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MGB 5 Speed Gearbox Conversion Kit: 1800 Models

The MGB 5 speed gearbox conversion kit has been developed as a logical successor to the popular MGA 5 speed gearbox conversion designed and developed by Hi-Gear Engineering Ltd.

MGB 5 Speed Gearbox Conversion Kit: 1800 Models

The kit is aimed at owners of non-overdrive MGB cars, owners who have reliability problems with existing overdrive units and owners who want to upgrade the vehicle performance in line with modern practice with all ratios under the control of clutch and gear lever.

Two kits are available to cover all 4 synchro MGB cars with the wider gearbox tunnel and the 3 synchro models with narrow tunnel.

The conversion adapts a Ford Sierra type 9 gearbox (5 speed, 1.6L & 1.8L, 1982-91, & 2.0L: 1982-87) to the MGB engine.

The standard ratios of the Sierra gearbox suit the MGB well with a 10% higher second gear for better overtaking. The 5th gear ratio is exactly the same as the MGB overdrive ratio.

Various alternative gear ratios can be provided including a closer ratio gearbox and a standard ratio gearbox with a higher first gear ratio of 2.98:1

The conversion is totally non-intrusive to the MGB. There are no holes to drill, no metal to cut or remove, the car can be returned to standard easily if and when required.

The kit is supplied with all parts, nuts and bolts and fitting instructions for the competent owner to fit. The Type 9 Sierra gearbox is not part of the kit but is either supplied by the owner or can be supplied with the kit by Hi-Gear Engineering Ltd.

The vehicle speedometer will need recalibrating. Several companies are able to do this. Instructions on how to measure the vehicle speedometer characteristics for re-calibration are included.

The Kit Comprises

  1. Cast aluminium Bell Housing
  2. Clutch release lever pivot & bolt
  3. Gasket, Bell Housing to gearbox
  4. Extended spigot bush
  5. Rear rubber gearbox mounting
  6. New gearbox support crossmembe
  7. Modified gear lever assembly, precision short shift
  8. New propshaft assembly
  9. Speedo cable/circlip
  10. All bolts & fasteners
  11. Detailed fitting instructions
  12. Loctite (2 types)

The Bell Housing is cast in high-strength LM25TF heat treated aluminium alloy and is robustly constructed. The standard MGB clutch cover, release lever and clutch operating hydraulic cylinder are all re-used. The standard MGB clutch driven plate and release bearing are used with the kit.

A precision short-shift gear lever is supplied which puts the gear lever in exactly the same place as the original so the conversion is visibly undetectable.

The MGB gearbox supporting cross member is replaced by a stronger stiffer crossmember stressed to take all gearbox loads and engine restraint loads due to acceleration and braking.

Gear Ratios MGB Standard Ford Modified Ford Closer Ratio
First 3.44 3.65 2.98 3.36
Second 2.167 1.97 1.97 1.81
Third 1.382 1.37 1.37 1.26
Fourth 1.0 1.0 1.0 1.0
Over-Drive/Fifth 0.82 0.82 0.82 0.825

The resulting performance is similar to driving a modern car with precise control of the gearbox, well suited ratios producing relaxed driving with driver confidence.

Other gearbox ratios can be supplied to suit the vehicle application.

The propeller shaft provided in the kit is to the original manufacturer's specification:

Torque: 570 Nm, 422 lbft (short duration) MAXIMUM
Speed: 7000 Rpm MAXIMUM.

This corresponds to 5740 engine rpm in fifth gear (ratio 0.82:1) and 7000 engine rpm in fourth gear (ratio 1:1). For any higher values of torque or speed, Hi-Gear Engineering Ltd can refer the customer to the manufacturer.

Kit Price £1125.00 Plus delivery, packing and VAT @ 20%

For more information on our gearbox conversions for classic MG cars
Call Hi-Gear Engineering Ltd on Tel: 01332 514 503

Suppliers of Five Speed Conversion Kits to:


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