The trucks are made using engineering plastic, rather than styrene, as it’s a harder plastic and better suited to the wear to which it is subjected by the axle ends. It just happens to be shiny. This is similar, for the same reason, to the plastic used for the gears of many of our locomotives - it stands up better to wear.
Engineering plastic is also used for handrails on many diesels, mainly due to its toughness and ability to bend rather than break.
For trucks and handrails, its main drawback is the fact that most paints don’t adhere to it all that well.
Since I backdated my layout, I no longer run diesels, but I always replaced the plastic handrails on diesels, using music wire in the original plastic stanchions - This combination was still rugged, but more-to-scale than plastic handrails at that time. Newer models have much finer plastic handrails, but that has made them more prone to damage.
Since trucks usually don’t get handled too much after a model is on the layout, paint will usually stand up well enough. I tried etching a few plastic sideframes using baking soda in a sandblaster, and it did remove the shine, and, I’d guess, helped the paint to adhere better. However, I couldn’t pick those particular cars out from the others, as most still retain their paint and weathering, too.
Adhesion promoters are available at automotive paint suppliers - I bought a spray can of it recently (fairly expensive) but I’ve not yet had occasion to use it. It’s main use is on exterior plastic body parts, such as bumpers and trim, so it may be a bit heavy for model use.
I’ve read that the paint for the polycarbonate bodies of radio controlled model cars will adhere to engineering-type plastics, too, and Pactra offers a number of colours in their “Racing Finish” line of paints. I’ve used it on some TrueLine caboose handrails and it seems to work okay, although those items aren’t subje
I was faced with replacing a lot of plastic wheels with metal. I found that many of my old, old Athearn sprung trucks were too flexible to work with the Intermountain wheels, and, like the OP, I had the problem with the Tyco/Mantua trucks that had no provision for wheel replacement. I decided to go with Tichy truck frames, which are plastic and work very well. I paint and weather the frames and clean out the bearings with a Truck Tuner. On some cars, it’s necessary to drill out the center of the truck so it will fit over the bolster pin. Then I either use a Kadee washer on the bolster if the coupler is too low, or shim the coupler draft gear box if the coupler is too high.
I am not finding any flat color options available from Pactra. Can you post a link?
I guess I am getting into the classic time vs. money question. If there is a type of paint that can be thinly sprayed directly onto the trucks and stick without a lot of advance preparation, I would like to try it out. If not, I may be more inclined toward replacing the trucks with something that looks better.
The Pactra paint which I mentioned was more in reference to handrails, and I used it mainly as a “primer” for a subsequent coat of PollyScale.
For trucks, PollyScale and Floquil (if you can find either) will work adequately (I still have a fairly good supply of the former, but am running out of Floquil).
I’d guess that Scalecoat (either I or II) will work, too, and it’s now available in flat finishes for some colours, notably several different blacks and in white, too.
Personally, I prefer Scalecoat I, and thin it with lacquer thinner, rather than the proprietary stuff. It may work for Scalecoat II also, as the formulae for the two paints are similar in make-up and vary mainly in proportions of the ingredients. With Scalecoat I, the lacquer thinner seems to shorten the drying time somewhat. I’ve not yet used it on trucks, though, so I can’t say how durable it might be - it is very durable on when airbrushed on metal or styrene plastic, though. As I mentioned earlier, once a car is on the layout, trucks should get little handling unless you have frequent derailments.
I have had good luck using rattle cans of Krylon Ultra-Flat Camouflage in two colors: 4292 Brown and 4293 olive. Where I actually want the trucks to be black I have used Ace Hardware’s house enamel “wrought iron flat black.” I have not had a problem with paint flaking off or attacking the plastic (Delrin for Athearn and Lindberg, but likely just styrene for cheaper trucks).
A very fine modeler named Mont Switzer uses a different approach - by using an aluminum oxide “media blast” in a special booth (and he does the work outside). He wrote it up in the NMRA magazine for May 2015 if you happen to have that issue: “Wood Meat Reefer Weathering.” The media blast roughens the plastic and makes it gray.
I use a wheel paint mask for painting my 33" and 36" wheels. Here is a link to the approprite page on the Walthers site
That’s similar to the baking soda method which I mentioned, but likely a little more agressive and therefore quicker.
I recently purchased a Paasche Air Eraser, which uses aluminum oxide as the blasting medium, and will be using it on the trucks of the batch of freights cars on which I am now working. There are 17 cars ready for paint (including the 6 Tyco/Mantua cars), with one Tangent tank car kit to be built, and 5 boxcars to scratchbuild.
During the winter, I like to have enough jobs to make it worthwhile to heat my paint shop, which is in a detached garage out behind the house. The room itself is quite small and heats up in no time, but the compressor, an oil-filled rotary type, needs to be warm enough to operate without overloading the circuit. Once it’s running, it keeps the room at a comfortable temperature.
We will all be eager to see you post the results of using the Air Eraser, Wayne. Switzer warns to use a dust mask and as he puts it “if you don’t think you need a mask, blow your nose after 10 minutes of media blasting without one. You will see for yourself the need for a simple dust mask.”
He also writes that the media blast creates the right gray-ish color but is very uniform in tone; it creates the perfect surface to hold Bragdon self adhesive weathering powders.
For my replacement Tichy trucks, I cover the axle bearings and bolster holes with small pieces of blue tape and spray them with brown or rust Krylon primer. Nothing special. The primer gives me a good surface for weathering with powders, and then I use a clear flat Krylon spray to seal those on.