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Rear derailleur confusion here

Old 09-20-23, 09:01 AM
  #1  
juntjoo
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Rear derailleur confusion here

I've messed with all three screws and can't get it to shift to a lower gear. What exactly moves it inwards more? I even bent the frame a little in. It's been a while since I've had it running but before I was able to shift through all gears so idk what happened
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Old 09-20-23, 09:09 AM
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Okay, I've just confirmed that manually I can get it to shift into inner most position.

Should I use my hand or something to hold it in place while I adjust the cable?
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Old 09-20-23, 09:22 AM
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What shifter and derailleur? Two screws adjust limits. Once set they need to be left alone. Third screw is the "b" screw and is used to adjust the gap between the derailleur jockey wheel and the cassettes largest cog. None of the three are to adjust the indexing that your shifter transmits through a cable to the derailleur. Cable tension is applied to dial in alignment between derailleur and cassette.
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Old 09-20-23, 09:23 AM
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Limit screws only limit how far either way the DR can move. Usually you set them when you install the DR before putting the chain on. Mostly I think they are just to prevent you from shifting the chain off the cog on either side of the cassette. But if your bike is well adjusted, they really don't ever get used. They are there for a backup since your bike won't stay well adjusted all the time.

Which third screw were you messing with? The b screw is what position your jockey wheel to the cogs on the cassette. The Shimano RD's I use say to adjust it so the jockey wheel is close but not interfering (touching) any of the cogs when shifted to any position.

If you are talking about the barrel adjuster, then that is the one that positions the RD for the position selected by the shift lever. If you can't get in all the positions on the rear, then something is up with your cable binding somewhere. Or you just didn't tighten the pinch bolt on the cable in the proper place.
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Old 09-20-23, 09:31 AM
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Oh, this might be a problem...

I even bent the frame a little in.
Bike frame? The part the RD is mounted on? If your RD hanger got bent, then you probably need to get that checked by a shop or get a derailleur hanger tool and learn how to use it.
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Old 09-20-23, 10:00 AM
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Base of bike stand in super sharp focus there

There is no way you should be bending the frame to align the rear mech. What makes it move inward is the tension on the cable

You donít need to hold it in. Shift to the smallest cog. If it doesnít get there, open up the top limiter a bit. If the chain falls off, close up the top limiter a bit. Dial in the adjuster all the way on the cable entry (or shifter if applicable) then back it out 2 turns. Use a cable puller ideally or just pull the cable with pliers (but donít mash it) & clamp it. Shift up 2 gears and use the adjuster to fine tune the alignment.
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Old 09-20-23, 10:00 AM
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Originally Posted by Iride01
Oh, this might be a problem...

Bike frame? The part the RD is mounted on? If your RD hanger got bent, then you probably need to get that checked by a shop or get a derailleur hanger tool and learn how to use it.
Yeah, this is not good, at least as written by the OP. Maybe he'll clarify...
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Old 09-20-23, 10:02 AM
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Originally Posted by choddo
Use a cable puller ideally or just pull the cable with pliers but donít mash it & clamp it.
Cable puller is complete and unnecessary overkill. Pliers are fine; needle nose probably the easiest.
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Old 09-20-23, 10:03 AM
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Originally Posted by choddo
Base of bike stand in super sharp focus there
And either incorrectly tightened, or not tightened at all.
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Old 09-20-23, 10:04 AM
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Originally Posted by smd4
Cable puller is complete and unnecessary overkill. Pliers are fine; needle nose probably the easiest.
I like the gentle little nudge it gives the mech, what can I say
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Old 09-20-23, 10:48 AM
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Originally Posted by choddo
I like the gentle little nudge it gives the mech, what can I say
Better to nudge the mech, I suppose, than the hanger!
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Old 09-20-23, 11:17 AM
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Okay I'm getting closer. I lubed RD a bit and adjusted the screws again. I can never tell which is which. Idk how anyone does unless they're doing this for a living. Anyway, got it moving. I guess it was seized.

But now my chain looks short lol. I did take a couple links off cuz at first it looked too long with the RD hanging too far back. I'll put the links back on and check again.

I'm not sure what you're saying about the bike stand

And even though you explained to me the purpose of the 3rd adjustment screw i don't understand. As long as it shifts and doesn't make noise I'm good
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Old 09-20-23, 11:54 AM
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Your drive train needs more than "a bit" of lube.
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Old 09-20-23, 12:01 PM
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The B screw changes how the mech lines up vertically. So that when it’s in the big cog like there, the chain coming off the top jockey wheel has just enough room to line up nicely onto the bottom of the cog and go round. Too close or too far are both bad.


Yeah that does seem to need a bit more protection from water. The flaked off paint & rust just above the skewer suggests the frame has got bent there maybe. No mech hanger I think so maybe it’s taken a bash?

and actually, given that circular mark on the dropout there which looks like it's from the skewer clamp - is that wheel actually sat as high as it should be? You'll never get the mech aligned if it's not.

Last edited by choddo; 09-20-23 at 12:09 PM.
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Old 09-20-23, 12:15 PM
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go here and read before you do anything else to completely destroy what you are working on

https://www.parktool.com/en-us/blog/repair-help

https://www.parktool.com/en-us/blog/...eur-adjustment
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Old 09-20-23, 12:20 PM
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If that pic is with the chain in the big front ring, then you probably are still good on the chain length. If you push the RD cage forward towards the crank at the pulley wheel and it's at it's absolute forward limit, then you might need another link. Chain sizing just needs to be long enough for the Big/Big combo and not go slack in the Small/Small combo. Which on some 3x bikes BITD (long ago in the vintage days) with large differences in large and small ring, they would go slack and you'd be told not to use the Small/Small because there were the same or similar ratio in the middle ring.

Most manufacturers will say to size your chain by wrapping it around the Big/Big without going through the RD cage and then add a link or two. Some are different for 3x fronts. If you have mix and match components on your bike and have gone outside the specs, then you might not be able to size the chain properly.

The inner shifter cable looks like it might be shiny and new in the picture. Did you just replace it?

Last edited by Iride01; 09-20-23 at 12:25 PM.
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Old 09-20-23, 02:41 PM
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Begin at the beginning:

Lube the chain and DR pivots

[Your housing from the chainstay cable stop to the DR is a little short; the housing should be straight where it enters the DR. It's probably not bad enough to cause shifting problems, but if you want to be thorough . . .]

Sight from the rear and verify that the DR cage is parallel to the cogs

Open the chain if you have a quick-disconnect link, remove it, and move the DR through its range of travel; it should move smoothly with good spring tension. If you leave the chain on, set your shifter to the position for the smallest cog and pull on a length of bare cable and verify that the DR moves smoothly through its range. Verify correct chain length by shifting to the largest chainring and largest cog; the lower derailleur pulley should still be able to swing up at least another inch but not a whole lot more

Reinstall the chain if needed. With slack in the cable, try shifting to the smallest cog. If the DR doesn't move far enough outboard, relax the high-limit screw until it does

Pull on a length of exposed cable and verify that the DR will shift to the largest cog without throwing the chain into the spokes. Relax or tighten the low-limit screw if needed

With the chain on the middle ring and smallest cog and with minimal slack in the cable, shift to the next inboard cog. If the shift is sluggish or doesn't happen, use the barrel adjuster to increase cable tension until the shift is clean

Shift to the third largest cog and try shifting to the next largest and largest. Adjust your cable tension at both extremes, then verify that the chain shifts cleanly up and down all the cogs
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Old 09-20-23, 02:41 PM
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you are hurting your bike more than you are helping your bike.

DON'T BEND THE DERAILLEUR HANGER.. take it to a shop and have the DERAILLEUR HANGER STRAIGHTENED before you think you've "Fixed it"

i can visibly see the Derailleur is now Out Of Alignment in your pic.

and LUBE THE CHAIN, ok? Wow.

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Old 09-20-23, 04:03 PM
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Originally Posted by juntjoo
Okay I'm getting closer. I lubed RD a bit and adjusted the screws again. I can never tell which is which. Idk how anyone does unless they're doing this for a living.

I'm not sure what you're saying about the bike stand
The upper, higher screw is for the high gear, and the lower, bottom screw is for the low gear. That shouldnít be too difficult to remember. The higher gear is the smaller, harder to pedal one. The lowest gear is the bigger sprocket.

The comments about your bike stand is that you managed to get that part perfectly in focus. The rear derailleuróthe part we need to seeónot so much.

PS: +12 on lubing your chain.

Last edited by smd4; 09-20-23 at 04:50 PM.
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Old 09-20-23, 04:39 PM
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Originally Posted by juntjoo
Okay I'm getting closer. I lubed RD a bit and adjusted the screws again. I can never tell which is which. Idk how anyone does unless they're doing this for a living.
Move the derailleur in and out while looking at the threaded ends of the adjusting screws - the one that gets closer to the stop tab when you push the derailleur in is the low limit screw.
Originally Posted by juntjoo

I'm not sure what you're saying about the bike stand
The floor is in focus, the derailleur isn't. Probably not easy to see on a small screen.
Originally Posted by juntjoo
Focus is fine in that one, but the cable clamp looks incorrectly positioned.
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Old 09-20-23, 06:28 PM
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Originally Posted by grumpus
the cable clamp looks incorrectly positioned.
+1 and juntjoo you still haven't told us what make and model your derailleur is. Kind of important to know to give specific instructions for setup such as how to route the cable at the clamp.
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Old 09-20-23, 07:08 PM
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Originally Posted by Crankycrank
+1 and juntjoo you still haven't told us what make and model your derailleur is. Kind of important to know to give specific instructions for setup such as how to route the cable at the clamp.
Looks like an old Shimano RSX or similar.
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Old 09-20-23, 07:18 PM
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Originally Posted by grumpus
Looks like an old Shimano RSX or similar.
It's a Shimano STX, circa 1993. Positioned between Deore LX and Alivio on bikes like the Trek 930.
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Old 09-20-23, 07:19 PM
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Originally Posted by grumpus
looks like an old shimano rsx or similar.
stx.
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Old 09-20-23, 07:28 PM
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And the cable is routed wrong. It goes to the outside of the bolt, and that's the explanation.
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