Hi everyone.

I hope one of you can help me.

I have an issue with an old Maerklin FX locomotive from around 2000 (Diesel locomotive from the 29845 starter set). It has the motor equivalent to 60941. It hasn't run much (maybe 5 hours). When running it at low speeds (below about 50-60%) it runs smoothly. But when running at higher speeds it starts to jerk and runs unevenly reducing its speed temporarily every 50 - 100 cm's. The light on the train doesn't seem to dim when it happens.

I have tried the following:
- Cleaning the track.
- Oilling the locomotive.
- Checked the brushes.
- Running it on a track layout with no other locos on it.

I have also tried running it on a analog track, and here the jerkiness seems to set in at much lower speeds.

When running the locomotive on a rolling track in digital mode, it doesn't seem to happen nearly as much - not sure I can notice any jerkiness. Maybe because the motor doesn't have to content with hauling the weight of the locomotive.

I have other FX locomotives from the same time period (2000 - 2003), that doesn't exhibit that behavior on my layout.

Any ideas on what the issue might be, would be very much appreciated.

Another suggestion is to clean the armature 5-pole commutator, and remove any carbon dust that is trapped between the copper gaps (5 gaps to clean). Sometimes the carbon/graphite collects there due to long term use where the graphite is slowly rubbed off and collects there. Over-oiling also makes the carbon dust collect there.

Glad it worked.
I suggest you avoid opening the brushholder unless a real need as you may break the induction coil wires. This is something you do for heavy maintenance after long usage (200 to 1000 hours).
Tip: a cotton swab on which you remove most of the cotton allows you to clean the brush guide and collector without opening the motor.
Cheers
Jean