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News, views and stories from the past
An excerpt from the current Spring 2005 issue of Trident magazine |
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Vino Verde
by Andy Heywood
An intrinsic part of the character of the early seventies Maseratis comes from their use of the Citroen high-pressure hydraulic system to power everything from brakes to seat movement. This system, using as its base an engine driven pump, was first used by Citroen in the revolutionary DS but went on to feature on every medium and large Citroen until the nineties Xantia. It certainly added to the stubbornly Gallic charm of those cars, but was it really a good idea in a Maserati GT?
Citroen's ownership of Maserati between 1968 and 1975 was always supposed to be symbiotic and one of the greatest supporters of this marriage was Maserati Chief Engineer Giulio Alfieri. While it has to be said that a part of Alfieri's motivation to cement the union with Citroen was to avoid the overtures of a certain Alessandro De Tomaso, who as early as 1968, was looking to have his way with Maserati, it was also true that Alfieri had a deep appreciation of engineering solutions and the Citroen system did seem to tick a lot of boxes in those pre-electronic days.
The two main functions Citroen originally developed the system for were power assistance for braking and as a suspension medium. The famously pneumatic Citroen suspension was of no interest to Maserati (apart from in the SM) but to power assist brakes to the point where even the most effete of owners could easily apply maximum retardation was surely an advantage, while at the same time removing the need for bulky and unpredictable vacuum servos. Political posturing may ultimately have played a part in the decision-making, but there is no doubt that Alfieri embraced the French technology for
the new mid-engined GT - the Bora.
Buried at the front of every Bora engine was a hydraulic pump, belt driven from the big V8. Hydraulic fluid, known as LHM, was fed into this pump from a reservoir on the side of the engine bay and then, once pressurised, the fluid travelled to a regulator and an accumulator. When the correct operating pressure was reached, the regulator would `click' and vent the
excess. The function of the accumulator was to maintain pressure in the event of pump failure. In other words, if the engine stopped, there would still be pressure in the system for long enough to perform the essentials. This was achieved because the accumulator was basically a sphere, inside which was a diaphragm. On one side Nitrogen, on the other LHM fluid and the Nitrogen maintained a pressure on the LHM. The Citroen suspension system worked on a similar principal, but for brakes, there was another failsafe. A further two accumulators, specifically for the two separate front and rear brake circuits were also fitted, so that in the event of engine failure at maximum speed, there was enough residual pressure in the system to perform an emergency stop. |
Once pressure had been accumulated, the fluid then made its way to the brake master cylinder, no more than a pair of valves, which were either open or closed. When the driver pressed the brake pedal, it opened the valves and fed fluid under pressure to the brake callipers. In the case of the Bora, the callipers were standard Girling fare, which had been a Maserati staple
since the early sixties, although now with seals specifically compatible with LHM. For even the fluid had to be different for Citroen. Liquide Hydraulique Minerale was as the name suggests a mineral oil and developed specifically for Citroen. In the early DS days, the fluid was red but by the time the systems were used in a Maserati, it was pure green in colour. Different fluids require different compositions of rubber and therefore not just any rubber could be used for LHM pipes and seals, even those used for normal brake fluid were not good enough. So, Girling developed seals for their standard brake callipers that were LHM proof.
The advantage to the driver of LHM brakes was that the amount of movement on the brake pedal was negligible and it was merely the amount of pressure that governed the rate of retardation, a small amount being all that was required to stop normally. The disadvantage was the same thing. The lack of movement in the pedal felt foreign at first and there was a tendency to over brake until a new degree of sensitivity had been learnt. After that it still took a further period of adjustment before the driver could heel and toe. However, once mastered, the brakes were excellent and nobody could deny their effectiveness.
The Bora also used Citroen hydraulics to operate the headlamp pods, the seat movement and the pedal box adjustment, all of which was achieved with micro hydraulic rams, supplied by Bosch of all people. The headlamp circuit fed a pair of rams under the pods by means of a dashboard switch and also put the lights on by means of an electro-hydraulic switch (similar to a normal brake light switch). The seat and pedal rams also worked off rocker switches on the dashboard. The pipework that circulated all this fluid was mostly metal brake pipe, but in awkward places, or where flexibility was needed, a fine bore plastic hose was used. By today's standards, all of these solutions seem incredibly clumsy and mechanical, but in 1971, this avant garde technology helped to cement the mystical reputation of the new Maserati.
Logically, when the Merak was introduced two years later, it too made use of the LHM system for brakes and headlamp pods. Merak seats reverted to a normal type of adjustment, partly due to cost and partly because the seats had to move to allow entry for rear seat passengers. New for the Merak was LHM actuation of the clutch. As the Merak used the same gearbox as the Citroen SM, it is not surprising that it also used the same clutch hydraulics - a simple single circuit master and slave fed from the main high pressure LHM circuit. However, when the Merak SS was launched in 1976, an updated and crucially power assisted clutch hydraulic cylinder was introduced. Heavy clutches were the scourge of Seventies supercars and the Maserati/Citroen answer to criticism of such weightiness in the Bora and early Merak was very sophisticated. Operating the clutch pedal opened and closed a `low' pressure circuit within the clutch slave cylinder, causing a shuttle valve to move up and down in its bore. As it did so, it opened a port, which allowed LHM under high pressure (fed directly from the pump/
regulator) into the cylinder, which in turn operated the clutch. The theory is a kind of servo assistance as used in many a power steering system and it worked exceedingly well - pedal pressure was minimal.
With the success of the mid-engined cars and after a brief mission to equip the last 50 Indys (the 4.9s) with Citroen brakes, it was a fait accompli that for the new front engined GT, an LHM system would be used but this time, Alfieri and his co-designers at Citroen would go one step further. The Khamsin would use LHM not only for the brakes, the headlamp pods, the seat movement and the power-assisted clutch, but also for the steering. Up to that point, front-engined Maseratis had all used steering boxes but the future lay with the simpler and more direct steering rack. Part of the problem of fitting a steering rack was where to put it because the big V8 took up a lot of room in the engine bay. The packaging problem of trying to get the engine low enough in the chassis for good balance and yet still fitting a rack vexed Alfieri but his solution pleased both engineers and accountants. He used the rack from the Citroen SM. Usually, a steering rack is mounted low in the engine bay, underneath the engine and has track rods at either end linked to the front wheels. The SM unit was unusual in that the track rods came out in the middle of the rack and also because it used LHM to feed it under high pressure, it had massive self-centring which did not rely on suspension geometry. Ultimately, this meant that the rack could be mounted above the engine with idler pivots transmitting the steering input to the wheels. In some respects the linkage was tortuous, but it
achieved the desired effect of the first use of rack and pinion steering on a front-engined Maserati without the need to compromise the location of the engine.
The strong power assistance of the LHM rack was fine at parking speeds where the effort required to turn the wheel could be done withone finger. However, the Khamsin was a genuine 160mph car and ultra light steering at those speeds was no joke. In order to increase the steering feel at high speeds, a steering hardener was fitted to the rear of the car. Belt driven from one of the driveshafts and connected to the hydraulic system, it made the steering progressively heavier as speed rose.
There is no doubt that the Khamsin was the most complicated of Maserati road cars in terms of hydraulic systems, but it also had a lightness of touch that was so far ahead of it's time. One could park a Khamsin on a sixpence using the light steering, easy clutch and of course, the perspex rear window panel. In fact, the heaviest control on the car was the throttle, which had eight Weber butterflies to open.
Although the Khamsin, Merak and Bora were committed to using Citroen hydraulics for the remainder of their lifespan, once the French company relinquished its control and De Tomaso finally got what he wanted, Maserati reverted to more conventional hydraulics, and indeed more conventional cars. It is not unreasonable to expect that having bought the company, one would wish to rid it of the previous management's USP, but also the relationship between De Tomaso and Alfieri was such that the great engineer, who had been loyal since the 250F, was sacked without explanation and forced to work out his pension at Lamborghini. Interesting as they were in their own right, one cannot help but feel that the Kyalami and Quattroporte III lacked the engineering excitement of their predecessorsWhile the last Khamsins and Merak SS cars were made in 1982, the LHM system had technically died some years before. Citroen, themselves victim of a hostile takeover by Peugeot in 1975, were never again able to dictate terms to anyone. Over the next two decades, ever-hungry accountants would systematically remove their eccentricity and ingenuity. Only today, with the advent of cars like the new C4, have they been able to return to some kind of form, albeit in a retro way. For Maserati, the Citroen era was only a small part of what we all know is an incredibly diverse back catalogue. Yet it left its mark at a particularly impressionable time in the history of the Italian Supercar.
LHM Today.
For the most part, LHM systems are very reliable, but like a lot of Maserati technical problems, they suffer at the hands of those without the knowledge and experience to properly diagnose or deal with them. In order to help owners and potential owners, following are the most common problems and their solutions:
1. Water ingress. Particularly on Meraks and Khamsins, the proximity of the LHM reservoir to a bonnet vent allows rainwater
to gather on the top of the reservoir and if the rubber filler neck is not properly sealed, the water will get into the tank. You can tell if there is water in the tank by looking at asample of the fluid. If it is clear dark green, it is OK but if it is translucent or cloudy and light green, it has mixed with water. While the system will continue to work, the water will steadily corrode moving parts, causing leaks. To remove the water, drain and bleed the system.
2. What is LHM flush? A mixture of LHM fluid, engine oil and paraffin can be used to `flush' the system to remove debris, water etc. Depending on how contaminated the system is, the flush can be kept in for up to one month before being drained and refilled with fresh LHM. Worth doing if you suspect water in the system.
3. How do I tell if my system is up to pressure? On a cold start, the LHM system will take a while to reach operating pressure. All of the Maseratis are fitted with a large red light on the dashboard warning of low pressure. On Khamsins and American specification cars, there is also a buzzer, which sounds until working pressure has been reached. If you are not sure whether your light works, get it tested because this could be very useful if you had a hydraulic failure. However, even a system in poor condition can usually reach working pressure, the crucial thing is how long it could maintain it if the pump (in other words engine) stopped. To give you some idea, run the engine until the red light goes out. Stop the engine and then operate the headlamp pods up and down as many times as you can until they will not move (in other words, until pressure has dropped). On a healthy system, they should go up twelve times. The minimum is six and anything under that requires theaccumulators recharging. Remember that in the event of an engine failure, the accumulated pressure is all that will stop you!
4. When the red light comes on, do I have to stop? Frankly, yes. Even if your system is in perfect condition, you will still only have enough accumulated pressure to perform a full stop before you lose the brakes. As an aside, I was once driving a Merak on a motorway at speed when an oil cooler hose split. In order to avoid starving the engine of oil, I turned it off and then had to rely on accumulator pressure to stop me. As I rolled to the top of a convenient slip road, it was the gradient that actually stopped me.
5. How do I tell if I need more LHM fluid? The original equipment reservoirs have a sight glass through which the fluid level can be judged. Technically, the engine should be running while this check is taking place. However, if any fluid is required between services, there is likely to be a leak that requires investigation.
6. My MOT tester has just failed my car because the headlamps are leaking. How can this be? It is the headlamp pod ram that is leaking and he is technically correct as this is classed as a brake fluid leak.
7. I heard that you have to use the headlamps to bleed the clutch on a Merak. Is this true? Yes. On the Merak SS and also the Khamsin fitted with the power assisted clutch slave cylinder, pockets of air can make their way into the return pipework for the headlamp circuit during the bleeding process. In order to push these air pockets through the slave cylinder and out of the system, operate the headlamp pods at the same time asdepressing the clutch pedal.
8. There is a strange clunking noise every few seconds coming from above my right knee when driving my Khamsin. What is it? The LHM regulator is fitted on the other side of the bulkhead and makes a clunk every time it cuts out as operating pressure has been reached. This should only happen every 30 seconds or so unless parking (i.e. using steering, clutch and brakes at the same time) but if on the open road the clunk is more regular, the chances are that there is a problem with the clutch slave cylinder - its high pressure circuit could be worn and allowing fluid to escape all the time which in turn would cause the regulator to work harder to maintain pressure.
9. Last year, my local garage replaced the rubber hose that feeds fluid from the reservoir to the LHM pump on my Merak. I looked at the hose again the other day and it seems to have become bloated and sticky to the touch. Is this OK? No. Your local garage has not appreciated the fact that LHM attacks conventional rubber and that any rubber part in contact with the fluid needs to be specifically matched to it.
10. The plastic heel pad on the driver's footwell in my Bora always seems to be slippery, no matter how often I clean it. Why? You probably have an LHM leak from either the headlamp switch or the seat/pedal move ment switches, which is dripping, onto your carpet.
11. Someone once told me that when I park the car in the garage for a while, I should pump the brake pedal. Is this true and why? It is true that an LHM system in good condition will maintain pressure for some time afterthe engine is switched off and therefore, if you are intending to leave the car, you could minimise stress on the various seals in the system by pumping the brakes until the pressure has dropped.
12.1 know that the steering on my Khamsin is supposed to be light at parking speeds, but it is still very light at higher speeds and really difficult to drive. Is this right? It sounds like the steering hardener is not doing its job. Most of the time, this is because the belt has fallen off, but sometimes it can be a hydraulic fault.
Hopefully a few horror stories averted. If you have any tales of the LHM system or any queries, let us know and we will attempt to answer them either in a future issue or in the Newsletter.
This article first appeared in the Spring 2005 issue of Trident
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Maserati enthusiasts and collectors who may be interested in acquiring back issues of this highly collectable magazine may do so by contacting Adam Painter of the Maserati Club at
adamkpainter@uk2.net
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