Adding a Brake Servo

Dave Pilbeam

Despite having fitted 306mm vented front discs and Dynalite 2 brake callipers and a new Jag IRS rear end with brake discs Eleanor showed a marked reluctance to stop in quite exactly the same way that modern cars do. You know, the sort of brake system that allows your 95 year old granny to stop a 2 ton Mercedes by merely breathing on the brake pedal. In the mid 60s anyone driving a car like a Cobra would be assumed to have a Schwarzeneger right leg. Now that doesn’t apply to me, no siree and it definitely does not apply to Amanda, or so she says!

I had considered fitting a servo in the past but decided not to because I believed that having a servo would remove any kind of “feel” to them. In addition I had DOT 5 or silicone brake fluid slopping about the system and I was loath to change that to something more corrosive and hydroscopic.

However, having decided that Amanda should be encouraged to drive Eleanor (for those rare trips down to the pub on a Saturday afternoon) and having adjusted the drivers seat so that short(er) legs could reach the pedals I felt honour bound to make the necessary improvements to the braking system.

I had already bought the twin circuit remote servo from Stafford Vehicle Components www.s-v-c.co.uk tel: 0845 581251. Actually I had ordered it in August 2003 and it eventually arrived in August 2004. The servo cost £245 including delivery following a re-tooling of the factory which caused the 12 month delay in receipt.

Having re-read Adrian Bowden’s excellent article in the Winter 2002 newsletter I resolved to fix the problems he encountered and determine if I could improve upon his experience. I’m not sure I have done either but the braking is certainly greatly improved.

The first problem, or challenge, that Adrian encountered was where to locate the servo. Adrian fitted his between the radiator and the engine. I decided that fitting it there was too difficult and might have implications for cooling and bleeding. I have no evidence for this decision but an alternate location was possible on the front bulkhead, which would at least aid brake bleeding.

The downside was that I had to remove and replace the heater, and that caused some difficulty, not least of which that I managed to trap a windscreen washer hose in the process!

In order to mount the servo on the bulkhead I constructed a suitable bracket out of 4mm mild steel plate being careful to allow removal of the servo at a later date without having to remove the heater, yet again.

The second problem that Adrian faced was how to connect the servo into the existing braking system. Rather than use rigid pipes I elected to use stainless steel flexible tubing. This is more expensive but as a by-product of that decision I could use banjo connections to the servo which, fortunately, avoided the problem Adrian discovered in using 3/8” UNF male fittings.

I estimate that I spent around £100 in stainless steel braided tubing and fittings. For those I can thoroughly recommend Think Automotive in Isleworth, www.thinkauto.com, tel: 0208 568 1172. Whilst Think Automotive can make up the tubing with the fittings you need I found it more convenient and actually pretty easy to make up the tubing myself. I had tried to do this in the past with not much success as cutting the SS flexy tube was very difficult using a hacksaw, even after taping up the ends.

This time I fitted a steel cutting disc to my 4½” grinder and this made cutting the tube extremely simple. With a few extra olives, in case of error, I found it to be very satisfying making up my own brake pipes. If you are tempted to do this yourself go for the Moquip TFE – 3 stainless hose. It’s only? £5.60 metre, instead of the Aeroquip variety which is around £18.80 a metre.

In order to connect the servo into the inlet manifold I too used the Rimmer servo non-return valve (part No. ADU1402), cost £17.25.

This screwed right into the rear of my JWR Offenhauser dual port manifold. There was already a tapping there which was blanked off with a plug.

All I did was remove the plug and fit the valve using some PTFE plumbers tape around the thread to keep it airtight.

I also had to purchase a 3/8”/10mm 90 elbow for £2.50 from Car Builder Solutions in Staplehurst, www.nfauto.co.uk tel: 01580 891309 to connect the valve to the servo. Be sure to use proper servo hose for this as it resists collapsing due to the vacuum.

Of course, in order to be able to use the system I wasn’t able to continue with DOT 5 silicone brake fluid. Apparently, it is too viscous to use in servos. Despite the considerable effort of flushing and bleeding with new DOT 5.1 mineral based fluid the system works well and the brakes are just STUPENDOUS.

I have no hesitation in recommending this worthwhile enhancement.

And doesn’t it look great too?

Rover Speedo Tip

John Coward

I thought I would let you all know how a speedo problem in my Hawk was finally resolved by Andy at Speedy Cables. Neither the standard instructions out of the EPS speedo box, nor the Caerbont website instructions, nor the standard Hawk Rover wiring loom will work with Rover SD1 gearbox senders, also known as transducers.

It’s easy to fix the wiring loom, the black earth wire is not needed by the Rover SD1 sender at all. Instead I ran a new green 12v positive from the reversing light switch to the sender black/ yellow. The other sender brown wire connects to the standard loom purple/blue, which in turn connects to the speedo white/black. The speedo red connects to black 12v negative earth, NOT green 12v positive, which is specified in the

EPS speedo fitting instructions and on the Caerbont website.

The other useful bit of information when programming the EPS speedo, is that the Rover transducer appears to send 64 pulses per revolution. I got it wrong by a factor of two, and then found that I was travelling down my residential road in Beckenham at 70 mph. I have also discovered the only known practical use for those highly annoying radar electronic speed displays now spreading everywhere – you can calibrate your EPS speedo with them.

Hawk 289 Le Mans – my build experience - Part 1

John Coward

The Hawk 289 Le Mans is a close replica of the two AC Cobras which competed in the 1963 Le Mans. One retired and the other, 39PH, driven by Peter Bolton and Ninian Sanderson, came 7^th after 6 Ferraris. The streamlined hardtop allowed the car to achieve over 165mph on the Mulsanne straight. The car was an evolutionary step, leading to the development of the Shelby Daytona, Willment and AC coupés in 1964.

I started building my Le Mans six years ago, and it has only now passed the SVA test!

This may be an all time record, but it’s not one I’m particularly proud about – my only excuse is that I have been frequently diverted to sort out my daughter’s Morris Minor, garden, decorate, work, etc. But the Hawk is now on the road, and is a talking point whenever it stops, even though it is still unpainted and untrimmed (see above).

In 1999, there was only a draft build manual available for the Hawk, plus of course Gerry Hawkridge’s invaluable advice. Very soon though, a succession of 289 newsletters provided a wealth of information about other owners’ builds and improvements, which I found particularly useful – even when I decided not to carry out a reported improvement! So I feel I should rather belatedly pass on some of my own experience – and rather than cover ground already well documented, I thought I’d write about some of the specific aspects of building the 289 Le Mans, and some other issues which I don’t believe have been covered in these pages so far.

Not having built a kit or component car before, my original objective was to build the Hawk in the simplest and cheapest way possible, and to use standard components so that the car is as easy to maintain as a Morris Minor or MGB. This meant that I chose the Rover V8 engine / MGB running gear combination. Although this limits the degree of originality possible under the bonnet, I have tried to keep the outside of the car as close as possible to the two cars which ran in the 1963 Le Mans. I’ve noted below all the divergences from the original race cars of which I’m aware from contemporary photos, including those which have been caused by the SVA rules. As I want to use the car all year round, unlike a 289 roadster, some compromise is needed.

I have found that a key admin task when building a kit car is to keep track of all the components installed: the supplier, the manufacturer and any modifications made At first, I did not realise the uniqueness of every kit car. My memory is poor, so it helps me, and of course a full specification will assist if I ever sell the car to a new owner.

Le Mans hardtop and side screens

This is the most attractive feature of the Le Mans car, but also involves a fair amount of work to build. As you can’t submit the car for SVA with the hardtop attached (because of the sharp catches on the windscreen stanchions) some of the work can be deferred, but you will need the hardtop in place temporarily to install the windscreen.

The first problem I had in my single car garage was finding a place to put the hardtop while working on the rest of the car. The only way I found to avoid it getting damaged was to suspend the hardtop from the garage roof, using some pulleys, nylon rope and hooks screwed in the ceiling – it’s best to arrange this so you can raise and lower single handed, by attaching the ends of the rope to an eye or hook fixed in the wall.

When installing this hardtop, the critical issue is the amount of driver headroom. You should check this is OK before you buy this model! I did not, but found that both I (at 5’ 11”) and my flat cap could just squeeze in. You always have the option to omit the seat runners and bolt the seats directly to the floor, but you won’t gain that much headroom and you will lose the flexibility to cope with different drivers.

The hardtop sits on the rear deck of the car with two rubber seals protecting the surfaces, positioned on the inner and outer edges of the hardtop flange. The outer seal has a double bead, and this slightly thicker seal raises the hardtop very slightly and helps to give more headroom. Therefore, you need to install some temporary short lengths of seal on your hardtop flanges before starting to install the windscreen.

The two side vents are cut out from the hardtop, and then a metal grill mesh fitted from the inside. Each mesh is cut oversize so that two flaps can be bent and glued to the inside of the hard top with resin. My mesh came from a Morris Minor speaker grill. They were quite common in cars of that era. See the photo below.

The fuel filler flange is positioned within the frenched recess of the hardtop, and bolted on with six 5mm bolts. With care, you can tap holes in the hard top, as it is quite thick, but I thought it more secure to drill through and fit domed nuts and washers underneath. However, with the lower filler flange installed on the top of the boot above the tank, it is best to tap the holes, as you can’t fit nuts below so easily.

The fitting of the metal corners and the side screens are covered in the manual or newsletters and are no different from the standard hardtop. You must fit the side brackets to the hardtop which locate it transversely on the body, before you fit the side screens. You also should first make sure the doors are closing in the correct position.

To make the side brackets which allow the hardtop to be bolted to the body, I used some window channel off cuts, from cutting the side screens to size. The channel is light but strong and protects the bolt head. It is positioned just inside the corner of the hardtop – I drilled and fitted a small self tapping screw to locate the bracket correctly, before applying strips of fibre glass and resin to hold the bracket in place. I then cut the end of the screw off where it protruded through the flange of the hardtop. The photo below shows the bracket before the fibre glass strips were applied.

Eventually, I plan to get the inside of the hardtop covered with grey flock.

Rear window

A few words on fitting the rear window might be helpful – I found this tricky. You have an option to either bolt in the perspex window, which is what had to be done on the original cars when they blew out at 150 mph, or install a rubber seal and locking strip, which looks neater and is more waterproof. I chose the rubber seal option!

The rubber seal has two slots, one 3mm and the other 3.5mm. The smaller slot is fitted against the hardtop edge, the larger to the perspex edge – this gives more wiggle room when finally installing the window. There is a V shaped locking strip which fits on the outside of the rubber after the window is fitted, and holds everything in place.

The first thing to realise is that both the hardtop and the perspex as supplied need shaping to the correct window aperture. The size of this aperture is determined by the edge of the window recess in the hardtop, and the thickness of the outer rubber seal,

which should be installed to fit snugly (1-2 mm gap) against the edge of the recess. I made a simple metal gauge to mark out the line of the aperture a fixed distance from the recess edge. The aperture can then be opened out carefully using a half round file.

Next, the perspex needs to be shaped to fit within this aperture, leaving a small but consistent gap to allow for the thickness of the separator in the rubber seal.

With care, you can use an angle grinder on the perspex. The rest is trial and error!

When finally fitting the window, ensure that the join of the rubber seal is centralised in the window, and the locking strip join also centralised, but opposite the main join.

Windscreen

Unlike the roadster which has a more upright windscreen, the Le Mans windscreen is inclined backwards at about 45 degrees. When installing, you need to put two pieces of 1/8” hardboard between the bottom of the windscreen and the scuttle, by each stanchion, to set the screen at the correct height. The lower edge of the windscreen is set a little higher than on the roadster, which helps the headroom under the hardtop, but the rubber weatherseal at the bottom of the windscreen must still make good contact with the scuttle to maintain some degree of weather proofing. The gap at the centre of the windscreen between the screen frame and the scuttle is about ¾”. The bracket which fixes the two together has to be inverted, and bent to suit the 45° angle.

Once the positioning had been fixed against the hardtop, I made up a wooden prop to hold the centre of the windscreen at the correct height without the hardtop in place.

The position of the wiper bosses needs to match the 45 degree angle of the windscreen, as do the washer jets. Do not assume that the original markings on the body are correct because they may be designed for the roadster. You must check that the wipers and washer jets are correctly positioned relative to the windscreen.

You will find that the windscreen heater vents need positioning much further back than on the roadster model, to direct the airflow on to the screen correctly.

Fuel Tank and Filler

Whereas the 289 roadster fuel filler is central, on the Le Mans the fuel tank is shaped asymmetrically with the filler exit close to front offside. This means that, assuming you have run the rear wiring loom and tank breather tube across the top of the rear bulkhead, you have to be careful positioning the flange bolt holes for the filler so that they don’t hit the wires and tube. These 5mm bolt holes should be tapped, so you don’t need to struggle attaching nuts in the difficult to reach space over the front of the fuel tank.

Boot with split boot lid

Another Le Mans feature, this allows the lower part of the boot to be opened without removing the hardtop. The only tricky thing I found was replacing the hinge bolts after temporary removal of the lower boot-lid. The nuts are hard to get to. The solution is to remove the threaded rod and nut from the hinge, and draw them up through the slightly enlarged bolt hole from behind the lower bodywork, using string or a rubber tube. The hinge sharp edges can cause issues with some SVA examiners. The upper boot lid can be fitted with the standard prop, which attaches conveniently to the outer hinge bolt, as it does not carry so much weight as the standard boot lid.

Inside the boot behind the rear wheel arches, I have fitted small plywood platforms covering the wiring and chassis bolts. Even so, the SVA man insisted on the wiring all being taped down underneath. I also plan to fit a plywood or aluminium alloy bulkhead behind the tank to provide protection from luggage, and also somewhere to stow the side screens and bottle jack.

Lifting hooks

Also fitted to the FIA model, the problem with these quick lift hooks is that they don’t pass SVA or MOT in standard form. Some of the rear edges need a radius of 2.5mm as well as the forward facing edges, and the front lifting hooks must be turned round so they face rearwards. I also ran a length of copper pipe between the front hooks, to carry the number plate without drilling the bodywork, but this is not needed for SVA.

I could have just removed the hooks completely for the SVA test, and reinstated them afterwards, but I think this is one of the SVA provisions which need to be adhered to on a road car, and I wanted to make sure that I both passed the test and remained safe!

Driver roll hoop, forward strut and seats

The hoop just fits underneath the hardtop. The forward strut from the hoop to the nearside chassis by the gearbox needs to be fitted before you finalise the position of the passenger seat. This is because this seat must be positioned about ½ “further to the nearside of the car, compared to the driver’s seat, in order to clear the strut.

As a result, the rear inner bolt fixing the passenger seat is difficult to install, because it will probably hit the main chassis member. My solution was to cut transverse slots on all three seat fixing holes in the floor on the passenger side. This allowed all the seat bolts and nuts to be installed loosely, with the seat moved temporarily about ½” towards the driver, then moved back to the correct position for final tightening.

The rear outer bolt seat fixing should pass through the chassis member, and in order to achieve this, I found that an extra hole in each seat runner was required 1” from the rear ends. The front inner bolt fixing on both seats cannot be installed, because of the transverse chassis member behind the gearbox. However, three bolts should be sufficient to hold the seats down securely.

Dashboard and steering wheel

On the Le Mans, the inclined windscreen forces the steering column to be set at or near the bottom of the dashboard slot. On my car, I found that I had to elongate the slots in the steering column bracket behind the dashboard to allow this to happen.

The SVA rules constrain the dashboard severely, sometimes in unexpected ways.

Originally, I fitted the rev counter in the higher left-hand position, in the driver’s line of sight, copying the typical race car layout. However, the Mini Metro steering wheel required for SVA purposes then obscured the speedometer dial and caused a failure. So in order to pass the SVA, I had to swap the speedo and rev counter around.

Another SVA issue with this steering wheel is that, on my car at any rate, the thick rim was too close to the indicator switch – I had to try to extend the steering column a fraction by adjusting the universal joints. In the end, the SVA examiner took pity on me and allowed the car to pass with a clearance of ¾” – OK if you have thin fingers. This steering wheel will of course be replaced post SVA – although I rather like it.

I fitted an extra switch to control the radiator fans. The only SVA friendly position is underneath the lower central portion of the dashboard – so I moved the heater switch there, and mounted the new fan switch on the face of the dashboard in the vacant hole.

I also fitted a starter push button, mainly because the ignition switch kept turning in the dashboard. It does look the part, although to be authentic it should work the horn. It is fitted adjacent to the ignition switch, in the SVA exempt area behind the wheel.

For the (post SVA) future, I intend installing a battery cut off on the dashboard – at present it lurks in the engine compartment on top of the passenger foot well. Panels within both foot wells run from the front to the edge of the dashboard and prevent leg contact with various sharp edges. Although only required for the SVA, these panels also conceal the immobiliser electrics and protect the accelerator pedal lever arm, so they will stay in position despite their lack of originality, as they are difficult to see.

I made the panels out of 5mm plywood with reinforcing ½” battens fixed behind.

Brakes

Although the original race cars had no servo assistance, I did not feel comfortable without a servo in a modern road car. I read the account of a Spanish manufactured servo installation in a recent 289 newsletter, but it seemed complex to plumb into both braking circuits and somewhat problematic to install.

I consulted Gerry and he suggested fitting a standard Lockheed servo kit, on the front braking circuit only. This was surprisingly easy to install, I fitted it to the bottom of the header tank bracket on the nearside of the engine compartment, and there is plenty of space. The plumbing is easy because the rear circuit is left undisturbed – I installed the servo after the original unassisted brake hydraulics and the engine had been fitted.

The installation looks right for the 1960s period, it sits low in the engine compartment just above the steering rack, and the servo reservoir does not obscure much of the air flow through the radiator. See the photo below – the inclined angle of the servo unit is necessary for ease of bleeding the system, and the hydraulic pipes were clipped to the chassis and sides of the engine compartment on the front and offside of the engine.

When bleeding the front brakes after a complete fill of hydraulic fluid, it is necessary to disconnect the pushrod for the rear circuit from the Tilton bar, otherwise you cannot get a sufficiently long stroke and fluid displacement through the cylinders. Also vice versa.