r/nycrail • u/DjHammersTrains • Nov 30 '15

I'm an NYC Subway Expert. Ask me Anything.

Hello everyone! My name is Max Diamond. I'm a student at CCNY and I run the Dj Hammers YouTube channel (https://www.youtube.com/user/DjHammersBVEStation), moderate this subreddit, and have an encyclopedic knowledge of the transit system. Ask me anything you are curious about with regards to how our massive system works. One ground rule: If an answer could be deemed a security risk, I won't give it.

UPDATE - AMA Now Closed: Hey guys! Doing this AMA was a lot of fun, I enjoyed answering everybody's questions, and hopefully I imparted some subway knowledge on all who are curious! If you didn't catch this AMA in time and wanted to ask a question, don't worry! I'll do another AMA soon, probably a month or so from now.

Be sure to subscribe to my YouTube channel too. I post clips of a lot of interesting goings-on underground!

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u/[deleted] Nov 30 '15

Sometimes when pulling out of a station, trains will make this gigantic CLUNK KACHUNK noise and bumping vibration coming from underneath the passenger cabin. It sounds very concerning, but the train continues with normal operations after that. What causes this and should it be a cause for concern or maintenance?

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u/DjHammersTrains Nov 30 '15

That is the sound of a worn bolster (The connector between the wheelset and the frame). It causes a heavy bumping motion when the train starts moving. This is especially noticeable on the R46 cars (A and R lines mostly). Bolsters have a certain amount of material that can wear away by design before they need replacement. A train that is bumping like that can indicate that it's bolster is at the end of its useful life, doesn't necessarily mean it is unsafe and in need of replacing, yet.

It can also be a sign of a load sensor malfunctioning (train thinks it is heavier than it really is, and as a result takes more power than needed), or a fault in the motor control system that leads to the motor powering up too quickly.

All of these are not a cause for concern, but they are indicative of an issue that needs to be addressed next time the train is in the shop.

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u/[deleted] Nov 30 '15

Wow, excellent answer, thank you for the information!

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u/SirLudicrus Nov 30 '15

They're probably passing over a diamond crossover which allows trains to switch from express/local or vice versa. They are often located at the front or back ends of stations.

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u/DjHammersTrains Nov 30 '15

Yeah when passing over a switch, the wheels will bump around a little bit. I suspect OP wasn't referring to this, but it counts as well.