California's Railroad to the U.S. 1861 - 1996

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Model Train Help EBook

Southern Pacific DD35

Building a HO Scale DD35 from Athearn and Kato parts

© Jean-Marie Syx of Belgium

Reproduction, Publishing or use of this text and images either in print or electronically are prohibited without the written permission of the author

The forward planning:

Have done some measurements and this is what I came up with:

  • Total length is 87 ft 11 ins this translates to 308mm. Mine will be 303mm and this means that the coupler box on the trucks is 1.5mm inside the walkway end. This is without the dropsteps.
  • Truck centers are 55 ft apart and this is the exact distance between the shell tabs. These tabs are also dead on where they should be, so I will leave them on until the new truck fixture is made and attached to the chassis.

The Project Begins:

The Chassis:

Remove both truck mounting tunnels. They are too wide to fit in the new Kato shell, which is only 18mm wide on the inside. By the way, a Kato motor is 17mm wide. A new W- shape part (see drawing below), 0.5mm brass – 12mm wide is formed by bending it to the right measurements. You have to file slots in the chassis in order to get a good fit flush with the chassis underside. This piece is fastened to the chassis with 2 countersunk M2 screws. Then you glue the styrene block to the brass and drill a 3mm hole right through the brass and styrene.

Now you must disassemble the trucks and widen the hole on top to 3mm or approx 1/8 inch. Slip a 3mm styrene tube into the styrene block and through the brass, letting it stick out just enough to get the truck on it. Put an M2 screw though the tube and fasten with an M2 nut. Please check truck play. This way both trucks are now in full electrical contact with the chassis. To avoid shorts if the chassis rocks from side to side, I glued 5 thou thick styrene on top of each truck sideframe.

Note: The styrene block doesn't have to be that thick. The reason why I gave it this thickness is that it was intentionally designed to get under the top truck clip = the worm cover. By using a screw for holding the truck to the chassis this styrene block could lose 2/3 of its bulk.

The Walkway:

I made it 1.5mm thick in a double layer. First a 1mm layer that will sit on the chassis and which is 1.5mm less than the overall length and width = 300 x 32mm. Against the outside edges a 60 thou x 80 thou strip is glued. This gives a side sill with a little recess and our walkway is now dead on right in length and width = 303 x 35mm. The second layer, 0.5mm thick is a little longer and wider and glued on top of the underlayer. By doing this, you can cut off excess material flush with the walkway edges.

Drilling dimensions for the stanchions: from the ends, first at 3mm, 14mm spacing, 9mm spacing, 7 times 14mm spacing and 2 times 9mm spacing. Mark it from left to right and right to left.

On the ends: mark at 3.5mm, 12.5mm, 22.5mm and 31.5mm. Drill with 0.7mm or 28 thou or a No.70 drill bit.

The rear pilot and steps are recovered from the Athearn shells and glued underneath the walkway at 6mm from the end of the walkway. It is possible that a little filling is needed. I glued a 3mm thick and 25mm long filler piece against the rear pilot, this way the shell is oriented on the chassis. Now the chassis can move about 0.5mm to either side.

Body Shell Construction:

From both Kato GP35 shells, the cabs are to be removed and the ends sawn off flush with the radiator grilles.

Make a square tube shaped filler piece, 17mm long and 10mm high to connect both shells together, and radiator sections facing each other. The remaining opening in both shells is closed with 1mm styrene sheet.

The front and rear ends are 21mm wide, 12mm long eand33mm high. I made these boxy shapes out of 1mm styrene and glued them to each end. Remember that before assembling this end piece you’ll need to cut out the opening for the Cannon door part no.1004.

Air tanks:

For the air tanks I took styrene tube, 4mm and 38mm long. Fill both ends with styrene tubing and or rod. File these ends ±half round, and glue them to the chassis with epoxy.

Battery box:

The toolboxes from underneath the Kato GP35 cab are cut up into 6 pieces and glued back together to a length of 32mm on a 1mm thick styrene, 32mm long and 7mm wide. Be aware to have 3 latches on each box. This assembly is glued under the walkway a little before the 8th. stanchion. At the back, and an additional 32mm x 8mm x 1mm thick styrene piece is added to give the box a little extra body.

Out of 30 thou clapboard you cut 4 pieces, 4 boards long x 2.5mm wide. File these until they are only 0.5mm thick and glue them in the middle between the latches against the walkway sill. Next to this box, on the right side comes a frame mounted bell.


On the underside of each end, and dead smack in the middle, there is a sandbox door.

At 2mm from the upper edge sits the headlight. Both headlight and sandbox door are recovered from the cut off rear ends of the Kato GP35 shells.


At the ends, you mark at 1mm from the left side and 2mm from the top the first grab. Following grabs are 5mm down each. On top there's another grab at 1mm from the left side and 5mm back from the end.

Final thoughts:

Although I envisioned this model to be powered, I will leave it unpowered for the time being. It seems like only a Kato motor or other small motor can fit inside the shell.

Otherwise this engine will never run on it's own. There has to be a lead engine in front of it.

This project was very intimidating at the start, but thanks to you Richard and your advice it worked out just fine.

I even would add that regardless of the hacking and slicing it wasn't that difficult at all, but hey who is not a little scared when placing the hacksaw on an otherwise perfectly good shell to make the first cut?


  • Railroad Model Craftsman, October 1963, Page 34. - Content unknown, probably UP though.
  • Prototype Modeler, February 1987, Page 40 - Content unknown, probably UP though.
  • Model Railroader Cyclopedia Vol.2 Page 153 - Photo of SP 8401.
  • Railroad Model Craftsman, November 1994, Page 77. - Modeling all 3 UP DD's inc. DD35.

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Sunday, 12 June 2005