By Bob Ward
Drive shafts are a feature of many slot cars in use today. In this article you will learn what you need to know about them.
The front-motor in-line motor/chassis arrangement has become fairly common since the slot car racing renaissance beginning in the 1990s but it really got started back in the 1960s. The purpose was the same then as now – to allow a deeper and more detailed interior than just a flat tray with a driver figure. Strombecker, a prominent manufacturer at the time, had front-motor cars as early as 1960, but these cars used a piece of rubber tubing to couple the motor to the drive shaft. Later versions used a very long one-piece motor shaft that ran all the way to the rear axle. Before long Strombecker moved to rear-motor inline designs and front-motor cars disappeared for decades. However, with the introduction of strong neodymium traction magnets in the 1990s they made a comeback and have been quite successful on cars for plastic sectional track with steel contact strips. Fly has used the arrangement in all its models of front-engine cars. Scalextric uses it in models of 2-seat front-engine sports cars to make possible the fitting of a full interior. Revell-Monogram and MRRC have also made extensive use of it. The chassis of two front-motor cars, a Fly Ferrari GTO and a Scalextric Dodge Viper, are shown above.
The front-motor arrangement seems at first to be an unlikely drive train configuration for a slot car, since it places the motor’s weight at the opposite end of the car from where it’s needed for maximum cornering grip. That flies in the face of proper principles of weight distribution for optimum handling. But with a stout magnet at the rear providing downforce the arrangement becomes viable. If you want to race non-magnet, however, you will do better to run a rear-motor car or convert your front-motor car to a rear-motor configuration. That kind of conversion, by the way, is not hard to do on a plastic chassis. All it really takes is a few basic hobby tools, a piece of sheet styrene or ABS, and a bottle of CA glue.
All the Fly, MRRC, and Scalextric front-motor cars use very much the same endbell-drive motor and drive shaft assembly. The difference from one car to another is only in having a longer or shorter drive shaft length and sometimes different connectors on the ends of the lead wires. The motor, shaft bushing, pinion gear, and spring coupler are interchangeable on all of them, as are the various mounting points in the chassis. (Drawing 1) Thus, if you have any Fly, MRRC, or Scalextric motor and drive shaft assembly you can use it in any of these manufacturers’ cars or in a scratchbuilt or kitbashed car using one of their front-motor chassis simply by lengthening or cutting the shaft as necessary. Since the shaft diameter on every motor currently being used in 1:32 scale front-motor home racing cars is .078” (2mm) you can easily and inexpensively make a longer shaft by getting a piece of .078” steel wire from the K&S metal rack at your local hobby shop and cutting a length to fit your car. In a Fly, MRRC, or Scalextric front-motor car you can use any endbell-drive Mabuchi S can (FC130) or other motors with the same external configuration. The motor will fit the chassis and the drive shaft and spring coupler will mate up with the motor’s shaft. In some cases, however, you may need to trim the motor shaft, either on the end that mates with the drive shaft or on the opposite end to clear parts of the chassis. This can be done easily with a Dremel Moto-tool equipped with a carbide cutoff wheel. Be sure not to let the motor shaft get too hot when cutting it, as this can damage the bushings.
Revell-Monogram uses the same arrangement but with a can-drive FC130 motor. R-M’s shaft bushing and pinion gear are compatible with Scalextric, Fly, and MRRC. Again, shaft length differences apply.
Removing the drive shaft from the motor and reconnecting it is not difficult, but many people have trouble getting the spring off without stretching it. The key is always to push the spring off the motor shaft or the drive shaft, as shown in Drawing 2, rather than pulling it. Place the jaws of your needle-nose pliers on the motor shaft between the endbell bushing and the spring coupler. Slide them along the shaft, pushing the spring coupler as you go. The coupler will normally come right off with only light pressure. Use the same technique to remove the coupler from the drive shaft as shown in drawing 3.
When it’s time to put the coupler spring back in place it just pushes onto the shaft. Fly and Scalextric motors have a splined shaft end to better grip the spring coupler. If you are installing a hopup motor from another manufacturer it may not have the splined shaft end and may not fit the coupler tightly. In that case, use a drop of medium CA glue in the spring coupler to hold it tightly to the shaft (Drawing 4). Don’t use the thin CA, as it can easily run into the shaft bushing and lock up the motor. Before using any kind of CA on a motor shaft or a drive shaft be sure to put a drop of oil in the motor and drive shaft bushings. Be careful not to get any oil where the CA glue will go.
You can use a gear puller to remove the pinion gear from a drive shaft assembly without removing the shaft from the motor, but you have to remove the shaft before you can press a pinion back on. Once the spring coupler is removed you can use a pinion press on the drive shaft exactly as if it had a motor around it. If you do a lot of gear changes you will save time by making up several shafts, each with a pinion gear with a different number of teeth. Whenever you put the shaft assembly back together don’t forget to put the shaft bushing back on before reattaching the drive shaft to the motor shaft.
One of the biggest problems with some front-motor cars is the drive shaft bushing’s tendency to pop out of its mounting in a crash or even a hard spin. When this happens the pinion gear starts chewing teeth off the crown gear and after that the car never has a smooth, quiet gear mesh. We have heard from customers who have glued or wired the bushing in place, but we don’t recommend either of those measures because they make the bushing difficult to remove when you need to. There’s a better way, as shown above in Drawing 5. All you have to do is cut a piece of styrene strip or basswood about 1/8” by ¼” and glue the end of it to the bottom of the car’s body, interior tray or tub so the end of it presses down on the shaft bushing when the body is in place on the chassis. It will take a bit of cutting and trying to get the exact location and length needed, but once you get it right it will permanently end all problems with the shaft bushing coming loose without making it hard to remove. Some front-motor cars come with an arrangement like this already in place.
With this information you should now be equipped to repair, replace, or modify the drive shaft assemblies on any of your front-motor cars with the fewest possible problems. Good racing!
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Copyright ©2014 Robert M. Ward. All rights reserved.