Ride heigh woes after new hydragas spheres

[eumecon]

Hello everyone. I'm hoping for some expertise on what I assume must be a problem others have struggled with. Sorry for the long post!

I had a leak from one of my rear hydragas spheres so took the plunge and replaced all 4 with a set of refurbished ones, plus a set of lowering knuckles from Mike Satur as I really didn't like the idea of cutting my nice new spheres... everything went fine until I went to pump the system back up. I just cannot get the fronts anywhere near the 338mm I expected. Best so far is about 320mm even at 520psi.

First disclaimer, yes I am using one of the grease type pumps and I know this is like amateur hour. But where I live in Germany, hydragas filling is not so easy to come by. I know a garage not far away with a liquid levers pump but they charged me €120 just to top up the suspension once so have been trying to avoid taking it there up to now...

The reasons I came up with for not getting the ride height:

- something wrong with the hydragas spheres or they are the incorrect ones (i.e. trophy or already cut) - maybe they are all defective somehow but I think at least they are original ride height ones as I checked the length of the piston against one of my old spheres (unless these were also lowered ones but I doubt it. I remember it coming back from an MG specialist who did a service years ago and it was sitting sky high). I measured the height of the piston from the sphere at 14mm.

- Something completely mis-engineered in the lowering knuckles or somehow I have fitted them or the spheres wrong

- the gauge on my grease gun pump is way, way off.

- big airlocks on both sides which I guess is the most likely cause. I tried multiple ways to evacuate air out of the system though including pumping it over pressure then draining it, and using a vacuum pump on the drain port of the grease gun (via a fluid catcher) to evacuate everything out before re-pumping. I must have re-pumped both sides at least 10 times in my endeavours to get rid of leaks. I'm not 100% sure how well the vacuuming works, it did get a jam jar full of fluid out after de-pressurising but there was still fluid in the tube from the schrader valve which wasn't budging after 20 minutes on the vacuum pump.

I find it a bit strange both sides are equally bad in terms of height but that does not rule out any of the above I guess.

From reading previous forums I realised one potential issue was my MGF was not using any spacers - from what I understand (?) there are usually 3.6mm on the front and 2.3mm on the rear. As the rear is way lower than the front I fitted some 3.6mm to the rear to at least even it up but the best I can get out the back is 310mm even with the spacers, again at 520psi. At about 400psi they are still 300mm barely off the bump stops.

Anyway, the next step is to admit defeat and take to the place with the liquid levers pump. They used to be an MG Rover dealer so hopefully they have the experience to sort it out. Before that I want to get some proper hydrolastic fluid to fill it with though. I'm using pure green BASF G48 coolant at the moment and I don't want them refusing to touch it because of that.

So, gives me an excuse to drain and refill the system one more time.... I might also disconnect the rear spheres and see if the lines flush through properly, and then I can properly driain them and fill as much as I can with correct fluid. Maybe by some miracle it works this time.

Anyway, to the questions....

- Is it better to let the car sink to the ground with a completely drained system and fill from there or support it while it was drained? Everytime I drained it so far I supported the weight of the car for fear of it damaging the spheres but maybe that's the only way to get it right? I thought the ideal way to do it was to have it up on axle stands with the wheels off, then jack the suspension on both front and rear to correct rider height and commence pumping until i can see it is now slightly off the chassis jack stands - this seemed to work and they were sitting at 340mm but then when back on the ground it was down to 310mm!
- With a completely empty system is there any foolproof method to fill without airlocks (better to fill spheres in advance or vacuum in advance?)
- Are people commonly using spacers? It seems a bit counter intuitive to use them on something with lowering knuckles
- Does anyone know how much fluid exactly (or even roughly) it takes to get the system to correct ride height at 400psi?

Thanks in advance

[Rob Bell]

Wow, this is tricky... but good questions!

- Is it better to let the car sink to the ground with a completely drained system and fill from there or support it while it was drained? Everytime I drained it so far I supported the weight of the car for fear of it damaging the spheres but maybe that's the only way to get it right? I thought the ideal way to do it was to have it up on axle stands with the wheels off, then jack the suspension on both front and rear to correct rider height and commence pumping until i can see it is now slightly off the chassis jack stands - this seemed to work and they were sitting at 340mm but then when back on the ground it was down to 310mm!

Ideally, you need a pump that can vacuum the system to remove any entrapped air. Obviously, the grease-gun type pump cannot do this, but there is nothing fundamentally wrong with this pumps. They may just need a little more preparation in terms of pre-filling the displacers and the inconnecting hydraulic lines before attempting to pressurise. I would usually fill the invidual spheres as best as possible with fluid (may be with a syringe?) before connecting the hydraulic line and ensure that the hydraulic line is pre-filled (a couple of strokes of the pump before connecting the rear spheres for example).

To your specific question, filling then draining the system so the car is practically on the deck may be a good way of removing some entrapped air. You won't damage the spheres doing this (or rather, I have not damaged mine doing this!)

I always raise the car with the wheels on the ground and the suspension under full vehicle weight.

The final height of the system will depend on the knuckles - they are usually supplied unassembled these days, without the nylon bearing surfaces - but I guess you've build them up correctly? Assuming that the displacer cones have not been shortened (it would be unusual for this, as it was not the commonest way of lowering cars back in the day), then 400psi should get you 340mm of ride height (as measured between the wheel centre and the wheel arch lip vertically above).

How accurate is your pressure gauge do you think? Might be worth checking in case the fluid is not at the pressure you think it is...?

- With a completely empty system is there any foolproof method to fill without airlocks (better to fill spheres in advance or vacuum in advance?)

See answer above - pre-fill everything to the best of your ability first. Or use a vacuum pump, but I know you don't have access to this.

- Are people commonly using spacers? It seems a bit counter intuitive to use them on something with lowering knuckles

I suspect that the knuckles are designed to be used with the standard spacers. They can also be used to trim the final ride height. 3.2 and 2.3mm front and rear sounds about right. The spacer may have another function of spreading the load from the steel knuckle to the alloy displacer cone. I'd keep them.

- Does anyone know how much fluid exactly (or even roughly) it takes to get the system to correct ride height at 400psi?

You know, I've never measured that. I would guestimate that each sphere takes at least 500ml of fluid, plus you must have approximately another litre in the hydraulic line (should be easy enough to work out if you know the internal diameter of the pipe and its length). So approximately 2 litres per side?

[Charless]

Broadly agree about total fluid, between 2 and 3 litres in my experience but only a ballpark guesstimate looking at what remains in a 5l container.
I think the air exclusion can be done if, as Rob recommends, you don't try and lift the car on jacks to make the pumping less arduous - it prevents the car sinking to the bump stops which is what expels the air. I have been advised by an/the expert in the hydragas and hydralastic (yes there is a difference!) field that to remove all significant remaining air you only need to pump both sides up and then (controlled) release the pressure with the car on the ground. Any remaining air is dispelled before the last of the fluid as it settles to the bump stops. You can then repump to pressure. I have never needed to go beyond 400 psi to achieve the correct height with a dozen different Fs.
I would think it unlikely that your pressure gauge is reading incorrectly, so air would be my bet as to why you can't get the height. It also seems a good check to remove the rear unions and prove that fluid is pumping through unchecked from the filling valves. At which point you could pre fill the rear spheres with fluid an Rob says.
There are various people offering reconditioned spheres. I have never needed to look elsewhere than Ian and Dawn Kennedy:-
https://hahsltd.co.uk/
who do the regassing valve on each sphere. If you have this type; some garages and A/C outlets could check your nitrogen gas pressures. It might be that Customs or some other Health and Safety freaks released all the gas for international transit. I hope you find the answer (and let us know!).
Good Luck,
Charles

[eumecon]

Thanks both for the encouraging answers! I'm going to take another look at this at the weekend.

I did prefill the spheres (reconditioned from a UK MGF supplier, I can't remember which currently) with a syringe but didn't flush through the lines. I will definitely try this and also filling the car while it is completely sunk to the ground.

The final height of the system will depend on the knuckles - they are usually supplied unassembled these days, without the nylon bearing surfaces - but I guess you've build them up correctly?

How accurate is your pressure gauge do you think? Might be worth checking in case the fluid is not at the pressure you think it is...?

Hmm I can't see how you can really go wrong with the knuckles (famous last words) the are just the knuckle itself and a receiving cup to go underneath. If anything I would assume misfitment would cause too high a ride height.

I would hope the gauge is accurate.. but have no real idea. If I get nowhere further this weekend at least I know it will have proper fluid in it and can take it to somewhere with another pump to verify.

[Reckless Rat]

On a standard MGF the rear spheres ARE different from the front ones, due to the higher loading at the rear. In this photo the front one is on the left with a rear one next to it - you can see that the part where the knuckles fits is much shorter on the front sphere than on the rear, and the bases are different diameters. Might be worth checking.

[eumecon]

On a standard MGF the rear spheres ARE different from the front ones, due to the higher loading at the rear. In this photo the front one is on the left with a rear one next to it - you can see that the part where the knuckles fits is much shorter on the front sphere than on the rear, and the bases are different diameters. Might be worth checking.

I knew the rear was different to the front but not in the piston length also, interesting. I'll double check this too

[eumecon]

So... I don't know about progress as the car is in pieces again but I guess we might be getting somewhere...

I drained the system with the car on the ground after driving around and refilled it just to see if it would make much difference but at an indicated 400psi, the car was barely off the bump stops with a ride height of 300mm. There didn't seem to be any air coming out at all, just fluid so I'm not convinced there is still an airlock.

So I decided to get it up on axle stands, strip all the spheres out and start from scratch with the proper fluid rather than the pure coolant I've been using.

First thing I noticed when I took the front wheel off - even with the system still at an indicated 400psi the sphere was not toucing the ridge of the knuckle, it was about 15mm higher up



I wondered if this was normal with no weight on the wheels but seems a bit odd so I am beinging to conclude my gauge is crap and 400psi is actually nowhere near, or maybe I am not reading it properly. I thought you had to take the pressure reading while pressing the leaver pressed in as that is when the system is open but maybe not.

On the other side however I found another issue so glad I took the spheres off. When I depressurised the left side one of the knuckles came out so I guess it wasn't seating properly. They generally don't seem to take too much pressure to go into the lower arm recess so were a point of concern.



Well at least I am getting quick at stripping the spheres out I can't see any major issues with the new spheres and they don't look as if they have been cut and the right ones were fitted in the right places.

Flushed some fluid through the lines. They don't seem to be blocked.

For the sake of €7 I've ordered a new 600psi gauge So the plan is now to fit the front spacers, fill the spheres with proper hydragas fluid using a syringe and flush through the lines again, and try pumping up when it is back on the ground a couple of times then get it to ride height regarless of the displayed pressure (assuming the new gauge doesn't help). If it is way over 400psi I'll still take it to the place with the liquid levers pump and get them to double check it.

[Reckless Rat]

I made up my own hydragas fluid, using green antifreeze diluted by 1:1 with water and then an equal part of alcohol added. Works fine. The alcohol is 90% ethanol with 10% methanol, off the supermarket shelves here in France. Not recommended even for the hardiest of street drinkers, but OK in an MGF.

While you're at it, treat yourself to some '0' rings for your little pump. They don't last very long due to the sliding action and if they are knackered you'll be pumping yourself silly. You can reduce air ingress by having someone give gentle pressure to the pump while you screw the union on to the hydragas valve.

I never look at the gauge on the pump. If you're doing it right the car should start to rise (albeit very slowly) as soon as you start getting fluid into the system. Keep a supply handy to top the pump up as you proceed.

[RobboMC]

Back when I had Hydragas and the DIY pump I would jack the wheels off the ground ( one side only of course )
or at least take the weight off the wheels; when pumping liquid in. That way you're not pumping the weight of the car with your little pump.

A neat trick is to jack the car up to the desired height, with wheels resting on the ground,
then pump liquid in, when the pumping action gets hard the wheels are taking the weight and that gets the height quote close first time.


And +1 to replacing the O-ring in the pump every year or two. They cost a few cents and the inconvenience of O-Ring failure is great.

[eumecon]

Thanks for all the ideas. Well, after the escapades of taking all the suspension apart and back together again I have achieved some success! On one side....

I used the following method to fill from empty, given I had access to a vacuum pump and the hydragas pump had the optional drain valve (I know problably takes longer that pre-filling the spheres, but I figured this would be the foolproof method... ha!) :

-Have the car up on axle stands
-Jack up the front and rear hubs to just below the desired ride height (in my case 33cm)
-Open the low loss connector and pump the system down with the vacuum pump, which also sucks all the old fluid out the lines. Close the vavel on the grease gun and the low loss connector, at this point there shuold only be a vacuum in the line from the pump to the low loss connector.
-Fill the gun and start pumping until you feel pressure and/or it starts jumping in pressure on the gauge. At this point I'd put in around 600ml of fluid
-Keep pumping while whatching the axle stands, at soon as it starts to move off the axle stands you know you are getting close, at which point lower the jacks (at this point, about 850ml, and the pump is showing around 400psi

But then in my experience this isn't enough. Even though it was measuring with the jack under the hub a front ride height of 340mm. When you actually drop the car on the ground it loses around 2cm... so back to pumping. To get back to the 340mm I had to pump in another 400ml or so and up to a pressure of 520psi.

And heres where it gets weird.... I did the left side first, then once I did the right side I went back and double checked the left, and now it was 350mm So ended up draining about 200ml back out to get it back to the same side on the left.

So. No idea what that is about but to get to 340mm the right is now at 520psi and the left 450... ok time I stopped looking at the gauge

I guess the right might still have some airlock somehow, as the rear is still lower on the right than the left... so I'll try draining down and re-filling it... one last time....

[Rob Bell]

To be honest, the official workshop manual simply advises on a final ride height and not a hydraulic line pressure. It is only experience that tells us that standard height with an unmodified suspension = 400psi. Lowering knuckles generally give a ride height of 340mm at the same pressure.

It's been quite a phaff so far, but I hope you crack this problem soon

[eumecon]

Thanks, well I think I've sorted it enough for the moment. Tried draining and refilling the right side and then noticed the left side seemed to have settled down and was riding lower... anyway both fronts now at 340mm with right showing something like 520psi and the left 450... but I also have decided to ignore the gauge

Looking at what I have left over in my 5 litre hydragas bottle, it seems each side took just over 1.5l to fill get to this ride height. Sounds like its in the same ballpark as what was guessed. I suppose it dpeends on how much nitrogen has leaked out of the spheres and having to compensate there.

The rears are still lower, something like 320mm even with the wider spacers. But I'll drive it around and see if it evens out a bit. Got bigger concerns now, while removing the hydragas lines from the rear I noticed the expansion tank is full of mayonaise. It never ends!

[Rob Bell]

Oh no!!! That doesn't sound good.

You will likely need to lift the head and change the gasket at a minimum if you've got just the custard in there. If only a slight slick, then may be you're lucky - I'll keep my fingers crossed!!!