This is a project that I started at the beginning of 2020 so it’s about time I shared it with you. The Bachmann PCC Interurban Streamlined Car has been around since 1983 and was released in a large variety of paint schemes and liveries. However, all the models released up until about 2000, when Bachmann upgraded the chassis, suffer from the same problem; the white plastic gears on the axles crack. In this post I’ll share with you my 3D printed replacements to fix this.
The PCC Interurban Streamlined Car, and similar Brill Trolley released the year before, share a similar chassis with the same trucks. The body is all plastic and clips over the metal chassis, which fills the body.
The underside is fairly basic and you can see all four axles are driven via gears. These are the gears that crack under the pressure of the metal axles press fitted into them.
With the body removed you can see the chassis, which is made of two halves and separated by Bachmann standard fastener and washer system. Should these brake I’ve made replacements available here.
With the two screws removed the chassis haves come apart and the trucks fall out, although the repair can be done without separating the chassis or removing the trucks if you wish.
The large drive gear in the centre of the truck doesn’t have any issues.
The wheels have a short axle which press fits into the gear, when fully inserted the two axles do not touch each other so the gear also forms the electrical isolation. The wheels should just pull out. If the gears are cracked they’ll come out very easily.
The original gears, as shown on the right of the photo below, are made from a material that’s prone to cracking and you can see the light change as it hits the crack in the gear. With the metal wheel inserted the crack opens up. This causes two issues; firstly the spacing between two of the teeth is larger than the rest and causes a bump as the gear turns or jams the other gear. The second issue is there is little friction between the gear and the axles so the gear may turn, but the wheel won’t.
3D printing a set of four to replace all the gears is the answer and given the small size of these gears, roughly 5mm (0.196″) diameter, the best material is Shapeways Smooth Fine Detail because of its accuracy and hard-wearing properties. All four have been printed on a sprue so they don’t get lost in the printer.
Unlike injection moulding the sprue doesn’t actually touch the gears, it just passes through the hole in the middle. This can easily be cut with side cutters and the gears are ready to use, although I would recommend cleaning out the hole in the axles of any 3D print residue before you use them.
Refitting the gears and wheels is fairly simple. Position the new axle gear inside the truck and lightly push the wheel axle through the hole in the truck and into the gear. With both wheels lightly fitted, press the wheels together to press fit them firmly into the gear, just don’t push them in too far. The inside distance between the back of the wheels, commonly known as the Back-To-Back dimension, should be 7.65mm (0.301″).
Even if only one of your gears is cracked I would recommend changing all four as it’s probable the others will crack once you start using it again.
And that’s it, the street car is ready to use. The set of four gear axles can be found here.
I have several new gears for different loco types and scales to share with you over the next few months, but if you have something that needs a gear, get in touch. Just like this project I started last year, I may have all ready done it!