How to: Replace the Hydragas Units and Install Lowering Pins - MG-Rover.org Forums
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post #1 of 27 (permalink) Old 11-03-2009, 15:29 Thread Starter
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How to: Replace the Hydragas Units and Install Lowering Pins

Hydragas Units

The ride quality in my F had become intolerably rough. After advice from this forum I decided to change the main parts responsible for ride quality the hydragas units. Apparently the hydrogen can escape from the top sphere of the unit, and so it loses its ability to compress. When I pressed down on either end of my car, there was very little 'bounce'. There should be several inches of flexibility, instead I had about 1/2 inch.

New ones are hard to find, and I only managed to find new front ones (from eBay, 50 each). For the rear, I settled for low mileage used ones for 30 each.

Part numbers

Trophy

Front: RNK000010
Rear: RPJ100010

Non Trophy

Front: RNK100070
Rear: RPJ100020

Lowering Pins

The MGF looks plain silly when pumped up to Rover's recommended ride height. You can let pressure out yourself and so lower the car for free, but this will compromise your handling, ride quality and the health of the suspension. So I decide to add lowering pins whilst replacing the hydragas units, because you need to do everything up to and including removing the hydragas units in order to install the lowering pins, so I decided to do both at the same time.

Exhibit A. My MGF pumped up to Rover's recommended ride height:



I got my pins from Mike Satur, largely because I couldn't find them anywhere else. You're looking at around 60 including VAT and delivery. You can get 'lowering knuckles' which are a teensy bit easier to fit, but frankly I'd rather do two minutes work than hand over an extra 50. Lowering pins go inside the existing lowering knuckles.




Tools Required

Axle stands (note: I used two pairs so I could do it all at once, but it is perfectly possible to raise one side of the car at a time)
Jack
10mm socket and spanner, 17mm spanner
An empty 2L milk bottle
Someone to repump your hydragas when it's all over (independent hydragas operators from The Hydragas Register are much cheaper than garages and they will often travel to you useful as you won't have any suspension with which to drive to them).


How to Replace Your Hydragas Units and Install Lowering Pins.

Obviously you need to raise the car and remove the road wheels. I'm assuming you don't need a pictorial how-to for that.

Next, you need to depressurise your hydragas system. The valves can be found under the bonnet, and are just like bicycle tyre valves. You simply jab a screwdriver inside and the fluid comes out. It is pressurised to almost 400psi though, so you'd be wise to contrive some sort of protection against the escaping fluid. I chose to make two holes at the top of an empty milk bottle, and stick my screwdriver through to depressurise. Each side seemed to release just over 500ml.









To access the front hydragas units you need to first remove the plastic cowl above the road wheel. These are held in by rubbish plastic screws around the edge mostly. Undo screws and yank out.





Next you will see the brackets holding the hydragas units in place, held in by four 10mm bolts. The two at the bottom attach to the body of the bracket, whereas the two at the top have a nut behind them which you'll need to hold in order to remove the bolt. You also need to remove the cable attached to the bracket, this is done by simply unclipping it from the metal hook.










Now you will see the hydragas unit itself. The only thing holding it in place now is the hydragas valve. You get to this from under the bonnet, and will need a 17mm spanner to undo them.




After that, you just need to lift the unit off of the knuckle and pull it down under the wheel arch. This is a bit tricky, but don't be afraid of using a little force.




This exposes the lowering knuckle:



If you are installing the lowering pins this is where you remove the knuckles. Simply insert a flat screwdriver beneath the orange plastic rim and ease it upwards. Be careful here as the plastic is brittle.





For the rear hydragas units, things are a little more complicated, as access above them is much more restricted. They are again held in by four bolts, but to remove these I had to disconnect the shock absorbers at the bottom (you'll need 13mm and 17mm spanners as I recall), and move the coolant tank out of the way so my arm would fit in (this is held in by two 8mm bolts).





This shows the top of the hydragas unit, just below the two cables.




View of the exposed rear unit. You'll have to use some force to persuade it out.





I struggled to fit my 17mm spanner into the engine bay and turn it at the same time because it was so long, so I used a small adjustable spanner instead. Apart from that the rears are removed in the same way as the front pair.

If you are not installing lowering pins then this is where you put the new units in and put everything back together in reverse order. If you ARE installing them, this is how to put the new pins into the knuckles:

First, remove the spring and washer that sit on top. Then use a screwdriver to prise off the circlip holding the rubber over the shoulder of the pin.




To remove the pin, hold the knuckle in the middle and tap the thin end of the pin onto the floor this should push it out the other side. Insert new pin.



I was somewhat dismayed to see that the MS pins are in fact only 10mm or so shorter than the old ones not sure how this can translate into a 30mm reduction in ride height as advertised!





When you're reassembling, the only tricky bit is getting the circlip back on. I found it easiest to get it over the rubber lip first, then prise them both together down over the shoulder of the pin.


After that, reassembling is very much the reverse of what you've just done. Be sure to tighten the hydragas valves properly you don't want to take everything apart again to fix a leak. Remember that when you pump up the hydragas afterwards you're looking for 369mm (+/- 10mm) ride height, measured from the centre of the wheel to the wheel arch above, or 339mm (+/- 10mm) if you've installed lowering pins.


This is how it all looks afterwards, with a ride height of about 340mm.





The difference made by the new hydragas units is really quite dramatic. I used to bounce over road surfaces like a bag of bolts, but it's much more civilised now. Certainly the best money I've spent on the car so far. The lowering pins make it look a lot cooler too, although for some odd reason the front sits a little higher than the rear.

It's really not that difficult to do once you know what it involves. Certainly worth the 200 saving from taking it to a garage. All in it took me about four hours, but then I'm quite slow at these things and I was stopping to take photos.
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post #2 of 27 (permalink) Old 11-03-2009, 15:50
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What a great thread! Bookmarked for future reference.

Have some rep.

Last edited by MGFNorway; 16-03-2009 at 21:53.
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post #3 of 27 (permalink) Old 11-03-2009, 16:05
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Looks a great job. Well done.

If you did not have a problem with your Hydragas units, would you have still installed lowering pins? reason, I am thinking of having lowering pins on my MGF, but do not have a problem with my Hydragas units.

Do you think it is worth it?

Last edited by Chris T; 12-03-2009 at 20:20. Reason: Quote removed to reduce the size of thread
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post #4 of 27 (permalink) Old 11-03-2009, 16:14
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Great write up

Can you tell me how much flexibility you have in say the front suspension with new units - for example if you push down on the front how far does the car go down?

Did you use a garage to pump the system back up - after using a vacuum pump?

Thanks

chris
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post #5 of 27 (permalink) Old 11-03-2009, 16:21 Thread Starter
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Alan, I was unhappy with the appearance of the car after being pumped up to regulation height. I would still have done it, but you have to factor in the cost of repumping. It was just fortunate for me that both jobs required the same work. It was worth it to me, because I'm much happier with the appearance of the car now. If you're just doing the pins, you're looking at around 100 and an afternoon - not too bad.

Chris - the front end will depress around three inches now, at a guess (I haven't measured). I can measure if you like. I suppose this is a good indicator of hydragas unit health. I contacted a man called Peter Smalley from the Hydragas Register who came round and did it at home for me. And yes he used a vacuum pump.
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post #6 of 27 (permalink) Old 11-03-2009, 16:41
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I Would appreciate it if you could try to get a measure of the deflection of the front suspension as I am trying to judge the health of the Hydragas units

Thanks in advance

Chris
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post #7 of 27 (permalink) Old 12-03-2009, 17:15 Thread Starter
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Okay, my earlier guess was wildly wrong. If I give the rear a firm press down, it depresses by around an inch, and the front closer to two inches. That's an approximation, though, it's hard to measure and bounce at the same time! I presume the rear bounces less because it's under more weight from the engine.
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post #8 of 27 (permalink) Old 12-03-2009, 17:30
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Another great how to - well done. One for Pete's site I thnk
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post #9 of 27 (permalink) Old 12-03-2009, 18:37 Thread Starter
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Ooh, now that is an honour. I do like the idea of actually being able to contribute something useful after leeching off the collective wisdom for so long.
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post #10 of 27 (permalink) Old 12-03-2009, 19:56
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Quote:
Originally Posted by Villager View Post


I was somewhat dismayed to see that the MS pins are in fact only 10mm or so shorter than the old ones not sure how this can translate into a 30mm reduction in ride height as advertised!




The reason for this is because of the leverage ratio that the hydragas unit operates - which is 3:1. I.e. 10mm at the length of lever (the top arm) at the hydragas unit translates to 30mm at the end of the top arm.

Brian.
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post #11 of 27 (permalink) Old 12-03-2009, 20:15 Thread Starter
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Ah, I suspected something like that.. glad you could explain.
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post #12 of 27 (permalink) Old 12-03-2009, 21:44
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Great thread mate. Cheers

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post #13 of 27 (permalink) Old 25-03-2009, 09:15 Thread Starter
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Having driven around a thousand miles since doing this work, on a variety of roads, I thought I'd provide an update:

My area of Manchester is surrounded by speed bumps, some of them ridiculously bulbous. With a ride height of 340mm (ish), I can make it over most of them at a reasonable speed. With the largest ones I have to crawl over them at 5mph or so to avoid scraping the bottom of the car. This is fine, but it also means I wouldn't reduce the ride height any further, even though I would like to take another 10mm off or so to further improve the appearance (and still be more or less within tolerance of the recommended RH). Anyone not surrounded by them will have no problems.

The car does seem to handle better, more direct, but as I changed the hydragas units, lowering pins and dodgy ball joints together I can't pinpoint what is responsible for that.

Ride quality is grealty improved, maybe as much as 60/70% of the bumpiness and rattling caused by uneven roads has been eliminated, which is well worth it in my opinion. I'm enjoying driving the car much more these days
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post #14 of 27 (permalink) Old 31-03-2009, 16:11
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I have already had this done to Purple Haze and would highly recommend it to everyone on the forum
Yes the rear does sit lower than the front likewise with mine but don't forget about the added weight of the engine on the rear which gives that affect
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post #15 of 27 (permalink) Old 31-03-2009, 16:48
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Am i correct in thinking that the lowering pins are trophy parts as the trophy sat 20mm lower
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post #16 of 27 (permalink) Old 31-03-2009, 17:26
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Quote:
Originally Posted by mgf-jordanolly View Post
Am i correct in thinking that the lowering pins are trophy parts as the trophy sat 20mm lower
No, the trophy is lowered by virtue of different hydragas units, there are also different dampers and interconnecting pipes to go with these which stiffen the car quite considerably..

Brian.
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post #17 of 27 (permalink) Old 02-03-2010, 07:44
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fantastic thread
love your work

just 1 question

i cant get the passenger side rear unit out now i have disconnected everything.

does it come out under the wheel arch or out the engine bay ???

(typing with filthy hands, thinking this wouldnt be toooooo hard)


any help appreciated

your HOW TO is with out the best i have seen
thank you so much for getting me this far

PerthMGF
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post #18 of 27 (permalink) Old 02-03-2010, 08:02
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Quote:
Originally Posted by PerthMgf View Post
fantastic thread
love your work

just 1 question

i cant get the passenger side rear unit out now i have disconnected everything.

does it come out under the wheel arch or out the engine bay ???

(typing with filthy hands, thinking this wouldnt be toooooo hard)


any help appreciated

your HOW TO is with out the best i have seen
thank you so much for getting me this far

PerthMGF
Thinking here, A new one for me, where are you supporting with your axle stands, try jacking the body up on that corner.but dont lift the car off the stands.
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post #19 of 27 (permalink) Old 02-03-2010, 09:30
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Its all good now

Thanks for you help
managed to take out ecu and wangle it out.

NOW...... ive fitted the new one but it seems loose after i have attached the 4 bolts to hold it in place

is this normal ????
it is 100% the right part (hydragas part RPJ100020)

any thoughts ???


(and as a side note - does anyone know how to get shocks undone that have a rounded stud/top ??)

thanks again for all your help
appreciated

PerthMGF
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post #20 of 27 (permalink) Old 02-03-2010, 10:38 Thread Starter
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Quote:
Originally Posted by PerthMgf View Post
Its all good now

Thanks for you help
managed to take out ecu and wangle it out.

NOW...... ive fitted the new one but it seems loose after i have attached the 4 bolts to hold it in place

is this normal ????
I was going to say it is awkward you've just go to apply the right balance of wriggling and brute force.

I think mine had a small amount of movement. I can't see how it should matter; they can't go anywhere, and movement shouldn't affect their internal operation. Are the bolts properly tightened, so that the front plate it pressed against the rear?
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