Front derailleur not having enough travel

Question

I've got a bike running 9 gears in the back 3 in the front. This is the first bike I've been working on so it has some history. Also, I made plenty of mistakes while learning how to take care of a bike.

The bike is running a Shimano Deore LX as front derailleur over a firex crankset. Over time I disassembled the bike as a whole and put it back together. Also, the bottom bracket was replaced.

Now, the problem: When I first started fixing my bike I removed the gear switcher and replaced the bottom bracket. When I installed everything again I had trouble adjusting the front derailleur. Back then I thought I was doing something wrong and gave up on a perfect adjustment. However, coming back to this bike many years later I can't get it right either.

The problem is that the derailleur is not having enough travel to comfortable reach the outer sprocket. I've unscrewed the H screw completely. The only way to kind of run the bike is to put crazy pressure on the gear cable but that has led to a broken cable every year.

The only reasons I can think of for not reaching the outer sprocket are two things:

First, the chain line could have gotten bigger. Maybe the bottom bracket replacement has made the chain line bigger and hence the derailleur can't reach it. However, I've no clue how that should have happened. I still have the old one and it's as wide as the current one.

Second, maybe the derailleur has failed somehow. I've inspected it but it seems to work as normal. Maybe I'm missing something.

I'm out of ideas. What could I try next?

P.S. I know the gears are bad but I don't want to put money in new ones until this problem is fixed.

Answer 1

Here are some things to check, particularly if this crank and FD once were working well together:

• The FD clamp angle can't be tweaked slightly to give the clearance needed.
• The BB is assembled right, namely there are no extraneous bits between the drive side bearing seal and the cranks. It's possible to imagine the old BB seal or a spacer remaining stuck to the crank when it was replaced, and then the crank gets pushed out more than it should. (GXP bottom brackets would also tend to show signs of excess preload if something like this happened).
• The FD cage isn't bent or distorted in a way that's creating the problem.
• The large ring hasn't been replaced with something weird, or flipped the wrong direction.

You should measure the actual chainline on the crank. The middle ring should be 51mm. This is from the 2010 Truvativ/SRAM crank technical manual:

That may help determine what's going wrong. If the crank has got the original or like-for-like replacement rings and the chainline is out further than that, something is probably assembled wrong. If you measure and find the chainline is on target, then it's probably something going wrong with the front derailleur or its adjustment.

The nominal chainline compatibility for your FD is probably 50 (look it up to be sure), but mixing Shimano FDs with SRAM/Truvativ cranks was common in this era so I doubt that 1mm disparity is causing the problem per se. However, it might create a situation where the margin for error is tiny in how the FD is set up. Your FD is probably one of these LX models (find the stamping to check):

Remember that GXP BBs work by the NDS bearing inner race getting pinched between the step on the spindle and the NDS crank. The step causes a hard stop that you can feel when putting the spindle through. Where it can get confusing sometimes is what's supposed to be present between the DS crank and the DS bearing cover. For some GXP cranks that answer is nothing, in some cases it's a wavy washer, and I believe some have an elastomer (not 100% sure). I believe your cranks are supposed to have nothing there - the spindle is allowed to "float" through the inner race of the DS bearing, and there's a gap between the DS bearing seal and the crank arm. If the chainline is landing at some number greater than 51mm, that would be the first place to investigate. You appear to have no spacers between the BB and the shell, which is correct for a 73mm shell.

Sometimes people see the gap between the DS bearing seal and the crank on GXP cranks that are supposed to be set up that, and put a spacer in there. If so, that could cause the chainline to be pushed out. It will also cause excess bearing preload. I can't tell for sure but I'm a little leary that this is such a spacer:

If the chainline is 51 and you just can't make it work with the LX FD, it's not terribly expensive to just get something like an X5 or X7 from the era. They work with Shimano 3x mountain shifters.

Answer 2

It looks like the problem is that the derailleur clamp has slipped a few degrees around the seat tube, so that it's now pointing a little bit towards the tyre. Note that the position is about right at the front of the cage, but not at its rear, i.e. the derailleur itself is doing the right thing, and the chainrings are in the right place too, but the derailleur is not sitting at a straight angle.

The consequences should be obvious, and so it the way to fix it.

Not completely sure about this, the perspective could trick me and if the chain is in the smallest sprocket it also leads to such an angle, but it still seems a likely explanation.

Answer 3

First thought: do you have enough tension in the shifter cable when it's in the small ring?

Second thought: in your pictures, the outside of the derailleur cage seems to have plenty of chain clearance at the leading edge. Is this only because you're tugging the derailleur into position? If it's holding that position on its own, you may need to adjust its height and/or rotation on the seat tube—it looks as if it's rotated clockwise a bit.

Third thought: I wonder if there's wear in the shifter mechanism so that it's not taking up as much cable as it should.

Answer 4

The problem is that the derailleur is not having enough travel to comfortable reach the outer sprocket. I've unscrewed the H screw completely. The only way to kind of run the bike is to put crazy pressure on the gear cable but that has led to a broken cable every year.

I also have an issue with a lot of cable tension, which in my case may be because I converted from 1x7 gears to 2x9, so I'm not sure about the proper chain line width. I did check that the crankset is tightly screwed on the axle.

In my case, there are two things that limit travel of my 2x9 Shimano SORA derailleur before the unscrewed H-screw could:

1. One of the ends of the torsion spring.

2. A stop: a protruding piece on the mounting bracket that limits the piece that's pulled by the cable.

I know this isn't much of an answer, and this may or may not reduce your cable tension. I found, in my particular case, no other solution than grinding off a bit from both the spring and from the stop to at least allow it to shift far enough over the largest chain blade. I can now use it to shift down when required, but I require both hands to shift back.

edit: I have a chainline of aprox. 48mm, while with the Shimano SORA it should be 43.5mm. After riding the bike and reading Parktool's Chainline Concepts article, I decided against changing the bottom bracket to get a shorter square spindle (should be 110mm in stead of 117), but rather ordered a Shimano Altus 2x9 top-swing derailleur, which should work fine with 48mm chainline. This is because my shifting is great with the current relative sprocket alignment. The only issue is the front derailleur cable tension.

Answer 5

The position of both limit screws looks a bit odd and off