J-Type Marine Gearbox™

J-Type Marine Gearbox™

A popular Marine Gearbox found in Freeman Cruisers, Birchwoods and Camper & Nicholson 32.

J-Type Gearbox™ Spare Parts

Sheridan Marine still manufacture the majority of J-Type gearbox spare parts and can offer servicing and repairs. There is an owners handbook available which contains general servicing information. Once you have the manual there a helpline after 4pm on most days. Once the problem and remedy has been decided the relevant parts can be dispatched by post or collected from Sheridan Marine directly.

At Sheridan Marine we have a dedicated J-Type Gearbox maintenance facility where we disassemble and rebuild gearboxes as required. We then test run the gearbox prior to collection or dispatch.

J-Type Gearbox Types

Inside a J-Type Marine GearboxShown is the standard J-Type Gearbox with the Mark 2 2:1 reduction, often seen on the Nic 32 and Birchwoods. This version may be water cooled. Often the reduction box is rotated to the starboard side, at the 3 o'clock position, this configuration is often found on Freeman Cruisers. The J-Type Gearbox is also available as a direct drive version where the output shaft is in-line with the engine's crank shaft. The earlier Mark 1 2:1 reduction is identified by it's pear shape, some of the earliest boxes are known as the C3.

Over the years there have been variations and modifications to the internal workings of the gearbox, it is therefore important to identify accurately your particular requirements when servicing your J-Type Gearbox.


There are a number of regular maintenance jobs that should be undertaken on your J-Type gearbox.

  • Changing the oil regularly - Engine Oil is required, preferably SAE30 - NEVER use EP90 gear oil.
  • Occasionally the clutch plates need tightening as they are not self adjusting.
  • The reverse band also needs adjusting as the lining wares - Exchange brake bands are available if required.

General maintenance issues are described in the J-Type Handbook along with exploded diagrams of the internal workings.

History of the J-Type Gearbox

The J-Type Gearbox was produced in the United Kingdom by WaterMota. Production of the spare parts has since passed to us at Sheridan Marine where we still continue to manufacture spares and repair existing gearboxes.

The original J-Type Gearbox was developed from the American JOES Type 505B Gearbox, Mr Walter Fair, and later his son Colin Fair originally imported parts and assembled the marine gearbox at their works in Walton-on-Thames.

The original gearboxes were sealed and driven by a dog shaft drive from the flywheel, these early gearboxes feature four foot mountings. It could therefore be adapted to be driven by almost any engine, this was it's main selling point. In 1911 they moved to a garage in Newton Abbot, Devon, production came to a halt during the First World War when the factory was commandeered for the war effort.

When the E93A Side Valve Engine was produced by Ford, a special version of the JOES Gearbox was manufactured to suit, this was known as the C4, which we still see today.

In the early 1950's the 105E, 109, 115 and 122 Ford Engines were brought in and the J-Type Gearbox took it's present form and has since been used in many marine installations.

In 1968, at much the same time as Ford introduced the Crossflow Engines, the J-Type Gearbox underwent a 'modernisation', mostly a strengthening process, the main shaft for instance went from 7/8" to 1" and the casings became die cast instead of hand forged. This had the effect of changing many of the part sizes and numbers. Unfortunately there is only one handbook so careful selection is required when ordering parts.

WaterMota Engines & J-Type Gearboxes - Find Out More

For more information on WaterMota Engine and J-Type Gearbox spare parts please phone us.