Over the next decade, Lambert substantially refined the vehicle, with modifications including an additional wheel, a more powerful engine, and a new transmission system.

[3] The operator of the Union automobile controlled the steering wheel with his right hand and the speed-changing lever, which allowed two speeds for forward movement and one for reversing, with his left.

This novel transmission system, which was connected by double chain to the rear wheels, was gearless, eliminating the jarring movements then associated with gear changes.

Started by dry cell batteries, the four-cycle gasoline engine had two opposed cylinders that produced an initial eight horsepower.

[3][7] The final model produced by the Union Automobile Company was a 1905 Model E. Fitted with a detachable side entrance tonneau body, which sat three people, the car was upholstered to a high standard: genuine leather was used in combination with a soft insulation material and springs in both the seat cushions and the back.

[9] It could hold up to five passengers, and was equipped with two oil lamps, a horn, and necessary maintenance tools, for a total price of $1200 ($40,693 in 2023) ($1125 without the tonneau).