Before I can put the engine back in, I need to replace the hydraulic piping. And if I'm going to do that, I might as well take the opportunity to rebuild the front height corrector.
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A DS height corrector
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The purpose of the height correctors (there is also one at the back of the car) is to maintain a given road height under any static load. 'Static' is important, as the height correctors play no role (in the correction of height) when the car is travelling at speed over bumps - the movements are too brief for the height corrector to react and operate.
How It Works
The height corrector consists of a slide valve which opens or closes hydraulic inlet/ outlet ports to allow fluid to flow to the suspension circuit or to be released back to the reservoir.
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| Operation of the slide valve in the hight crrector |
A control rod is connected between the anti-roll bar and the ball joint on the end of the slide valve in the height corrector. It's set up so that, at normal ride height, the slide valve is in it's central position. If a load is added to the car (passengers gearing in for example), the car sinks and the anti-roll bar twists, casing the rod to the height corrector to move the slide valve. This opens the inlet port to the suspension circuit causing the car to rise. This causes the anti-roll bar to move again...... which in turn acts on the slide valve in the height corrector causing it to move back until it reaches it's central position and once again blocks fluid to the circuit.
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| The anti-roll bar is connected to the front height corrector |
That's it's main function but, to accomplish this in a satisfactory way, it also consists of two disc valves which control the flow of a body of fluid between the two halves of the height corrector and which serve to dampen the action.
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| Disc valves (in red) on the slide valve |
The ends of the slide valve are connected to rubber diaphragms and the movement of the valve causes - and is dependent upon - the movement of fluid from one half of the connector to the other. The flow of this fluid governs the rate at which the slide valve is able to move - (and so the rate at which the car corrects its height). There is an 'easy route' and a 'hard route' between the two halves of the height corrector. The 'hard route' is via a dash pot which restricts the flow of fluid and so slows the movement of the the slide valve. Access to either of these routes depends on which disc valve is open or closed. And THAT is determined by which direction the valve is moving in......
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| Anatomy of a height corrector..... |
The disc valves are on the slide valve and, when it's in it's central position, they are normally held closed by weak springs. Shoulders on the slide valve open one or other disc valve as the slide valve moves. The slide valve being caused to move away from the central 'normal' position leaves the 'clear' route closed. Fluid is forced to move through the restricted 'dash pot' route and the initial change is gradual/ resisted. Example: when passengers get in the car, the car initially and visibly sinks fairly slowly - resisting the change.
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Moving away from centre: the disc valves leaves the 'clear passage' closed (circled in yellow).
Note the movement of the diaphragms too. |
The slide valve being caused to move back to the central position begins with the 'clear' route held open. Fluid is able to move more freely from one side of the body to the other, and so stabilisation, is more rapid. Example, once the passengers are in the car it quickly rises back to it's original height.
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Moving back to centre: fluid can initially access the 'clear path'
The slide valve initially holds one disc open.
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Removal
As with the priority valve, the front height corrector is tucked away behind the shield in the left hand wheel arch. It's bolted to the suspension unit, over the top of the anti-roll bar.
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| Front height corrector and connections on the suspension unit |
Instructions for removing the front height corrector aren't included in manual 814 (though may have been added to some PDF copies you can find on line). Those instructions are lifted from Operation DX. 433-1 in earlier manual 518.
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| Extract from Manual 518 |
I removed my front height corrector as part of work to remove the suspension unit it's bolted to - and as part of that work I removed all the pipework in the wheel arch. If you just want to remove the height corrector, you only need to disconnect the three hydraulic pipes connected to it plus the return line. Other than that, it's just held to the suspension unit by two bolts.
Repair kits can be bought from the usual suppliers. The usually include the two outer rubber dust covers plus the two inner rubber diaphragms and the steel belts that hold them in place. Citrotech sell an expanded kit that includes the inner metal discs and springs. If you don't fancy rebuilding yours, you can also get them on a part-exchange basis. Again, Citrotech offer a 'deluxe' version that has been re-bored and includes an oversized slide valve - bring performance back to 'as new'.
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| Citrotech's 'large' rebuild kit has more parts |
Dismantling and reassembly instructions are also in manual 518 - at Operation DX. 433-3. Just bear in mind that manual 518 is from 1966 and before the introduction of LMH. So, if your car and so height corrector operate on LHM, where it advises to wash parts in alcohol - don't. For LHM vehicles, use petrol or white spirits instead.
Dismantling
To aid reassembly, before you begin, it's worth taking a reference photo of the balljoint..... You should find it is at about 15 degrees to the horizontal. That's "should". The repair manual isn't at all helpful on this point.
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| 15 degree angle - according to the workshop manual |
The guide lines it shows don't line up with the angle of the actual. And what is the 'horizontal' reference point? I added the yellow lines, but they still don't help. I took the vertical to be based on the surfaces where the hydraulic connections fit - rather than the angle of the mounting bracket. And so 'horizontal, 90 degrees from that.....I think my ball joint was at about 25 degrees?
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| Not 15 degrees...... |
I have a couple of spare height correctors and they all seem to be at about this angle. It is easy to alter it later if it proves not to be correct. At the very least, having a photo will also remind you which end of the body the ball join goes on!
The rubber dust covers peel off the ends. The cover on the ball joint end can carefully be manoeuvred around the balljoint at this stage - or you can remove the balljoint and the washer beneath it by first loosening the lock nut on top of it. The ball joint part is also threaded.
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| Lock nut on the control ball joint |
Removing the rubber dust cover from the other end similarly reveals.....
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| Inner rubber diaphragm |
......another rubber diaphragm.
Removal of the nozzle for the return hose is easy. Note the use of a copper washer as that will need to be replaced.
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| Removing the return pipe nozzle |
The two metal collars around the two inner diaphragms can be carefully prised off and, with the nuts and flat metal discs removed, the inner rubber diaphragms can be removed. If you hope to re-use the diaphragms, be careful not to damage them when you take the collars off. Beneath each diaphragm is another metal disk - dished in this case - and a spring. You are also likely to find a lot of muck.
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| Metal disc, spring and lots of muck |
That muck is also all over the height corrector and in my case I couldn't initially make out any detail. |
| Muck in the height corrector |
By now both ends of the corrector will look pretty similar - especially if it's covered in dirt like mine was. Cleaning some of that dirt off reveals that at both ends there is a circlip loosely holding a disc valve. Removing one or other circlip and disc valve enables the slide valve (for that is what it is) to be pulled out.
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| Removing the slide valve |
Outside of the disc valve perimeter you will notice holes. Small at one end and slightly larger at the other. These are part of the dash pot. (The 'easy route' - the clear path - is within the area covered by the disc valve).
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| Note the small hole in the body |
Cleaning the larger dash pot hole up will reveal the head of a threaded insert. To remove this you need to make a 'key' by cutting a shallow, but wide groove in the end of something like an M7 bolt. It needs to be narrow enough to go into the hole, but wide enough to accommodate having a wide groove cut in it.If you use a bolt, it's also worth filing the threads down a little, so they do not catch in the hole.
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| 'Key' to loosen the restrictor cap on the height corrector |
Beneath this threaded insert are the restrictors: a series of VERY small discs and spacers that, together, serve to slow the flow of LHM.....As well as being very small these are VERY delicate and VERY easy to lose. Before you get stuck in, here is an idea of what is down that hole.....
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| Restrictors and spacers in the dash pot |
Either side of a central spacer is a stack of three intermediate spacers, sandwiched between four restrictor discs. So that's one central spacer, six intermediate spacers and eight restrictor discs. The restrictor discs looks similar to sequins but are much thinner and with a much smaller hole through them.
With the screw cap removed, the way to get everything out is to carefully push the stack out from the 'smaller hole' end. It's advisable to use a blunt, flat ended tool to do this - so that you don't skewer the very delicate restrictor discs. Ideally it should be as wide in diameter as the small hole allows - so that it is pushing on a bigger surface.
Now it doesn't take much to push the stack out at all. But the problem is that, on the way out, the edges of the delicate restrictor discs can catch on the threads where the cap fits - so don't push too hard or too violently. When the stack does come out be very careful. The mucky parts are stuck together and hard to see, but will stick yo your fingers in a jiffy and are easily dropped or lost without realising.
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| Eight restrictors, six intermediate spacers and a central spacer |
And that is everything disassembled.
I gave everything a rinse in white spirits and the larger parts a delicate scrub with a toothbrush. I paid particular attention to getting out any slithers of rubber pipe seals from the threads of the connections. I have an ultrasonic cleaner and put the larger parts through that. It went down like this.
VIDEO: Use of an ultrasonic cleaner
The buzzing is the high speed vibration of the cleaner. The dirt and muck just jumped off in wispy trails....... I suspended the delicate slide valve on a piece of wire - rather than have it rattle around in the cage and get damaged.I rinsed off and dried the larger parts with compressed air and then gave the parts a brush over with LHM - as protection prior to assembly.
The smaller parts were too delicate to risk losing in the cleaner. Those just got another soak in white spirit and a wipe down with a rag. You may be tempted to poke the holes through with a pin. Don't. the holes are smaller than that and their size is an important factor in making the height corrector function as it should. Instead, hold them up to the light to see if the holes are clear.
Reassembly
When it came to reassembly, the parts were so small and easy to lose that I decided to assemble them on a piece of black cloth - just so that I could keep an eye on them. I started by reinstalling the restrictors and spacers in the dash pot. This was easier than taking the parts out. Remembering the correct order of parts........
............I gave each piece a wipe over with LHM before carefully dropping it into the hole. I used the end of a cocktail stick to encourage each one to lay flat but, once they'd dropped below the level of the threads they had some 'wiggle room' and were easily manoeuvred.
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| Restacking the dash pot - halfway there..... |
The last restrictor went in and was happy to lay flat. You can just about see it - and the tiny hole in it's middle - in this photo below. And then the cap was replaced using the special tool I'd had to make. I just nipped it up.
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| Last restrictor in the dashpot |
Turning my attention to the slide valve assembly, I clipped one of the disc valves to one of the ends using a circlip. The disc is intentionally loose as it serves as plug depending on the position of the slide valve.
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Adding a disc and retaining circlip.
Note that the disc has some freedom of travel |
Before reinserting this in the height corrector body it's important to realise that the two ends are different. One end has a longer thread to accommodate the balljoint and lock nut.
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| Note that the threaded ends are slightly different lengths |
With one disc valve now fitted, I lubricated the slide valve - and the bore it would go in - and inserted it so that the longer threaded end would be on the correct side for the balljoint. Over this was placed first a spring (with it's smaller end towards the circlip)......
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One of the weak springs that hold a disc valve closed
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........and then a metal cup. |
| Spring and cup fitted. |
Note which way up the metal cup fits. It nestles in the spring. If you get the spring the wrong way up the cup doesn't fit - so you'll soon know. After this I carefully put back one of the rubber diaphragms. These had been cleaned, dried and I'd rubbed them over with a little LHM. |
| The green mark means the rubber part is 'LHM friendly' |
With a flat metal outer disc added over the diaphragm, a nut (or washer, ball joint and nut) can be added and tightened. If you find yourself working on the ball joint end first, don't worry about it's orientation at this point, the slide valve can still be rotated in the housing.
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| Ball joint refitted |
Now. At this point the workshop manual says that BOTH ends should have the diaphragms fitted and the height corrector should now be primed/ filled. This is covered in manual 518. |
| Rig for filling a height corrector........ |
The idea is to peel back slightly, the diaphragms, and then gently force LHM into the body through the overflow/ return orifice until it leaks out of the gap behind the diaphragm. Only at that point should the steel bands be added. and the overflow orifice sealed.
I chose not to do this at this time - as I don't have a rig and pump set up to fill the height corrector. It's possible I might chose to make one, or perhaps find another way to fill the corrector before I fit it.
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| Steel band refitted |
Anyway. My first steel band went on.....I'm told the steel bands can be quite tight, but I was re-using the original rubber diaphragms and steel bands and, with a smear of LHM to help them, they came together nicely.
The other end got the same treatment. If you've previously fitted the ball joint end, carefully rotate the inner assembly to give yourself the '15 degree angle' you had before dismantling. Now fit and tighten the nut to the other end. Alternatively, if you first fitted the 'nut end', fit the ball joint and use it's lock nut to give you the magical (mythical?) 15 degree angle.....
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| Both ends done now |
The last jobs were to refit the outer rubber dust covers and to refit the nozzle for the return pipe - using a new copper washer.
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| Refitting the nozzle - with a new copper washer |
Now that I type this up, I'm tempted to see what I can do to prime the height corrector before I fit it. Fluid is fed in through the return nozzle. Maybe a big syringe will allow me to create enough pressure to get the fluid into both chambers? Guess I'll have to wait and see....
