Red Caboose GP-9 Rebuild

I was surprised to find that no one has ever actually documented a Red Caboose GP-9 rebuild. Now lots of folks know that P&D Hobbies makes a repower kit, some don’t. Also some, but not many, know that Des Plaines Hobbies makes a brass frame for the Red caboose GP-9. So, I’m going to show how to rebuild a Red Caboose GP-9 here. It does not require any power tools other than a drill and a soldering iron. I’m also going to add DCC with sound.

What You’ll Need…

• Des Plaines Hobbies, #OSA1055 GP9 Brass frame, $30.
  
• P&D Hobbies, #2200K, GP9 repower kit, plastic trucks, $165, or #2201K w/brass trucks, $240
  
• MRC #1818 G/O DCC sound decoder, SD45/MP15, ~$75 online
  

Disassembly

Remove the body from the frame and it should look like the photo. Remove the lighting board. If you are going to keep the Geep running on straight DC, keep the board and lamps because they are 1.5 volt bulbs. If you are going to add DCC or DCC with sound, you will need 12 volts bulbs for the lighting.

Remove the four Phillips screws from the top motor mount. Pop off the motor leads and save them for later. Remove the mount and then lift out the motor.

You will now see the bottom motor mount. There are 5 screws holding the mount in place. Two of the screws also hold the air tanks to the bottom of the frame. The other 3 screws hold the fuel tank in place. Remove all 5 screws.

Flip the whole chassis over and remove the coupler mounts. These are what hold the upper deck to the frame. Remove the deck and set aside. You now have a naked chassis. The fuel tank and air tanks may need to be popped off the frame if they don’t just fall off. Save the frame because you are going to need the coupler mounts and also use it to make some measurements.

Prep for Speaker Install
I’m going to add DCC with sound and will put the speaker in the fuel tank. If you are sticking with straight DC or not adding sound, skip down to the new chassis assembly.

Pop open the fuel tank and remove the steel weight.

Make room for the speaker by removing the center stud. Lay the speaker in the tank bottom and trace around it.

Drill holes in the bottom of the tank inside the traced circle. I used a 1/8” bit.

I made a grille for the speaker out of a nylon stocking. This is to keep out ballast and small birds. Lay a piece of the stocking in the bottom of the fuel tank and paint it with liquid cement. It will immediately stick to the tank. I used two layers.

When that is dry, make some baffles around the speaker as shown and cement in place. On this model I filled the tank with BBs and a lead weight from an old HO scale engine. I also filled in the top of the tank over the speaker with BBs and cemented a styrene cover in place. The BBs are kept from rolling around with a liberal dose of CA. On a previous rebuild I used tungsten chunks but then I had to rework the top of the fuel tank. This rebuild uses the stock tank top. The weight of the lead, BBs and speaker is more than the steel weight alone so you’re not losing any traction with this setup. Drill out the hole in the tank top where the mounting screw passed thru for the speaker cable. I found that a 3/32” hole was just about a perfect fit. Install the tank top and set it aside.

Assemble the Chassis

Mount the bolsters from the P&D repower kit to the brass frame with the 2-56 self tapping screws provided by P&D. This is my second rebuild. The first one went without a hitch but the mounting holes in this frame did not line up perfectly with the holes in the truck bolsters. I’ve heard from other people who’ve had the same problem. To fix this, drill out both mounting holes in the frame with a #38 bit (0.101”). This will allow you to set both screws in the bolster and keep them centered on the frame. The bolsters go on the top side of the frame with the boss facing down and the screws go in from the bottom. You are looking at the bottom of the frame in the photo.

The brass frame lacks any detail and when I rebuilt the first GP9 I noticed a lot of “air” between the frame and trucks that wasn’t there with the plastic frame. That’s because the frame rails are absent from the brass version but they can be easily added.

Mark the locations of the fuel tank and air tanks and scribe a mark across the frame. Now cut four lengths of 1/8” Plastruct “L” angles to fit from the tank lines to the ends of the frame (see photo and note the angles were placed on the wrong side [top] of the frame). Now scribe a line 1/2” in from the edges along the frame length. CA the angles facing inward along this line.

Cut 8 strips of 0.020” x 0.156” styrene a bit over 1/2” long. Using the old frame as a guide, CA these gussett strips perpendicular to the Plastruct angles. When the CA is set, trim flush with the frame edge and file at an angle from the outer edge to the angles. Now when you mount the power trucks you won’t see “air” thru the frame.

Drill out the hole in the center of the frame so the speaker cable can pass thru and do the same for the lower motor mount. Remount the fuel tank and air tanks with the lower motor mount and screws you removed earlier. Leave out the center screw.

Drill a 1/8” hole in each corner of the lower motor mount. The power leads from the tucks will pass thru these on their way to the DCC board.

Mount the power trucks per the instruction sheet and thread the power leads on the back side of the bolster.

I used vinyl electrical tape to hold the leads to the frame and fed the wires thru the motor mount.

This is the trickiest part of the assembly, putting the cross shaft in the U-joint yokes. They look like they can’t possibly fit but they do if you are patient. Also, the cross shaft has a tendency to fly out of the pliers, so be prepared to look for flying cross shafts because you don’t get any extras. Once one side is seated, seating the second side is a snap, literally.

Drill a 3/32” hole in the top motor mount for the speaker cable and power leads. Set the motor in place in the bottom motor mount and connect the drive shafts to the power trucks per the instruction sheet.

I spliced the two black power leads and two white power leads together and covered the splice with heat shrink tubing. This was there are only two power leads going up to the DCC board.

I threaded the speaker cable and power leads thru the hole in the top motor mount and screwed the mount in place.

You can now wire to the motor directly if you are planning on using straight DC, or you can wire directly to a DCC board that will fit on top of the motor mount. The MRC unit is a bit larger so I wired in a four pin connector. The two outer leads and power pickup from the trucks. The two inner leads go to the motor. With jumper pins in place I tested the unit of straight DC to make sure it ran smoothly. I’ll make a four wire harness to connect to the MRC DCC board that mounts in the GP-9 shell.

Time to test fit the deck over the brass frame. Make sure the power leads do not interfere with how the deck seats to the new frame. Salvage the coupler box mount from the old frame and install it to hold the deck to the new brass frame.

Now is also the time to add additional weight to the chassis. Photo 28 shows tungsten chunks. Tungsten is more dense than lead but it is expensive if you have to buy it. Photo 29 shows lead weights added. I added almost 2 pounds of weight between the speaker, BBs and lead.

Place the body on the chassis and leave off the dynamic brake blister (or the hood filler if your unit does not have dynamic brakes). Slide the MRC DCC board into the body shell aft of the opening and hold it in place with a couple fingers. Flip the shell over and lay in some styrene strip to make a pair of rails for the decoder to sit on. I used 0.060” x 0.125” strip held in place with liquid cement. Photo 31 shows the view from the top with the brake blister installed. With the board up here, you can easily attach the headlight and backup light leads to the board, plug in the speaker and the power/motor leads with the brake blister removed.

Finish the kit per the Red Caboose instructions, paint and letter as desired. Photo 32 shows my previous conversion model. One down, one to go!