NSF ride height low post pothole

[Mike63]

Hi All. My wife hit a pothole that then threw her into a kerb which blew the tyre. Now the NSF ride height is 13.5" to the metal whilst OSF is 15". I Don't see any damage to the swing arms so I infer the suspension unit is damaged. What puzzles me is why the ride height on both rears is the same: if the unit has 'ballooned' due to the shock then I'd expect the lower pressure to drop the NSR as well.
BTW I bought a hydraulic pump and set the heights maybe 4 years ago: an adapted grease gun, might have been ebay. It is now rusted internally completely solid.
Mike

[Charless]

It sounds like the membrane has gone. Luckily the NSF is the second least awkward sphere to replace! Have you tried regassed spheres all round? Now could be the moment - the difference is astounding.
You can buy an oil gun on ebay and transfer the hose with adapter. Although you might be better off buying a central heating test pump and adapting that to take the hose-with-adapter.

[RobboMC]

Since it's 20+ years old the other spheres won't take much more use.

Time to do the full set or change to coils.

The hydraulic pumps do need to have the water flushed out of them after use, since we only use them annually or less.
I always used some 100% coolant as a final rinse.

[Mike63]

It sounds like the membrane has gone. Luckily the NSF is the second least awkward sphere to replace! Have you tried regassed spheres all round? Now could be the moment - the difference is astounding.

Now you mention Charless, Rover did call it 'hydrogas'. I've owned minis on rubber and this MGF on hydrogas, and I just picured it as a the mini rubber donut with a central fluid chamber. From your description, I now picture a gas shock absorber with compressed N2, and the antifreeze is the other side of the membrane, connecting front n rear. The MGF does have unusual behaviour over bumps compared to, er, normal cars. It jumps left and right based upon which front wheel hit the bump: hence the assumption that it's connected front to rear same side, which is the perfect anti-roll set-up. So, what you're saying is, my car now has 'the bends' because the anitifreeze has N2 bubbles. Equally, the sealed chamber that was just N2 was a significant portion of the ride height spring. So, for just the NSF to have dropped, the N2 is at significnatly higher pressure than the anitifreeze, in its own sealed chamber. Front to liquid rear is now at a lower net pressure, but rear still has the high pressure N2 spring.
Did I get that right? If so, is the NSR now under risk of bursting the N2 chamber?

[Mike63]

Since it's 20+ years old the other spheres won't take much more use.

Time to do the full set or change to coils.

The hydraulic pumps do need to have the water flushed out of them after use, since we only use them annually or less.
I always used some 100% coolant as a final rinse.

Well, I've taken Essex CC to court as the org that contracted Highways England, whose defence appears to be 'we walked along the road every 3 months as required'. My argument is that just inspection isn't sufficient to invoke their Statutory defence. Subsidence on the off-side caused her to counter-steer away from the schoolkids on the pavement, so when the NSF dropped into the 6cm pothole, it blew immediately. Sidewall of the NSR was damaged, so both were replaced. Now it sounds like the suspension unit was stuffed too. ECC solicitor had the cheek to accuse her of, in marginally different words, 'careless driving', for avoiding kids rather than potholes! They confuse themselves with the Police. And it sounds like the bill is going to rise.

I'll dig the instructions out for the pump I bought: I don't recall your helpful advice RobboMC. I flushed and then blew it through with compressed air, but it sounds like leaving 100% antifreeze would have been better. Or in a box with silica gel. V. annoying becase it wasn't cheap. The body is clearly standard grease-gun, but I'm surprised that any oil can could reach such pressures.

[Charless]

Whilst standard grease guns will work at first, their seals are not needed to be of the highest quality to work with viscous grease. Oil gun seals tend to be better as they have to reach higher pressures to get through valves which is useful working with the viscosity of basically water for our suspension. Obviously generic grease guns are much easier to come by and are frequently advertised as grease/oil guns.
Good luck with the case - there will be an avalanche of metoos if you win!

[Mike63]

Good luck with the case - there will be an avalanche of metoos if you win!

Thanks Charless! Two tyres and now at least one suspension unit, so I'm in fightin' mode. I've been bumped from Magistrates to Crown Court already so I think they've got the message

[Mike63]

Help! After pothole, we drove the car nearly 1k miles to the highlands and back. It was clear that the car was riding low at the front as I scraped over speed humps in Glasgow. On return to Essex, NSF was 1.5" lower than OSF whilst the rears were at the same height. I took the car to an MG garage, ~25 miles, and there we measured NS low front and rear. Garage didn't think suspension diaphragm had blown so recommended just re-pressurise to reset ride hight. I'm confused. I think if the membrane between the N2 and fluid failed then both NSF and NSR would droop because the gas and fluid are now connected: or increase, because the N2 chamber sets ride height so pressure is >> fluid pressure? Is there a definitive test to determine if a suspension unit has blown? Thanks! <M>

[Rob Bell]

Hi Mike,

As standard, the MGF suspension units are interconnected front to rear. If there is insufficient fluid, the whole side will drop.

A single wheel being at a different ride height to the other three units does, to me at least, suggest an internal failure of the NSF hydragas unit - as Charles suggest, likely a ruptured nitrogen/fluid membrane.

There is some spiel on hydragas and its workings here: http://mgf.ultimatemg.com/group2/suspen ... _index.htm

[Mike63]

Hi Rob,
Charless' explanation made sense based upon my understanding. I'd pictured the N2 as the bottom donut but I see it's the top. Why NSF was 1.5" down and the other 3 were fine *after* 1k miles round the highlands? Maybe some peculiarity of the fluid damper valve in the NSF unit. After I went 25 miles to the MG/Classics garage, he took it out for a test, said it had good ride compared to others. On return, NS was low both ends vs. OS and his solution was (get a 3rd party) pump up and see what settled heights result. I'm not convinced as this doesn't fit a theory where just NSF drops. He did advise that there's a possibility of cascade: unions rusted through that break, new link pipes, rest of the hydragas units as old...

Anyone tried these reconditioned hydrogas units? As the failures are usually the nitrile rubber, are they just replated & re-gassed units with a lifetime as remained on the scrapped vehicle from which they were salvaged?

Cheers
Mike

[Mike63]

It sounds like the membrane has gone. Luckily the NSF is the second least awkward sphere to replace! Have you tried regassed spheres all round? Now could be the moment - the difference is astounding.
You can buy an oil gun on ebay and transfer the hose with adapter. Although you might be better off buying a central heating test pump and adapting that to take the hose-with-adapter.

Charless, tell me more. If my eyes weren't watering under the Truss moron tax I would be shopping already. How long have you had the recon units? Was the visible diaphragm crazed/cracked? Can the rubber be assisted? I'm thinking Wurth Rubber Conditioner. The adapter pipes from the rusted grease gun might be the only salvagable item; but I'm surprised an oil can will get to 400+ psi? There were some high pressure 10mm bore heating systems but I don't expect they ran at such pressures.

My Mini experience suggests a cascade: start with the top wishbone, needs new suspension knuckle, then new needle rollers, new shaft, new seals ...

[Charless]

Hi Mike,
I have had regassed spheres on one for 7 years and even older units on the other for 5 years. The previous units on both cars were OK but low on nitrogen pressure so that the spring element was almost non existent. You should be able to hold each corner (of the car) down and have it spring up with bounces when released. When the nitrogen is depleted there is almost no spring back - like what happens when you encounter bumps when driving! Fluid pressure can compensate the ride height loss but there is increasingly less shock absorption in normal driving because there is less gas and more (non compressible) fluid.
The old diaphragms were not damaged and are never visible (but previously leaked fluid turned to powdery dust can sometimes be seen underneath damaged spheres. Because you can't get to the rubber there is nothing to be done to preserve them.
Oil gun not oil can! You are much better off using a central heating test pump similar to this:-
https://www.amazon.co.uk/Dyna-Living-Pr ... 4464&psc=1
I don't have this brand and both cheaper and more expensive versions are available in various places online. The pressure gauge reads to over 600 psi where you need an absolute maximum of 400psi. Also these seals are designed for holding water at pressure - so more 'designed' than the oil gun type. I have had one of these for years and can recommend this type.
Hope this helps,
Charles