TECHNOLOGY   PASSION   INNOVATION

Gear change

The standard CAV gear change is quite frankly awful I have no good words to say about it. The owner of this car commented that his mates used to laugh at him when they went to trackdays because they could hear him trying to find a gear!


The original GT40 has the gear change on the right hand side sill. This allows a direct path for a rod to connect to the gearbox in a rear engined car.

Putting the gear change in the centre of a rear engined car makes connecting to the gearbox very difficult as there is no direct route to the gearbox because the engine is in the way.


Locating the gear change on the right-hand sill of a CAV GT40 is possible to do but without compromising the sill strength gets a bit involved. So we had to improve the central change.


The ZF gearbox in this car has a dog leg 1st gear with reverse forward and to the left. So without a lock out of some description it is conceivable that you could go into reverse instead of second - not good!

The solution we decided to use was a hybrid rod and cable system - lever end of the mechanism would be used to operate cables that where directly connected to the gearbox actuating arm.


We used an original style billet aluminium gearlever mechanism placed on a special mounting that allowed the electronic handbrake mechanism to work underneath it.  The lever mechanism copies the original item which has the added bonus of already having the reverse lock out taken care of, it also looks right in a GT40.

The routing of the cables was carefully worked out to minimise bends which decrease the efficiency of the cable which adds free play at the lever.


As special housing was designed to mount the cross gate cable on the gearbox. As well as allowing a cable mounting point we tweaked the internals of this housing to help reduce the force required to move the gear lever in the cross gate plane.


The result of all this work is a gear change that is very positive and has a very solid feel. I know this sounds odd but you don't think about using it - it just works.

Taylor Automotive Engineering

Unit 3 Willow Farm

Scrapers Hill

Chiddingly

East Sussex

BN8 6HJ


Telephone: 01825 873578

Email: geoff@taylor-automotive.co.uk

CAV GT04 DTC  

CAV GT04 DTC has been a regular in the workshop over the past few years. It is now a highly developed CAV far in advance of what left the factory. Here are some details about a few of the items that have been re-engineered on this car.

Dry sump oil System

When this car first came into the workshop the fuel and oil system on the engine were shocking. There was a film of oil over everything in the engine bay due to inadequate engine oil breathers. The dry sump tank was one of the smallest I've ever seen and the mix of pipes and fittings was horrific.


The oil system was redesigned to use a modified Peterson dry sump tank that extends into the sill.


We remade all the pipe work to including a ducted, thermostatically controlled oil cooler underneath the gearbox and remote oil filter. We also made proper machined billet aluminium brackets to hold the oil pump, alternator and crankshaft sensor.

Fuel System

A fuel injected GT40 with two individual fuel tanks is about the most complicated fuel system you can imagine if installed correctly. Squeezing it into a monocoque chassis also presents many challenges even more when room has to be made for a dry sump tank as well!


The fuel system uses two Carter high volume, low pressure lift pumps to supply a reservoir. This tank provides an uninterrupted supply of fuel for the high pressure injection pump. Pressure is regulated by a fuel Lab bypass regulator. This returns unwanted fuel back to the reservoir tank. Any excess fuel at the reservoir tank needs to be returned back to the main tank from which it came. This is achieved by two solenoid valves that direct the return fuel to the appropriate tank. Various filters and one way valves are also used in the system to ensure the system functions correctly.

The reservoir tank, both solenoid valves, high pressure regulator, high pressure pump and filter are all housed in one removable module that fits in the rear of the drivers sill.

These components were originally perched on top of the rear driver side sill being cooked by the exhaust. The assembly was held together with cable ties and constructed with a mix of steel, aluminium and push on fittings - all very amateur.

We also reworked the throttle mechanism in the centre of the inlet manifold to improve the throttle weight and progression.

Front suspension & steering

When I first drove the car the steering was slightly nervous and there was some bump-steer present. The steering was very light and I didn't have the confidence to take my hands off the steering wheel at higher speeds. The car also had a tendency to bobble over humps in the road - something that made the car feel unrefined.


We converted the front suspension to be fully adjustable using newly fabricated wishbones and rose joints. This allowed us to add more castor which has improved the feel and stability of the steering. In adding more castor we effectively moved the steering arm attachment point on the upright which if not corrected would have added more bump steer. To correct this we designed some billet steel bolt on steering arms that position the steering ball joint at the right height on the upright thus eliminating bump-steer completely.


The ride quality was improved dramatically by fitting double adjustable Koni dampers. The original dampers only had adjustment in bump - this just wasn't enough to control the suspension on the UK's roads. With dampers you really do get what you pay for, the Koni's are relatively expensive but these units will stay on the car for its life. They are fully rebuildable and all the internal valving can be adjusted if necessary - a very wise investment in my opinion.

Braking System

As standard CAV fit six piston front and four piston rear calipers with 300x32mm discs and a direct acting servo. The Wilwood calipers are a capable caliper but on this car the brakes didn't really inspire confidence because the brake pedal travel was so long. There are two factors at work here - first the master cylinder bore size and secondly the amount of assistance the servo gives. The CAV uses an OEM direct acting servo/master cylinder unit so tuning the master cylinder sizes to improve braking isn't really an option. The servo is dependent on vacuum from the engine to generate extra force on the piston in the master cylinder. If we increase the amount of vacuum the servo see's we can increase the brake pressures. This was achieved by using a forerunner of the eVac system. The system uses an electric pump to generate vacuum rather than the engine. Now we have plenty of assistance from the servo we can adjust pedal feel by adding in an intermediate link between the brake pedal and the push rod of the master cylinder piston. This has the effect of making the pedal firmer but due to the increased assistance from the servo the brake pressures are increased. The result - proper brakes as you would expect on a car of this type.


The handbrake on this car is also unique amongst GT40's - it is electronic. It uses a mid mounted electric servo to actuate specially adapted Wilwood handbrake calipers. The need for this type of arrangement was twofold. Firstly to accommodate the hybrid rod gear change mechanism in the central tunnel it meant there was no room for a conventional handbrake lever system. Secondly the amount of force required to slow down a 335mm wide tyre is more than could be generated with a simple hand operated lever system. The actuator in this system delivers 600lbs of clamping force to the calipers.

Gearbox cross gate cable mounting & housing

Gearbox cross gate cable mounting & housing

New tank position

New oil pump bracket & crank sensor mounting

The tip of the iceberg

Original arrangement

What lies beneath what you can see

New steering arms

New wishbone set

Pedal assembly intermediate link

Modified Wilwood handbrake caliper