Salamanca was also the first rack and pinion locomotive, using John Blenkinsop's patented design for rack propulsion. A single rack ran outside the narrow gauge tracks and was engaged by a large cog wheel on the left side of the locomotive. The cog wheel was driven by twin cylinders embedded into the top of the centre-flue boiler. The class was described as having two 8"×20" cylinders, driving the wheels through cranks. The piston crossheads slid in guides, rather than being controlled by a parallel motion linkage like the majority of early locomotives. The engines saw up to twenty years of service.
It appears in a watercolour by George Walker (1781–1856), the first painting of a steam locomotive. Four such locomotives were built for the railway. Salamanca was destroyed six years later, when its boiler exploded. According to George Stephenson, giving evidence to a committee of Parliament, the driver had tampered with the boiler safety valve.
Salamanca is probably the locomotive referred to in the September 1814 edition of Annals of Philosophy: "Some time ago a steam-engine was mounted upon wheels at Leeds, and made to move along a rail road by means of a rack wheel, dragging after it a number of waggons loaded with coals." The item continues to mention a rack locomotive about a mile north of Newcastle (Blücher at Killingworth) and one without a rack wheel (probably Puffing Billy at Wylam).