Topic

Hi All
My 2001 F is rather low at the moment, and thinking about what to do has made me realise that I'm a bit ignorant about the hydragas system, so here are a few basic questions...

For info, the current wheel centre to arch measurement is about 325mm. I've had the car since Feb 2014, and have some history which seems to show that the last time it had hydragas fluid added was in 2012 when 1 litre was charged for as part of a routine service. the suspension is not solid, but feels quite stiff, and the car does crash a bit over potholes etc.

Q1... Is there an easy way of knowing if I have lowering knuckles ? Otherwise I don't know if it should be 368mm or lower (338 mm I think is the specified height with lowering knuckles).
The car has 16" wheels, stainless grille, silver vents and console trim, ABS on an MPi etc, and a matching hardtop, so it seems to have had a fair bit in the way of extras specified when new, so I'm wondering if that might also have included lowering knuckles.

Q2 Is there a way of knowing whether I can just get fluid pumped in, or whether the amount of nitrogen left is getting low...is there anything like, for example, the PSI required to achieve the correct height that tells you how empty the gas side is.

Thanks in advance for any light that can be shed.

Hi Bill, you are well under the recommended height of 368mm, and you will be feeling every bump in the road.
The tolerance is +- 10mm.

You need to get this pumped up at the first opportunity, there are plenty of garages in your region that will do this for you. The valves are under the plastic cover in the bonnet area.
Check out the “Hydrogas Register” on google. This will locate the garages in your area that have the pump up equipment to carry this out. Price around £35/£50.00. Cost me £45.00 last time I had mine done.

Regards
David

Thanks David, I do know of 3 places within about 30 miles where I can get fluid pumped in, my problem is though, that if I went to one I wouldn't know whether to tell them to set it to the normal 368 height, or the correct 338mm height for cars with lowering knuckles.

Also I understand that if the problem is that there is not enough gas left in the top sphere then just adding fluid to the lower chamber can result in the gas/fluid separating diaphragm rubbing and getting damaged by the sealing rivet at the top of the gas chamber, which then means the unit can't then be rescued by the method of welding on a valve and adding nitrogen, so that was why I was asking if there's any way of knowing how much gas is left at the moment

Hi Bill,

There is no way of knowing how much gas is left in the spheres, and age isn't a great indication either of how much nitrogen might be left.

Back in the spring I installed four of my regassed spheres into a 2001 Steptronic, which had an extremely harsh ride. The regassed spheres transformed the ride; it now floats over bumps. The four spheres I removed had all failed inside; each one was hydro-locked (full of water where there should have been nitrogen). This car had around 60,000 miles on the odometer.

I've also installed four regassed spheres into a 1996 MGF. Three of the four spheres that were removed had failed: two were leaking fluid from the bottom, and one had no nitrogen at the top. Another 1996 F also had three of the four spheres fail (two at the bottom, one at the top). Oddly both of these Fs were Japan export cars and low mileage; under 100,000 km on either one of them.

This past weekend I installed a set of regassed spheres in a 1996 MGF (~130,000 km on the odometer). This car has had to have its ride height adjusted every year for the four years it has been in Canada. The four spheres that I removed all had nitrogen pressure in the top as evident from the rush of nitrogen that came out as I drill a hole into the top portion. Much more of a 'pssst' sound came from the front two than the back two.

Both of our 1995 MGFs ride quite well; the ride is a bit harsh, but not bad. My wife's F has ~85,000 miles on it, mine ~120,000 miles. I will be installing a set of my regassed spheres into my wife's F this winter and my F next spring.

Interesting to note that I have not had to adjust the ride height of my F in five years and my wife's only once in the past four years.

Mark

Thanks Mark, that seems quite a high failure rate for the spheres you've replaced. I'm hoping mine are OK, I haven't seen any fluid leaks, and there is some movement at least at each corner of the car.

When you re-gas spheres how do you get the right amount of gas in ? Do you gas them up to a given pressure before putting any fluid at all into the lower chamber... I'm just wondering if I sent my units away to have valves installed how I would get the suspension properly set up when it was re-assembled. It seems to me that it might be possible to end up with, say, more gas and less fluid in the front, and more fluid and less gas in the rear, and with the two units interconnected you'd still get a similar amount of static springiness at each end, but the response over real bumps when the car was moving could be quite different ? Having said that it does seem as though my car has probably not had too much fluid added as yet, so maybe I should just go for a conventional fluid pump up and see how it feels.

I guess it should be possible to measure the distance from the bottom of the cone to the top of the suspension arm to know whether I've got standard or lowering knuckles, but I don't know what either measurement would be.

Bill wrote: wrote:

Thanks Mark, that seems quite a high failure rate for the spheres you've replaced. I'm hoping mine are OK, I haven't seen any fluid leaks, and there is some movement at least at each corner of the car.

When you re-gas spheres how do you get the right amount of gas in ? Do you gas them up to a given pressure before putting any fluid at all into the lower chamber... I'm just wondering if I sent my units away to have valves installed how I would get the suspension properly set up when it was re-assembled. It seems to me that it might be possible to end up with, say, more gas and less fluid in the front, and more fluid and less gas in the rear, and with the two units interconnected you'd still get a similar amount of static springiness at each end, but the response over real bumps when the car was moving could be quite different ? Having said that it does seem as though my car has probably not had too much fluid added as yet, so maybe I should just go for a conventional fluid pump up and see how it feels.

I guess it should be possible to measure the distance from the bottom of the cone to the top of the suspension arm to know whether I've got standard or lowering knuckles, but I don't know what either measurement would be.

If you have it pumped up to 400psi with hydrolastic fluid if it is standard it should measure arround the 368mm mark, I don't know of any way to check for lowering pins, but I do know 400 psi is the operating pressure and mine is 360mm at that pressure.

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Thanks Steve, that makes sense as when it's at the correct pressure the correct number of square inches area of the cones will be against the lower diaphragm to balance the weight, I think I'm starting to understand it all a bit better now. A good reason to make sure that it's pumped up using an accurate pressure gauge.

Bill,

Actually the failure rate hasn’t been that high. Out of 49 spheres, 38 have been good and only 11 have failed. And of the ones that have fail, 7 rears and 4 fronts.

I regas the spheres at my work bench to the factory specification of 16.55 bar (240 psig), +/-10%. I guess if the nitrogen pressure was way off-spec on two spheres, you could get an uneven distribution of fluid front to rear.

Thanks everyone. I think what I'll do is get a fluid pump up, initially to 400 psi and see if the height is nearest to 338mm or 368mm and ask for the fluid pressure to be fine tuned to whichever of those heights it is, I've still got a picture from when I bought the car in 2014, and it doesn't look all that much higher than it is now, so I think there is a possibility that it will turn out to have the lowering knuckles and need to be 338mm.

I'll see about getting the valves fitted to regas the spheres at a more convenient date, or maybe get a spare ebay set so I can clean and paint them as well etc without the car being OTR for too long.