5 replaces 4

Early March: We’ve had a 4.2 litre fixed headed coupe Jaguar E-type coated with a dazzling emerald green roll into our workshop. Our client required a more modern 5-speed gearbox to replace the original 4-speed transmission which was the technology of the time. A few custom made E-types had overdrive fitted to their gearbox between between its production from 1961 to 1975 but it wasn’t as popular as their normal 4-speed manual and 3-speed automatic popularised by the American market. Although the application of the overdrive technology was becoming the favourite choice of ride between the E-types older cousin, MK II saloon series, the beefy straight six engine E-types were all about sportier experience than comfort. The big cat of the 60’s that became Britain’s fastest production car could produce 265bhp and reach up to 150mph.

You might be asking yourself why would you want to upgrade the original 4-speed transmission with a modern 5 speed unit? Well the most obvious factor which the majority of customers consider when doing such a change is that in a 5 speed gearbox the engine wouldn’t require as much rev to achieve the same output. Revving the engine less not only reduces engine vibration that can put stress on the chassis and crack growth but also consequently reduces the wear and heat inside the engine which helps make it last much longer with a better output power over time.

The task of fitting the transmission was assigned to our technician, David Johnson, with 2 decades of spannering around the classic Jaguars. The whole project took around 60 hours including extensive road testing. David or DJ as we know him in the workshop (due to his engine tuning abilities) faced various difficulties during the process. In order to replace the gearbox, first the bonnet and engine needed to be removed and to tackle such a task, the exhaust, carburettors, inlet manifold and exhaust manifolds needed to be separated. Sequentially, the suspension tension needed to be drastically reduced since the 350kg engine is taken off its total sprung weight. The clutch plate was also upgraded to a bespoke plate to match with the new transmission ensuring maximum efficiency in power output. The propshaft was delivered to the local ‘propshaft guru’ to adjust the length to suit the modern gearbox, and weight balanced perfection. The new gearbox casing had to be modified slightly for a perfect fit within the chassis which was designed for he Moss 4-speed gearbox.

The most commonly faced problem after assembly to avoid, depending on engine and gearbox positioning, is potential rubbing between the propshaft and handbrake mechanism which have to be carefully adjusted to create the perfect ride envisioned by Jaguar.

For your E-Type’s gearbox upgrade, please don’t hesitate to get in touch using the contact form below or via our usual contact details :

0115 9262266 or info@thorntonrestorations.com