Someone asked me recently why their Lionel train won’t slow down, and when I asked for elaboration, I learned the train wasn’t responding to the throttle on the transformer.
Usually I see the opposite problem, but this one is an easy mistake to make. Fortunately the fix for it is also easy.
This mistake is easiest to make on modern setups using a CW-80 transformer. The CW-80 has two sets of posts in the back: one labeled A and U and the second labeled B and U. The first set of posts adjusts its voltage output based on the throttle. The second set of posts outputs a constant voltage. Odds are when you connect the train to that set, not only does it run at a constant speed, but it’s a constant fast speed.
So the fix is to connect posts A and U to the track, rather than B and U. The B and U posts power things like lights, switches, signals, and motorized accessories.
On most transformers the U posts are all interchangeable if there’s more than one. But not all CW-80s are wired that way. It’s safest to use the U post directly below the A post. You won’t harm the train or yourself by using the wrong one, but it might not work right if you do.
If this happens with an older transformer that isn’t a CW-80, odds are you found some other set of fixed voltage posts. The train will work, but you won’t be able to control it. Vintage Lionel transformer had a varying number of posts and what combinations did what often varied as well. But generally speaking, you’ll almost always find posts labeled A and U. Those are almost always safe ones to use. If you want to get fancy you can use others. Refer to my collection of pinouts for Lionel transformers to determine what works best for your transformer.