Plarail running issues on newly bought trains

Hello, I'm new here but I've been collecting plarail for a while now and recently bought a bunch of out of print trains still in the box. All the trains are near perfect quality but some have running issues when they go up or down a slope that I would suppose have to do with the gears since the tires are all good. As I've never really worked with the gears before, I was wondering If anyone could point to the exact issues and the best way to fix them without ruining anything. I have added videos of the types of issues I've encountered. 


1. https://www.youtube.com/watch?v=kSWOcwKyN5k
2. https://www.youtube.com/watch?v=SgkTbeHydG8
3. https://www.youtube.com/watch?v=w8pCNCoD4C4
4. https://www.youtube.com/watch?v=ILlUkka960c

I'd try checking the gear on the driving wheels first for any cracks, and if there are none you may need to open up the gearbox as the gear on the motor shaft might be slipping

You could use the Search facility here on BPT and type in 'split gear'.  You'll find lots of useful help that way. Looking closely at the gear on the driving wheel axle is certainly a very good place to start.

[Super]

I agree, exactly what Chrisjo and  Don9Doug say above. If these were all bought from the same fellow who bought them for his child they show the exact signs of a child holding the train still while running which will do something with any number of gears either spinning, splitting or cracking. The tell tale sign of an engine slipping on an incline especially slipping while pulling nothing is a cracked gear. What I am really curious about is the first video where the engine doesn't make it 'Down' the slope and looks like there is no slippage but the motor has cut out, don't recall this before. Is this the case?

BTW...welcome to BPT's ☺️

The upslope failures do look like classic split gear problems. The downslope failure/cutout could just be down to a precarious battery contact?  Make sure the battery is seated firmly and that the contacts on the battery and in the battery compartment are scrupulously clean.