Servicing your hydrolastic suspension. Or how to give it a deep spring clean!

By Peter Laidler.

As many of you hydro forumers know by now, I’ve been setting about my slightly leaky and rickety hydrolastic system and in doing so, have been learning the true worth, facts and total fallacies of the system. You already know my views to that while some of the bits are worthy – and I put it no higher than that, the rest can only be described as a frill – if not a direct fraud. But be that as it may, it’s what we’ve got. So I’ll stop there.

As a result of a couple of articles and subsequent comments and discussions among the forum flock, and a couple of MCR readers I’ve been asked if there’s anything you can do to ‘maintain’ this what should be a maintenance free system. So I thought……, and really, what I’ve been doing over the past autumn and winter has been JUST that. A bit of maintenance or what you might call ‘spring cleaning’. But better still, it’s been pretty cheap spring cleaning to boot. The problem is that just the mere mention the word ‘hydrolastic’ seems to put the fear of god in the average hydro owner. But help is at hand…………

I found it simplicity itself to de-pressurise the displacers one side at a time using the safe and cheap hose-and-plunger tool I suggest in an earlier article of a few months ago. More expensive and complicated alternatives are available of course! Suspension down and fluid collected it’s a bit of a chore to remove the hydro units, especially the front but just set a nice sunny Saturday afternoon aside, get a cup of coffee handy and set about them. stands ready and safety always in mind too and we’re away. Can I also suggest that you go to Waitrose and get yourself a box of 100 white latex gloves for a fiver and take your wrist watch off too! Life is going to get a) dirtier and b) watch glass scratching too – and expensive when it’s an Omega!

With both displacers removed from the hydrolastic interconnecting pipe (the HIP hereafter), with the Schrader valve removed I was able to flush the pipe through the HIP using a hose adaptor (described below and available from your friendly PIRTEK hydraulic hose supplier). So let’s stop here for a break and chat about this little two part gadget shown in the following pictures..

The gadget is made from two parts. The longer nozzle, PIRTEK part FEMALE SWIVEL 801-06-06 which you can see we’ve sleeved to take a larger diameter garden hose to flush out the HIP. Add to that part PIRTEK part MALE BSP TO METRIC GE-10LR3/8 and you can connect the female swivel to the hydro units to fill them with mains water pressure. Or add a schrader valve insert sweated into the top of the swivel as shown and you can inflate the units to 70psi or so. Either way you can test for leaks. But a word of caution. In the I acquired the BSP male thread was a tight fit into the female thread inside the hydro pipe nut. But a quick spin in the lathe and take the tips off the threads off with a file and it was perfect. If you want me to do yours, just send it with a fiver for the jiffy bag and return post and I’ll send it back by return.

Several photos show the make-up of this little gadget and make its use pretty well self explanatory.

We modified our gadget by sliding a plastic sleeve over the shaft so that it’d accept a standard size garden hose. We also sweated into the shaft a Schrader valve cut from an old tyre valve. With the valve fitted you can inflate the units with air to test for leaks.

Remove the valve and you can attach a hose to inflate the units with water and/or flush the HIP through.

With the metric end of the double ended male adaptor you can attach the 3/8 BSP end to the hydro units.

Remove the adaptor and you can screw the female ended hose adaptor

to the HIP for a simply flush through.

2 minutes of flushing the HIP with clean water from front to rear and out onto the drive was all that was required. But prepare yourself for the pure sewage that’s going to emerge. As for the displacers, a similar ploy was tried. This time we just filled up the displacers with a jug of hot soapy water through the tube opening and a home made funnel and shook the living daylights out of them until they were full. Emptied and repeated the operation time and time and time……… and time………. and time again until the fresh water came out clean. Please persevere here….., each unit contains TWO chambers via a small useless-by-now valve. There’s no quick way and you’re going to be amazed and surprised at the amount of shi……, er……, clag and rusty gunge like sewage that is going to come out. This is the stuff that you DON’T want, believe me. Finally I got a long and narrow bit of plastic pipe and pushed I down the hose and then put the end into the Mr Henry vacuum pipe and turned it on to suck the dregs and remaining liquid out. Yes, maybe a bit OTT and I dare say that leaving the units upside down, pipe downwards overnight would do the same job of fully emptying them. That’s your displacers cleaned out too.

If you’re game and confident………..While the units are out and dry remove the rubber protective end caps (21A1496) and smear the inside of the caps AND the pliable rubber diaphragm with rubber grease or silicon spray. Go on…., slap it on….. Now’s the time to pull the steel cup that supports the dowel 21A1704 and strut 21A1805 away from its round dovetail socket in the diaphragm. Go on….., wiggle it around and pull it out.

The dowel cup twisted free of the diaphragm, the cup with the dowel and the cover

There’s two things you can do now, a) ; Pull the dowel from the cup and thoroughly clean out the hole (it’s 1/2” diameter) with a drill bit or length of wood wrapped in some emery cloth. Now thoroughly grease that hole with coppaslip and b); grease the whole diaphragm and exterior of the cup with rubber grease……, go on, slather it on, it won’t do it any harm. To re-fix the cup thingy to the diaphragm, the simplest way is to slightly inflate the hydro bag with a tyre pump (or water pressure) on the gadget as shown. Then, being greasy and slippery the cup will slip back into place like a well worn sea- boot. Now release the air pressure. Alternatively wait until you have filled up the unit and stoppered the end (see next para.) and wiggle the greased cup back into the round dovetail seating. Removing and replacing this cup from the unit has terrified people in the past. Don’t let it frighten you!

Assembly and refilling. With my new tub of Hydro fluid I carefully filled each hydro unit, shaking and topping up again and again until each was absolutely full, I knocked a hardwood bung into the open end and stored them hoses upright. A simple wood dowel knocked into the hydro units and rear end of the hydro pipe. Simple to shape from a piece of dowel wood using a sharp knife as though sharpening a pencil.

Then I did something similar to the HIP. This time, pal Andy carefully filled up the pipe from the front while I monitored the rear. Before you start filling, go to Boots the Chemist and get a cheapo pack of dental ‘interdental brushes’ and scrub out the Schrader valve part (13H1705) and the interconnecting pipe elbow (21A1519) on the rear sub frame and replace the Schrader valve with a new one OR replace the whole screw-in valve assembly (£15 per x2, EBay, MGRoverspares). Place a clean container beneath the outlet pipe to collect the new, clean fluid that you’ve let run through. And when the neat fresh hydro fluid that’s replaced the air in the pipe comes through, just knock in another wooden plug or bung onto the rear end. That’s all you need to do for now because the HIP is full of new fresh clean hydro fluid.

Now you have a front and rear displacer units and the HIP full of new, clean fresh hydro fluid. Neat, fresh, clean and to the spec required and not the diluted liquid sewage that you’ve drained out. That’s more than you can say about the crap and filthy gungy sewage that’s being pumped into your system from a garage hydro bilge pump that’s been used in and out of every man and his dogs hydro system. All you have to do is to join them back up without getting air into the system.

Time to join the dots. Having greased up the hydro unit jointing threads and nuts, insert the front unit into the sub frame after making sure that you have power hosed or thoroughly washed out and greased up the subframe tower housing with a goodly spray of supertrol 001. The hydro unit ain’t going to leak because there’s a wooden bung in the end of the hose. While you align/position the displacer hose nut to the pipe male thread just pull out the wood or rubber plug and start the thread. There won’t be a problem because it’s a) greased up with coppaslip and b) you only took it apart a few hours(?) ago. Now tighten it up. There….., an air and fluid tight high pressure (?) hydraulic joint.

One of the big failings of the Mini hydro system is the long loop of the rubber front hydro pipe to the joint. You think that by evacuating the system from new or dry, using the cabinet, it will evacuate all the air from this high point. Think again. Most of it but definitely NOT all of it and air ALWAYS gathers at this high point – it’s a law of physics. But now you have. As for the male and female threaded joint. Don’t go ballistic…… the fluid joint is within the male and female tapers. And in the world of pressure, the hydrolastic system is at the bottom of the hydraulic Richter scale, believe me!

The rear is virtually the same procedure as the front. But before you insert and lock in the hydro displacer after thoroughly power washing, cleaning and greasing up the sub frame with Supertrol 001, here’s a tip. Get the flexi- nozzle of the Supertrol can and wiggle it into all the little openings and corners that disappear into a black void, deep in the bowels of the double skinned parts of the sub frame. Now get your spanners ready while you align the male and female joints. Same again but be prepared to get a bit wetter. Grease up the male and female threads with coppaslip, quickly remove the wooden plug so that the female can slip neatly onto the male - just like your mates always told you was best…… and tighten up. At this point you can start to assemble the associated parts such as the struts, dowels, boots, new knuckles and anything else you can think of that needs doing while it’s down because that’s it….., it really is that easy! You have a depressurised air free system just waiting to be pressurised.

If, like me you are only blessed with a small hand operated grease gun type unit (available on EBay, see ‘littletool under hydrolastic for about £60 or so), here’s a few tips. But let me say, it’s served me faultlessly and well for 10 years so far 1) Drill a small hole around the top edge and put a big key ring through it. You can use this to hang the pump from the garage roof without spilling (too much…!) fluid and you can leave it while you have a brew. 2) Lightly screw the Schrader adaptor from the pump onto the new valve on the sub frame and then pump the handle. When you see hydro fluid weeping and dripping from the threaded joint, THEN tighten it. This will ensure that you’re only pumping new fluid into your newly filled hydro system and NOT air. 3) Keeping an eye on the fluid in the pump, keep pumping and look for any weeping from the hydro hose-to-pipe joints and nip up if necessary. It only takes a couple of fills to pressurise and raise the . 4) If you have collected some spilled fluid or fluid that you’ve caught while topping up the units or pipes then feel free to use it if there’s a fair amount but ONLY after you have filtered it through a coffee filter cheap from Tesco and NOT through a bit of cloth 5) Make sure that all the threads, the holes in the struts and cups, the dowels plus the internal strut springs are smeared in coppa-slip ready for the future. Make sure that you check, inspect and replace/repair anything that’s get- attable while the suspension is lowered.

While the hand pump has a pressure gauge it isn’t really relevant to our application. Mechanically, the best option for the operation of our front drive train is when the drive shafts are parallel. I realise that some of the ‘experts’ say otherwise, but that’s my opinion based on good mechanical engineering experience gleaned since Pontius was a pilot. You’ll need to check it again in a week or so because things are going to settle. While you’re down there – as the actress said to the bishop - you could sort out those nasty clonking knuckle joints or at the very least you must replace and grease-up the nylon cups. Also it’s time to check-out the rear helper spring mounts on the radius arms. Do you need to sleeve/bush the actual pin? Replace the knackered oil soaked felt washers? What about replacing the circlips with a far more reliable ‘R’ clips. It’s a simple drill through while the radius arms are lowered

The bits you’re going to need BEFORE you start. Copy this article and keep it handy, on your bench Workshop tools and spanners of course, A tub of new Hydro fluid, Boots ‘interdental brushes’ to brush out and clean the Schrader valve seatings, A couple of new Schrader valves free from your local tyre centre OR new valve assemblies (£15 per pair from MGRover spares on Ebay) Box of Tesco cheap one-way-trip coffee filters Tub of Coppaslip and a tub of rubber grease/spray can of silicon grease Large spray can of Supertrol 001 grease – I swear by it

I browsed through this essay trying to think of how to simplify it but the practice really is as simple it reads.

Peter Laidler.