The T 3s had a wet steam engine with two cylinders that drove the centre coupled axle.

The water supply was stored in a well tank between the frame under the boiler; the coal bunkers were on the left and right hand side of the firebox.

The springs on both front axles were linked with equalising beams located above the running plate.

The early T 3s did not have a steam dome, but were equipped with a regulator housing on top, from which the admission pipes led directly to the cylinders outside the boiler.

Later batches (from 1887) had a steam dome, and the admission pipes were located in the smokebox.

Due to the addition of the steam dome, the location of the sand box and sanders were changed.

The back wall of the cab was now straight and the lower section no longer sloped.

As a result, Class 89.75 ended up with a mixture of various locomotives types, in some cases with numbers that followed directly on from one another.