't condemn the 'spheres just yet. See how things look once the system has some fresh hydragas fluid pumped in :o)

Fingers crossed!
Rob Bell

Daniel, sadly I fear you'll find that the rear Hydrogas units are now almost impossible to obtain.

However, here at the Classic Car Clinic in Biggera Waters, we are looking at importing the spring / shocker conversion Clive Berry has discussed elswhere on this forum.

I already have at least one other client waiting for 'news' of their arrival, I will place an order with him as soon as I have enough interest.

Call me if you would like to chat about it....

(07) 5529 1876
M T Boldry

Depending on how a rear hydragas sphere fails, it may in fact be possible to recover it.

If a membrane has failed, then I fear that it is scrap. You may see fluid pouring out of it (as Dieter did on his car - twice! - - or you may not, if the nitrogen/fluid separator fails.

If these are intact, then it should be possible to TIG weld a screw-thread attachment in place of the rivet at the top of the nitrogen 'egg' (the top of the Hydragas sphere), and screw-in a Schrader valve (rather like a tyre valve) and then re-charge the nitrogen.

I've been in contact with Dr Moulton who is helping me find out what the OEM nitrogen pressure spec should be on the standard Hydragas sphere - and once I know this, will let you know.

However, a single corner failure is perhaps a little more suggestive of a membrane failure. :o( However, given that your car is low all round, I think that this is more suggestive of general nitrogen leakage, and a hydragas fluid recharge should be capable of recovering the car. Ultimately, you like me will need to think about the nitrogen gas recharge route - but you should get another 5 or 10 years out of the system before that becomes necessary.
Rob Bell

Hi All

My car is due for a service in a few weeks so will get the mechanic to have a look at it.

He is am MG specialist so hopefully will know what to do.

Will keep you all informed-hopefully it just needs a top up.

Thanks for your advice


Daniel M

Daniel, if it has failed, can you find out whether it has leaked hydragas fluid, or whether the nitrogen/fluid separator membrane has failed?

Hopefully neither - I suspect that it'll respond nicely to a re-charge of the fluid :o)
Rob Bell

With my own rear hydragas membrane failure in fresh memory I wonder if the following would be of any use;
A rubber block with the appropriate cut out to place between the roller foot and the sphere in case of total failure, (usually far from home !) One can then just use the jack,remove the wheel and slide in the rubber block. This will at least create a "limp home" opportunity..
If any of the aftermarket guys did such a block I would not hesitate to buy one to have in the booth. At least until the final solution with a new developed system can be bought ;O) / Carl
Carl Blom

Fluid loss Carl?
Rob Bell

More like a total loss ! Punctured membrane together with a lot of rust around the inner valve forced the Green Frog onto a trolley to get home. If I have had some slight compessable rubber to force in between the roller foot and the sphere I could have limped home. IMO one has to be VERY careful when repeated refills of fluid are needed ! After some time the faulty unit will fail completly. Lucky to find a new right rear unit and refill the system with homemade fluid with REAL rust-inhibitors.. Beware if the fluid is yellow/red instead of clear light green.Now we are all waiting for some clever solution to the problem.A straight bolt on /exchange unit for all 4 corners would be wellcome !
Carl Blom

Thanks Carl. Been chatting to Moulton developments regarding the issue of Hydragas longevity on the MGF. No idea whether there is a better hydragas-related solution, but I know of one very well-known engineer who is very keen to try and preserve this suspension system ;o)
Rob Bell

Rob, as far as I can see the two main problems with the hydragas suspension system is the spheres leak nitrogen and the fluid expands and contract with changes in temperature thereby altering the car's ride height. Would it not be possible to replace the nitrogen with some form of latex or similar? this would mean no more leaks and the sphere would therefore last a lot longer. Also, could the current mixture of antifreeze and water not be replaced with a fluid that is less susceptible to changes in temperature meaning that the ride height would change very little with outside temperatures? I can understand that MGR were looking for something cheap and cheerful for mass production and that something like what I'm suggesting would be more expensive, but in the long term it would keep the cars on the road and work out cheaper than replacing the MGF suspension with the TF type setup.
David Clelland

Agree with you David, the rubber cones worked fairly well on the old MINI ! There are very small ball-shaped springs on some cars on the market. The rear coils for SAAB 9-3 is one type. Maybee there could even be some spring action placed inside the old upper sphere ?
Carl Blom

Keep the fluid interconnection, but use a steel springing medium? Interesting...
Rob Bell

Hi All,

Just a quick update.

Took the MGF to the mechanic and (for once!) luck was on my side. Apparently all the suspension needed was a topping up!

After the hassles of the previous service (the alternator needed replacing....trouble getting an alternator....) it is nice to have a relatively straightforward servicing.

BTW, just got a BMW 120i for my wife. Lovely car. I wish BMW had put its heart into the MGF. Imagine what kind of car it would have been!

Thanks again for everyone's comments

Daniel M

This thread was discussed between 02/03/2010 and 07/04/2010

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