The MGF Register Forums

Does anybody have any advice, method, how to video etc. regarding the replaced a front nearside hydragas sphere, as mine recently emptied its contents all over the drive. I have a replacement and had a mobile mechanic lined up, him thinking it would be a quick and easy job (I've even borrowed a pump and acquired some fluid). Having had a closer look, we're talking subframe and brake servo removal. Is this right of is there an easier method?
Thanks

Doable without removing subframe. Not done it myself, but had Hydragas And Hydrolastic Service Ltd change all the spheres on my Trophy and they didn't need to drop the subframe.

It isn't too difficult Steve.
Remove the closing panel (black plastic cover under the bonnet) to access the schrader valve fill point, depressurise any remaining LH side hydragas while on the ground.
Jack up the front (central jacking point) and remove NSF wheel (having previously loosened wheelnuts while on the ground). Axle stands under subframe.
Unscrew 17mm union nut on sphere and remove the four 10mm bolts on the 'retaining plate' which holds the sphere in place.
Wrangle the sphere out without damaging the 'roller foot joint' (pin set in plastic on which the sphere sits).
Clean out road dirt and lightly grease and/or paint metal parts to go back in.
Wrangle in the new sphere ensuring no damage to roller foot joint (which is handed).
Re attach union nut loosely and replace the retaining plate holding the sphere in. When it is all solid tighten the union nut to 20 Nm.
Pump up system while still jacked up and check for leaks.
Refit wheel and lower the jack. Allow the fluid to depressurise into the pump - this removes any air before the last of the fluid is expelled. Now pump the hydragas fluid up to the correct height. 368mm @ 17degrees C from centre of front wheel vertically to wheel arch. Good time to check the other side before you put the pump away!
A hinged 17mm spanner like this will help immensely for the union nut:-

A 1/4 in drive "Crowfoot" Spanner from Snap-On is useful.
Geoff.F

Thanks Charles & Geoff,

Am I right in assuming that the sphere is removed out through the front wheel arch??

Yes, once the hydragas is depressured and the subframe supported, there is 'plenty of' room to manouvre it out by depressing the hub. There is no need to remove the inner arch liner.
The turret or retaining plate bolts can be very awkward as they haven't moved since the factory when they were assembled dry with an air gun. Two of them have captive nuts, the other two need two sockets or ring spanners to get moving without rounding them off. Needless to say grease them well before reassembly.
The OSF sphere is the most accessible of all, the rears are much harder to access; so NSF is a good starter!

Thanks both!

Thanks for the in-depth instructions Charles. Job has been done today and car now sits square and is ready to go!

Good news, glad to be of assistance! See you at MGF 25+1!

Hi, new to this forum but have a related question if that is ok. I was just wondering if you should replace spheres in pairs to keep everything balanced. Just got a 1997 car which is in great shape but keeps dropping on the driver side so I think one of the spheres is dead. I think it is front so going to replace but should I do both fronts at the same time.

The spheres are connected front and rear on each side so it makes sense to replace both the lefts or both the rights at the same time;
but as you suggest to keeping a left-right balance is also important, the end result is that
after 20+ years you really should replace all four at once to maintain a proper balance in the car.

I would only replace what is damaged*. All spheres (even new unused ones) are at least 20 years old and have a service life which I believe was designed to be 15 years. All of them are well beyond this now, though these have proved extremely tough and well designed components.
The best answer* is refurbished (regassed and tested by specialist suppliers) units all round, but they will still be at least 20 years old and failures tend to be irreversible if and when they occur (pretty much what Robbo above is suggesting).
Everyone who has fitted 4 regassed spheres says the difference in ride quality was unbelievably good - as the cars were originally. But that costs perhaps more money than you want to spend just now!
I would definitely establish what is actually broken first, before deciding on options, it might only be a hydragas pipe which is leaking and not the spheres. Check for signs of leaking underneath.

Personally I would go the regassing route for all 4 spheres. In my view the amount of gas left in the spheres will have reduced considerably over the years so the ride will be harder than it should be. It's better to do the job sooner rather than later so that you get the full benefit for years to come. I had all 4 replaced on my MGF last year and no regrets. I used Hydragas and Hydrolastic Service Ltd (www.hahsltd.co.uk) but there other companies you could consider.

Charless wrote: ↑

Mon Nov 07, 2022 10:49 am

I would definitely establish what is actually broken first, before deciding on options, it might only be a hydragas pipe which is leaking and not the spheres. Check for signs of leaking underneath.

I am as wondering about this, can't see any really obvious leaks, but it was a bit odd as I pumped it all up, it held pressure fine but then drove it just a few miles and it sagged again. I would have expected a pipe to just leak right away, with 3-400psi i would not expect it to hold this at all if there was a leak. So not really sure what is going on. Have pumped it up again and it is holding on the drive but got a brake issue to sort before I can test to see if it drops again after a short drive.

It might be that when you hit road bumps the 400 psi is momentarily increased above the leak threshold so that it squirts out a tiny amount of fluid past the breach which then reseals at normal pressure. This could be fluid into the gas section of a sphere so that nothing shows on the outside.

Piccy helps:



Remember the front and rear hydragas spheres are different - don't mix them up! In this photo the top left one is a front sphere and the one to its right is a rear one - the displacer cones are different legths and the skirts on the spheres are different diameters too.



Expect the suspension knuckle to self destruct when you remove the sphere. The plastic is very brittle when its old. Replace like for like.

Plus, there is no need whatsoever to remove either the brake servo or the subframe. You do have to remove the damper (and you need to prevent the piston rod from turning while you undo the top mount - either with a strap wrench on the outer shield or by holding the top of the piston rod with an adjustable spanner on the flat), but once the system has been depressurised it's an easy job to disconnect the hydragas connection to the sphere and then the 4 bolts that locate the outer casing of the sphere support. The Sphere will then just lift out. Ideally you should remove the inner wing plastic shield for better access.

Don't mix the dampers front - rear either because they have different damping rates. The ones for the MGF are specific and only work on rebound - the bump damping is done by the valves in the sphere itself, so if you are changing them make sure they are the right ones. The TF ones are different and are bi-directional.