In 1973 The Bonneville is increased to 724cc then later that year to 744cc, renamed T140. Trident T150V gets 10-inch front disc brake. X-75 Hurricane model built from Trident for US market. The Tridents are built at Small Heath alongside the BSA Rocket Three. An experimental 1,000cc four-cylinder Triumph nicknamed the Quadrant was built this year, but it came too late to help the company. It was made mostly from existing stock parts, mainly Trident. Without warning, in September Triumph announces the closure of Meriden works effective February, 1974. Of 4,500 employees, 3,000 are to be let go.

Faced with unemployment and having their products handed over to a rival firm, the workers rose up. This immediately starts an 18-month employee 'sit-in' and the closure of the Meriden plant. By late 1973, all models except the T120 are discontinued. In 1974 the newly-elected Labour government announces the formation of the Meriden Motorcycle Cooperative under the supervision of Tony Benn, and gives the group a 5 million pound grant. The following year the T150 becomes T160, restyled with an angled engine and improved frame. Other modifications include front and rear disc brakes, electric starters and left-hand gear changers. A total of 27,480 Tridents would be made in its seven-year life. In 1977 the limited edition Silver Jubilee T140V is made to commemorate Queen Elizabeth's 25 years on the throne. The Silver Jubilee is a T140 Bonnie with cast alloy wheels and special finish. 1,000 for UK, 1,000 for the US, and about 400 more made for export later. In October 1980, the British government writes off £8.4 million owed by Triumph, but still leaves company owing two million to Britain's Export Credit Guarantee Dept. The following year saw the production of T140 Bonneville Royal which celebrates marriage of Prince Charles and Princess Diana (only 250 made. It had electric start and a chrome fuel tank). The government waives the Cooperative's debt and allows the group to become a limited company with the workforce as its shareholders. Another model, the TSS was introduced, but it was too late to save the company. In 1983 production of Bonneville was discontinued at Meriden when the firm went into liquidation in the autumn. The company is sold to a property developer called John Bloor who is interested in the Meriden factory site for redevelopment. He rescues Triumph by buying the name and manufacturing rights.