Retro Fit Overdrive System
With 45 years experience of maintaining Rolls-Royce and Bentley Motor Cars we first introduced an overdrive system for pre-war cars in the late 1980’s.
Now, for all those considering a ‘fifth gear’ we have further refined the overdrive system which received such high acclaim from Lt. Col. Eric Barras, President of the Rolls-Royce Enthusiast Club, when it was first introduced. It utilises the tried and tested Laycock Unit, suspended or mounted and self aligning using flexible mounts on a specially designed cross-member system. The complete package including balanced prop-shafts, wiring loom, speedometer drive etc, and has been recently revised to appeal to the self-fit customer.
Easily fitted and replacing the existing prop-shaft, there is no need for drilling, welding or the re-routing of ‘one-shot’ pipes or the existing wiring harness. In addition the complete installation can be removed at any time, leaving absolutely no trace. Each Laycock Unit is produced to order with a matched speedometer drive ratio. The Overdrive is operated by the flick of a switch, whilst engagement is restricted, for design reasons, to top gear.
These overdrive systems are suitable for all ladder frame & cruciform chassis vehicles originally fitted with a prop-shaft.
Please note on some cars with drop foot wells modifications may be required or unit will be installed into rear crossmember.
A full ‘Factory Fitting Service’ is also available, and collection and delivery of your car can be arranged if required.
Typical overdrive kit will include:
- Laycock Overdrive unit complete with speedo drive to suit
- Cross members and rubber mounting system
- Mounting clamps and adhesive
- Intermediate shaft with custom machined ends
- Rear prop shaft with custom machined ends
- Blanking cover for original speedo drive
- Speedometer extension cable
- Extension cable adapter
- Wiring harness, complete with switches, relay and fuses
- 'Overdrive' escutcheon for master switch
- Wiring clips
- Nut and bolt fitting kit
- Installation instructions
Typical overdrive package contents:
Technical information:
The engagement of the Overdrive gear is hydro-electrical. An integral plunger pump, driven by the input shaft, provides the regulated hydraulic pressure, which is controlled by an electric solenoid valve, switch operated from the dashboard.
Because the efficiency of the plunger pump is directly proportional to the RPM of the gearbox output shaft, it is important that engagement of the overdrive is limited to top gear and an inhibitor switch is provided for this purpose.
The Overdrive is suspended from or mounted onto a substantial cross member, which is bonded and clamped to the chassis. Rubber mounts and silent blocks are used, in a configuration designed to limit oscillation/vibration, insulate the Overdrive and eliminate the transmission of noise.
On the road:
For a given road speed, the Overdrive will reduce the engine revs by 22%:
| Direct drive | 50mph | 2,500rpm |
| Overdrive engaged | 50mph | 1,960rpm |
Conversely, and of interest to Motorway users and those considering touring, for a given engine speed the Overdrive will provide an additional 28% of road speed:
| Direct drive | 2500rpm | 50mph |
| Overdrive engaged | 2500rpm | 64mph |
Current package prices:
| All Small H/P Cars to 4.25 ltrs: | £2500.00 +VAT |
| Cars Above 4.25ltrs: Phantoms & Wraiths: | £2650.00 +VAT |
| Fitting at Taunton Factory | £1200.00 +VAT |
All kits come with a 12 month warranty
To order
Kindly measure your vehicle and enter the information by printing out the following downloadable forms:
Please note that accurate recording of all dimensions is essential to ensure satisfactory installation and performance as each Overdrive Package is tailored to the customers declared specification.
For more information please contact us.