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I cleaned my wife's 1999-vintage mountain bike, and because no good deed goes unpunished, I seem to have caused a problem in the process.

This bike has a Shimano Deore 9-speed drivetrain with trigger shifters. Starting from the smallest cog, the trigger shifter for the rear derailleur can downshift through the first three gears correctly; after that, it needs to rotate back for the ratcheting mechanism to reset. That's where it goes wrong: the pawl apparently won't engage with the ratchet wheel, and the trigger swings freely.

I've been brave enough to remove the housing over the mechanism and blow some compressed air in there, which did not fix the problem. There are enough small parts in there that I'm reluctant to go further without some guidance (if it's possible for a home mechanic to fix at all).

I see that I can apparently buy a replacement for about $24, so if the correct answer is "replace it" I won't be too broken up.

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  • I like to lube such shifters, if balky, with a Teflon spray lube. Be careful of using any sort of lube which will leave a thick residue. – Daniel R Hicks Sep 30 '17 at 1:10
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    This is a very common problem with old trigger shifters. Sometimes fixable and sometimes not, but if it is fixable it's only going to require cleaning and lubing. – John Zwinck Sep 30 '17 at 1:32
  • "replace it" is the lazy way. Sure that will work, but there's a chance the rider will not like the newer one. – Criggie Sep 30 '17 at 2:30
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    I've had this happen on a number of shifters, both brifter and pod shifter. The main cause is aging of the lubricant which makes it thicker and gummy, stopping the pawl from dropping into the ratchet. So you need to clean the teeth, which means a solvent, then dry it, and re-lubricate before use. Fiddly and messy, but a lot more satisfying than outright replacement. – Criggie Sep 30 '17 at 2:31
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Get yourself some Clean Streak degreaser and a dental pick. Gently work the pawls until they snap back into place firmly. Then use the compressed air to clean it out and put a drop of thin chain oil onto the pivots. That should get you going.

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  • Would you advise OP to disassemble shifter as much as possible, or to work through whatever openings there are already? – Criggie Sep 30 '17 at 9:05
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    He mentioned that he had already removed the housing over the mechanism. I wouldn't go any further than that. – Noah Sutherland Oct 2 '17 at 23:46
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You can often do well by removing all the old sticky grease and re-oiling. Get off as much as you can with solvents and wiping, then flood with oil. I wouldn't use chain oil but the runniest general purpose oil you've got (even gt85/wd40). Clean off the excess and it should be a bit better. After using them for a bit, once again clean off everything you can and oil (I wouldn't use wd40 at this step, but a spray may be helpful, as might an oil with PTFE). I used 3in1 (once upon a time it was used as chain oil, but things have moved on since then); a light grease might also work its way in far enough.

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  • Motor oil and ATF fluid are generally a bit runny and messy, plus they can upset paint and tyre/brake rubber. Lithium grease works well for me in shifter mechs and it generally doesn't wash out. – Criggie Nov 12 '17 at 7:59
  • @Criggie I didn't think of motor oil mainly because it's so hard to apply in small quantities without decanting. And I suppose transmission fluid is an oil but I've never handled it. A very light grease might work nicely if you can get it in there; I used 3in1 oil at the last step, and it's served me a couple of years kept outside. I've just replaced that beater bike for [an unrelated failure] (bicycles.stackexchange.com/q/49589/7309) – Chris H Nov 12 '17 at 8:07
  • So what is GT85 then? I figured it was an 85wt diff/gearbox oil. – Criggie Nov 12 '17 at 10:44
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    @Criggie it's a light spray oil with PTFE. It penetrates well but carries on lubricating much better than WD40. I use it on the chain, cogs and derailleurs of that bike because it reduces surface rust left out in the rain. – Chris H Nov 12 '17 at 11:41

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