Pony Truck or Trailing Truck
For most of the photos on this page, you can click the image for a larger picture.
The "2" in the 4-6-2 Pacific locomotive wheel arrangement is the 2 wheel truck that supports the weight of the rear of the locomotive. This truck can be known as a
- Pony Truck
- Trailing Truck
- Delta Truck (as the weight is taken on 3 points)
The British Railways drawing use the term "pony truck" so that is the term used here. The Class 7 Britannia locomotives and the original Class 6 Clan locomotives were fitted with a leaf spring pony truck. This had limited room for movement and was reported to give a hard ride. The solitary Class 8 locomotive - 71000 Duke of Gloucester was fitted with a longer travel coil spring pony truck which is reported to assist in providing a very smooth ride. This pony truck was part of the drawing set for the lot 242 Clans.
We are grateful to Michael Hughes from the BR Class 8 Steam Locomotive Trust for the reproduction of the following photos which show the pony truck from 71000 which we will need to manufacture.
This is a view from the front of the pony truck showing the central front pivot. The triangular front section of the truck is a casting, the rear section is a fabrication.
This is a rear view of the pony truck. The coil springs are shown, either side of the outside Timken taper roller bearing axle box. The 2 oval plates are the weight bearing areas; 2 bolster cups "float" on here which engage with bolster domes fitted at the rear of the locomotive frames. Between the 2 plates is the centring pin. This pin is bolted to the dragbox at the rear of the frame extensions and engages in a slot on the pony truck. 4 side control springs (2 either side of the pin) control the movement of the pony truck on entering curves and help recentre the truck leaving a curve. The 2 oil boxes lubricate the centring gear bushes. You can see the end of the centring gear protruding below the oil box.