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I need to replace both of the shifters on Giant Rainier MTB.

It has Shimano Deore LX rear derailer (mega drive) & Powerglide2 34T 9-speed cassette ~ Deore SL-M510 Trigger Shifters, (now wholly torn apart, useless, and non-rebuildable) ~ Shimano Deore front derailer w/ 44T 32T 22T chainring.

My question asks: What model shifters may be used to replace the original shifters? ...or must I use the exact SL-M510 shifters.

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Any 9 speed Shimano-compatible shifter will work (most 9-speed shifters are Shimano-compatible, the only exception I'm aware of is Microshift Advent).

Currently, 9-speed is only available in entry-level ranges (the highest at this stage are SL-M3100 Alivio, so you'll loose some features - mostly the possibility to actuate the downshift lever with the thumb).

Note that if you want to stay within the Deore range, there is still the option of using trekking components (the closest "modern" equivalent of what your bike has). These are 10-speed (Deore T6000 and XT T8000), so it would require to change the rear derailleur, the cassette and the chain as well (you can keep the chainring and front derailleur). The cassette and chain being wear items, the only "real" replacement in this scenario is the rear derailleur. But I have the impression that this range is being phased out, so components may be hard to find.

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Your bike has a triple crankset and a 9 speed cassette.

That's pretty much all the details you need to match in your new shifters.

What style you choose is personal preference, but they have to suit your flat-bars, so no road-bike brake/shifters.

I personally prefer to keep components separate where possible, so I would avoid flat-bar shifters that have integrated brake levers. Sure they save space on your handlebars, but break one and you have more to replace.

Do take the opportunity to fit new inner gear cables; it is barely any more work and a nice smooth end is easier than reusing the old ones. Evaluate the outers too - now's the time if they need doing.

Your bike is not new - it could be a waste of money to drop new high end shifters onto it. Any of the middle groupsets would be more than adequate, like alivio and altus and acera. Tourney would work fine too despite being the "lowest" groupset. You could put Deore on, for completeness if nothing else, but XT or XTR or the other high end groupsets would be a bit pointless.

Do note that GRX will not work, that's a newer groupset that meshes road and MTB values and likely won't shift well if at all and doesn't have a 9 speed.

Check out Ebay or craigslist or your local recycling outlet - its possible you could get an entire donor bike for less than the cost of new shifters.


Another option is to go to a 10 speed groupset, if the costs work out for you. There's more to replace, so it might be too expensive unless you have a donor bike.

  • Cassette
  • Chain
  • Rear Derailleur
  • Right hand shifter for 10 speed
  • Left hand shifter for triple crankset.

You should be able to leave the front derailleur alone. The existing hub on the wheel will take a 10 speed cassette unmodified.

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    GRX won't work: road based, 10 or 11 speed, hydraulic disc brakes only, and only available for drop handle bars (the OP has a MTB)
    – Renaud
    Jul 14, 2023 at 7:09

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