Description of the Montmirail-type tractor (Series 851 to 852 and X to Y)
This model was a compromise of the Indre-et-Loire 13-15 series, from which it had received the cabin and the aft cowl, and the Vendée, from which it had inherited the forward cowl. However, ramps with a return to the front had been installed on the engine inspection platforms. Skirts with indentations towards the front and rear had been installed on each side of the chassis. The first axle had been moved slightly forward to improve stability and reduce the overhang aggravated by the increased weight of the new engine being used.
Tractor Y was built according to a different layout. The cab had been moved aft and a very long hood housed the engine, auxiliaries, and fuel tank. The skirts had been removed. The reason for this new design was the installation of a coupling system for the simultaneous control of two units. In this case, the two cabins would have been placed face to face to reduce the length of the connecting cables. In fact, this option, which was also available for the X tractor, was hardly used by the destination network, and only two examples built for the Têt mines used this possibility. However, this experimentation was at the origin of the realization of the machines of the type 400.
The tractors were uniformly painted dark green. The vermilion red front and rear crossmembers were yellow with the company logo and engine number for the Seine-et-Marne units, the letters X on either side of the central stamp for the third and Y for the fourth.
On the first three, a rectangular plate bearing the initials C.F.D. had been fixed on the skirts, in line with the shelter. On the Y, this plate had been attached to the sides of the cabin.