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MG MGF Technical - leaky sphere?

Looks like I have a leaky sphere. I checked the ride heights 4 days ago and the near side was 6mm lower than the off side since then it has sunk another 6mm and is now 12mm lower. The brakes are increasingly pulling left and I need to get this sorted. Does anyone know where there is a description of how the suspension works and what checks I can carry out to decide where the fault lies. I suspect gas is leaking as I had the pressures checked and the offside pumped up a fortnight ago and the brakes went OK (I didn't check the heights) but now it has started again and gets worse all the time. Can the sphere be changed at home, I am competent mechanically but I have never worked on gas suspension before. Is there anything on the web about changing the sphere and does anyone know the costs involved for parts and for fitting if neccessary.
Sorry to go on but it's a worry.
John
John

John, The hydra part of the hydra gas needs a special pump, there may be a few back street garages who have one as they were used on the Metro- they should also be able to trouble shoot for you. I fear that the cost of the pump will make it ill advised to do this at home :-(
Will Munns

John,

Check Dieters web site at http://www.mgf-net.de/ for everything you ever wanted to know about the hydragas system. Click on the links with the words hydragas in them in the left panel.

As Will says you will need a hydragas pump for most suspension work. If you manage to borrow one then everything can be easily done by yourself.

Spyros
Spyros Papageorghiou

Someone here has one....
As do the Halfway House Meet people.

Will
Will Munns

A trip to your dealership for 'pumping up' the alcohol spheres was £47.00 last time i enquired. A Hydragas pump to do the job from B+G was in the region of £250.00.

5 of us at Essex Roadsters put £50.00 in the pot and bought a Hydragas pump a couple of months ago. Therefore each of us only has to use it once to get our money back, 2 of us (me included) have used it so far and as the winter draws in the others will too to keep thier trim level constant - with a lowered F, ground clearance becomes an issue during the colder months.

AFAIK the Nitrogen spheres are sealed and therefore no DIY adjustments are possible. If the Nitrogen spheres are the cause of your problems then i would imagine the only remedy is replacement.

SF
SF

>i would imagine the only remedy is replacement.

But when replaced (possible DIY?) they will need pumping up
Will Munns

Does anyone up north Cheshire/Merseyside area have a pump I can borrow/hire.
Does this pump do the nitrogen or the fluid and where do I get either of these?
john

True.

Thinking about it now, i doubt the manufacturers (Dunlop?) would charge the Nitrogen spheres in the plant and send them out under pressure (health and safety) - especially if the Alcohol sphere is empty. Therefore it is reasonable to assume that they are charged with Nitrogen in the MG plant and in the case of a dealer fit replacement, at the dealership. So presumably this means that the Nitrogen spheres ARE pressure adjustable, probably need a specialist bit of kit though.

SF
SF

Hydragas pump from B+G only does the alcohol sphere.

Sf
SF

As I understood it the gas can also be charged by the dealer - or at least one with the correct equipment.

However if the sphere has lost gas pressure then it will almost certainly mean it has a leak and they can not be repaired (again as I understand it) as the gas area is simply the top part of the sphere which is divided by a membrane - fluid in the bottom and gas in the top and the tops are not linked to each other, unlike the bottoms.

If that makes sense to you - wow!

Ted
Ted Newman

The nitrogen part of the hydragas unit is supplied sealed from the factory. You can only mess about with the fluid part. As Ted says above if you have a nitrogen leak then the unit is beyond repair. The nitrogen sphere is the one that actually provides the "spring" part of the suspension. The fluid is used for the damping action and to provide the front rear interconnection. The fluid is available from dealers, the unipart one is part number GZS1486.

Several people here have also made the own home-made pumps - look at Dieters site for instructions. This maybe another solution for you John.

Spyros
Spyros Papageorghiou

>If the Nitrogen spheres are the cause of your problems then i would imagine the only remedy is replacement.

I think so. This can only leak once... until it's empty.
Depressurise happens in about 5 minutes if you drill a 0.1mm hole to the upper sphere. Experienced when I dismasntled a broken unit two years ago. Drilled carefully with a 1mm drill until I heard the gas disappear with slight 'fart-noise'. So I prsume it was an only 0.1mm hole.

Spyros said already that 'only' the spring behavior will fail due to an empty nitrogen sphere. The dealer equipment will allow to test a single unit on whether it's gas sphere is OK or not. The unit gets pumped up with fluid for this test until the lower sphere is filled. Any more pumping will then result in big pressure difference instead of slow increase.

Anyway, air bubbles in the fluid system could be resonable for the above mentioned strange height change behavior.
The dealers pump needs exactly following the instructins to pump up the system. If they 'just pump up' then they get air into the system.
Right action is to release fluid at first after connecting the valve to the connection and then pump up.

You can easy check whether air is inside.
Open the bonnet and remove the spare wheel and wiper motor cover.
See that the ambient noise is calm for better concentration on low noises. Now bounce the car at the front right or left and try to hear the fluid flow.
If air is inside then you will hear a clear flow noise due to expanding airbubbles.

Hope this makes sense and you get what I mean.

HTH
Dieter
Links on this matter:
http://www.mgfcar.de/hydragas/ehydragas.htm
http://www.mgfcar.de/cut_unit/index.htm
http://www.mgfcar.de//pump/index.htm
http://www.mgfcar.de/defects/blownhydra.html
http://www.mgfcar.de/defects/blownhydra2.html
Dieter Koennecke

Thanks Dieter I'll try that. If there is air in the system I don't think that would cause the ride height to sink as the air would be at the same pressure and therefore volume all the time unless it is being absorbed into the fluid?
John

John

Air compresses - a lot

Fluid does not.

Ted
Ted Newman

I have just noticed that our car has dropped on the nearside. Is is worth having this pumped up, or will there always be a fault with one of the spheres?
I guess these spheres are similar to central heating units - they have fluid on one side of a rubber membrane, and gas the other. Presumably, the fluid filled side is the "push" (spring) side, so if the fluid leaks the car goes down.
T Green

Ted
Air does compress more than fluid but if the pressure remains the same the volume won't change and so the height of the car should remain the same unles it gains some extra weight from somewhere or there is a significant reduction in temperature.
Can't we go back to springs this hydragas gives me a headache!
John

John

Nice theory - but - there should not be any air there to start with. So if air is getting in surely fluid is getting out!

Air in an hydraulic system is bad news.

Ted
Ted Newman

Too true Ted, perhaps that's why it did some gymnastics at a roundabout recently, must get it sorted over the weekend or put it in the garage.
John

If you want to see how far you can go with this suspension see the info on www.dpr-racing.co.uk/tech_hydrolastic.htm
Derrick Rowe

Thanks Derrick I'll take a look at that. IT seems a complicated system just to take the pitch out of the body but as I'm stuck with it I'd better get to know it.
Johnh

This thread was discussed between 09/08/2002 and 15/08/2002

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