Posts by John Lewis91

Dana Reyes5 said:you've made a mess of this and you're never going to get those gears indexed working if you keep at it like this.
the math regarding front tooth count versus gear count isn't quite right, but whatever
you should never, under any circumstances, set that front derailleur more than 5-7 mm above the largest chainring.
No matter how much you tweak that front derailleur, the chain shouldn't be jumping off the top of the big ring or dropping below the small one. You use those two tiny limit screws for that—they are limits, plain and simple. Once they're set, you don't touch them again. Everything else is just cable tension, whether you're turning the barrel adjuster on the derailleur itself or using the fine-tuning knob on the shifter.
At any rate, you've completely botched it, so go ahead and try resetting it all over again.

Thanks for the input, Dana Reyes5. What you said is technically true, but I already mounted a compatible 48T setup on my bike and it works fine, even if the build quality is nowhere near that Deore level. I actually put a Deore LX setup on a friend's Trek, and it runs like a dream for him... everyone's happy...🙂...even though I nearly lost my mind trying to install it on my own ride...
I trust you know your stuff... but honestly? I don't think even you could pull this off... unless you grind down about 1.5 mm from the bottom of the cage on this LX... just compare the shape of the bottom of the Deore cage against this 48T one when you're hanging out with the crew.

So, I just finished installing this Shimano Deore FD on my Trek.

If you're sitting there thinking about upgrading the derailleur on your old 21-speed bike, let me save you the trouble right now: don't bother. It’s a non-starter.😠

See, this Shimano Deore FD is designed for setups with 44-32-22T chainrings. Most 21-speed bikes run a 48/38/28 setup instead. What happens? When you try to shift into that largest front ring, the derailleur cage hits the teeth of the next one up. You could try to fix it by mounting the derailleur higher—maybe keeping the cage about 0.6 inches above the biggest ring—and sure, it might technically "work," but then you're asking for a chain to slip off during a shift. And trust me, having your chain jump while you're moving is a disaster waiting to happen.

I figured I’d post this just to save someone else from the massive headache.

Can I get some help from the experts here... or maybe just those who have messed this up before themselves?
I’ve got an MTB setup with a SRAM Rival Crankset (48/38/28) paired with a 7-speed Shimano Deore Cassette, 13-34 range—basically a standard 21-speed setup.

The rear derailleur is holding up okay, but my front Shimano Altus Component is absolutely trashed. It’s barely worth anything, but I can't get the indexing right for the life of me; it got bent during a crash and now shifting is a nightmare.

I have the chance to snag a Shimano Deore FD front shifter for free. According to the manufacturer specs, it isn't technically meant for this specific combination, so I'm wondering: will it actually work in the real world?
If anyone knows the answer, please share it with those of us still figuring things out. Thanks in advance!