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When sitting and riding on mountain bike, front gears will not shift.
#1
Hi, first post, very noobie to bike stuff sorry :)
(Sorry, it's a little long, tried to keep it concise, sry).

Basically, when the bike is on a stand or even just picking the bike to rear tire is hovering, when pedaling and shifting through the front gears 1,2,3 it shits perfectly. Very smooth and fluid. However, when I'm riding the bike the bike gears will not shift at all!

(Quick necessary back story). Original issue was that the chain was rubbing against front derailleur, took it to Halfords said the FD was bent. (No clue how that happened, don't recall dropping the bike or anything bashing in to the FD). The Halford's guy simply bent it bake he said. (Whether that bent fixed FD is the issue still I'm not sure). So they fixed that and all but everything seemed fine for a while until the FD gears were not shifting anymore when sitting on it. Halfords wouldn't of noticed that because they don't ride it themselves after fixing.

So I changed around a bit with the HL screws attempting to fix this issue with instructions from YouTube vids. Only with adjusting those screws (haven't adjusted the gear wire yet). I've more or less fixed it except for the 3rd gear. So 1 shifts to 2 nicely, issue is that the grip shift on the bike, the arrow doesn't align corresponding to the gear..

Grip shift, arrow pointing on 1, chain on gear 1.
Grip shift, arrow pointing (one click above) 2, then the chain goes on gear 2. (So essentially being between gears actually shifts it to the second gear).

When the grip shift is on 3 the derailleur does move and so does the chain, but it just doesn't grab on to the largest crank. (Similar issue with grip shift indicating like on 2) when on 3, it clicks past it once more, then sometimes it goes in to 3. But it's not very smooth at all and probably gonna damage the cranks or something.

Summary (With a bent FD that has supposedly been fixed by bending it back remember):

Front bike gears shift perfectly WHEN NOT sitting on the bike. (However, the grip shift numbers don't align 100% with gear 2 and 3).

WHEN SITTING on bike, FD gears were not shifting at all, adjusted with HL screws 1 and 2 shifting proper. (Still with the grip shift number not 100% aligning properly with the actual chain on the gear).

Will not shift to the 3rd gear at all when sitting on the bike.

Thank you for taking your time for reading all of this :)





       
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#2
A little tough to diagnose.
When you say that it "won't shift", does the derailleur push the chain up against the bigger chainring, but it just won't make the jump? Or is something (or nothing) else happening?

It's not uncommon for a bike to shift better in the stand than on the road. You have much more force and tension on the chain when you're actually riding it and that makes it harder to shift. Here's a couple things:
- It could be that the derailleur is still too bent to work well. Sometimes you can't bend these back well enough as their shapes are actually fairly complicated. Maybe need to replace.
- It could be the derailleur now has a lot of flex in it after being bent back and forth. So it looks ok, but bends under load and doesn't shift the chain well.
- Could be the derailleur alignment and/or adjustments are off. It being even a couple of degrees off of straight or a couple millimeters too high or low can really affect shifting. Adjusting the HL screw should have had zero impact on how well it shifts to the middle chainring. Maybe you just need some cable tension adjustment too?
- Could the cable be misrouted? Derailleurs are very sensitive to the cable being attached in the right position
- Could be the shifter is damaged or a split in the cable housing somewhere

If you can't figure it out quickly, I would take it back to the shop and say that it works fine in the stand but not on the road. They should test ride it for you. You may or may not get out without paying them something. But they should be able to find it.

(pics and/or videos never hurt if you want more advice from us.)
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