1990 Bianchi Sika

Right, another project. Can you swap the whole unit, or just some components?
One thing I noticed rebuilding 3-4 M900 units an others is that over the years Shimano changed things in small ways even between two separate M900 units, typically if nothing is broken inside all that is needed is a full strip down/clean/regrease as the original grease gets gummy and just needs a good flush, sometimes a WD-40 flush will fix the internals and no disassembly is required. More often than not it needs to come apart though.

ATBOY's youtube videos are invaluable, big shout out and thanks if you are on here! 😁

The first time I went inside the DX unit looking for parts I was only after a pawl with the sharp end chipped off, the DX part was identical, with this most recent rebuild I only needed the main support stem for the whole shifter internals. I try to keep the internal parts all original except for broken parts. Not necessarily to say they are any better but assume to will work well together as it's how Shimano designed that particular version.
 

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