How do I know if the front derailleur limit screws are doing anything?
 

When I adjust the front lower and upper limit derailleur screws, I don't see the bracket move. I know that my fidgeting with the screws does something, but I don't visually see the bracket moving. What am I doing wrong here? And how do I tell apart the lower limit screw from the upper limit screw?I am working on a low-end Shimano derailleur...Thanks!

The limit screws don’t move the derailleur cage, they limit how far the cage is moved by the cable. The best way to see this in action is by putting the bike on a repair stand and shifting the chain with the shift levers. If the chain doesn’t shift to the chosen chainring or if it shifts too far, then you need to adjust the limit screws.

This should help you sort out what you need to do:

https://www.parktool.com/en-us/blog/...eur-adjustment

They're called "limit" screws because that's exactly what they do ----- Establish the limits for travel. If the RD (or FD) were an elevator, the limits would be set so it can't crash into the roof or basement. However, for both elevators and derailleurs, the actual position depends on the cable they are hanging from.

On your bike, the easiest way to check the limits is to shift to RD high (or FD to low) then ignore the lever, and tug the bare cable away from the frame. If the limits are right the cage will move between the freewheel sprockets or chainrings but not overshoot at either end.

You would be able to see the cage move if it was in contact with either limit screw, either high or low, and you tightened that particular screw.

General comment:

If you don't know how the derailleur works or is adjusted, the chances of you correctly fixing it are very low. Read the instruction manual for that model derailleur (available online by model number), get some help from a more experienced buddy or take it to a shop. Basic front derailleurs have 5 parameters necessary to function correctly, and newer Shimano derailleurs have more like 9.

My thing is that I enjoy the challenge of repairing the bike myself. Plus, I have three kids and can't afford to pay for repairing 5 bikes every couple of months. Or even paying for one.

The other posts have proven very valuable.

Keep 'fidgeting', I'm sure you're doing it correctly...

Three kids, at least one of them on a bike with a front derailleur---learning to do the adjustments is a very good idea. Especially if any of them are at an age where fooling around with bike adjustments (when you're not looking) seems like fun.

There are tons of YouTube vids on how to do just about anything on your bike so they can be very helpful. "Park Tools" do some very good how-to vids as well as some that show you how a component works. "RJ the Bike Guy" is another good source for vids and usually works on used parts with a little dirt on them just like us home mechanics will do and offers ways of making some of your own tools if you don't want to spend a bunch of money on special bike tools. Plenty of other vids from other sources but these two I can vouch for.

When advising newbies in learning how to maintain/understand their bikes, besides suggesting what others above here have mentioned, I often suggest that one finds a "curb lawn" bike to do the initial efforts on. If one screws things up it won't mater. The basic principles of der function are the same across the price range for the most part. So to for brakes, spokes wheels and more. The learner bike won't care if one takes weeks to do a job on it. It won't care if all one does is to look at it for 5 minutes while the dinner pasta water is heating up. When the time comes to work on bikes that are in use the repairs will go faster and often be less frustrating.

Many ft ders (and rears) are constructed so one can view the parallelogram link tabs that contact the limit screw ends. If the cable is exposed one doesn't even have to pull a lever to move the cage in and out. If the ends of the limit screws are hidden (and some are) one can hold the cage at it's outer most travel point and at the same time turn one of the limit screws to feel if that's the one controlling the outward travel. By keeping that cable taut one can often feel the change in cable tension or pull with the screw moving the tab. Andy

Thank you all for your very helpful suggestions! What I find most amazing about the bicycle is how much of an art the repair process is.

Robots won't be replacing bicycle maintenance anytime soon.

Post of the day. Never thought of that!

Yeah, it is striking to me how non standardized the bicycle is. The range of spoke sizes alone is astonishing. And the process of tensioning the spokes can't be routinized the way you can lug nuts on a car wheel.

​​​​​​I got the front derailleur mostly right by realigning the front derailleur cage and then playing around with the limit screws. Thanks again!

How is advising you to read a manual instead of blundering around in the dark have no value?

Probably the way the message was delivered had some negative effect.

I suppose politely encouraging people to screw up their bikes by continuing to guess is always the most comforting thing to hear.

People don't start screwing with limit screws for no reason. The OP has a derailleur that isn't shifting correctly, and explaining only a single part of derailleurs work is a disservice.

DON'T "make" the bracket move by turning screws. The metal in the DER body is very soft vs the STEEL screw threads.
"Pull" the DER off the stop to relieve tension/force and then turn the screw.
The screw heads are a JIS Phillips. Not our "usual" Phillips. That's why the screw heads are getting screwed.

Although it's relatively safe to adjust the FD-L screw while the shifter+chain is on the smallest ring, since the cable is slacked, attempts to adjust the FD-H screw while the shifter+chain on the largest ring, as the cable is taut, can strip out the threads of that screw, as well as bend the FD.

​​​​​​It is very valuable information. thank you for the tip!

Here is a critical skill for any bike mechanic to develop: look closely at the part you are working on. In this example, you would be able to see the "working end" of the limit screws and see where they contact the derailleur ONLY at the "limits" of travel. From that, you would be able to understand what their purpose is and how they work and how adjusting them when they are not touching anything would not have any effect. As Yogi Berra so wisely stated: You can observe a lot by watching.

At that point you might also note that the stops have little to do with shifting itself, and are rarely involved in fixing poor shifting performance.

I really like doing my own maintenance. The Park Tool guides are the first thing I look at. They start from the beginning,showing each step, no prior knowledge needed.

When derailleurs are out of adjustment and a slight turn in the correct direction of a barrel adjuster doesn't fix it, I like to start from scratch using the Park Tool guide. This involves checking derailleur cage parallel, the clearances to the cog/chainring, adjusting the limit screws, then finally adjusting the shifting itself.

Limit screws: these screws usually hit a spot to bottom out on the derailleur, which limits movement in that one direction. For some reason, they don't often get marked H and L. Shift to the biggest cog, then look at the screw end, not the tool socket end. One screw will be very near part of the derailleur body, the other will have a big gap, since it's for the other limit.

~~~
Tool guides show the correct steps to make an adjustment.

For example, adjusting a stem is quite simple, once you know the process. But it's just not obvious at first, by a visual inspection. The cap is only for setting the bearing preload, not at all for tightening down a loose headset. Follow the correct steps, and it's simple and accurate.

"For example, adjusting a stem is quite simple, once you know the process. But it's just not obvious at first, by a visual inspection. The cap is only for setting the bearing preload, not at all for tightening down a loose headset. Follow the correct steps, and it's simple and accurate." rm -rf

And this would be especially hard to discern if one had a quill stem:) Andy

I'm not a professional mechanic and don't claim to be an expert, but based on my own experience as a home mechanic, I usually recommend that until adjusting a front derailleur becomes second nature, always use either a good online guide (Park is almost always good) or the derailleur installation/adjustment instructions.

Start at STEP ONE and proceed step by step. Don't skip anything. Even if STEP ONE requires you to remove the cable and derailleur and re install from the beginning. This will almost always work well for a beginner and won't get you balled up figuring out what's going wrong among the various adjustments that are made (derailleur height, alignment, cable tension, limit screws, etc.)