Dominover

I have a hybrid bike with Shimano Gears and am referring to the front derailleur, and specifically the left limit screw.

I've seen this question/issue dotted around the internet so I wanted to run this by the experts.
My Front Left Derailleur limit screw connects to nothing at all. I can't upload pictures yet.
I've just realized that this is probably because, at least on this bike, the left limit screw is not needed. The Derailleur is clamped so close to the vertical seat post tube that the internal mechanism of the derailleur which would normally allow left or right movement to set the left stop limit, is already limited by the vertical seat post tube. It looks to me like the Derailleur has been fitted this way to forcibly guarantee the correct spacing between the left derailleur guide and the chain (around 1mm or so).

The right limit screw allows for left and right movement of the Derailleur chain guide, but for the reasons explained above, the left limit screw does nothing. Even when screwed right in, it barely touches the mechanism inside the Derailleur.
Are my assumptions about this correct. Does the way this derailleur has been mounted automatically set the left derailleur guide limit in turn doing away with the need for the left limit screw?
Also, is this common practice to build bikes this way?
If you want pics, I'll have to DM them to you. This forum doesn't allow me to upload photos because I haven't made ten posts yet.

Thanks.

tFUnK

I don't think it's common but it happens. I noticed it on two of my road bikes when I switched from standard 53/39 to compact 50/34 cranksets and had to lower the FD a tad.

Dominover

It seems to be by design. Not the Deralleur but the way they have used the bike frame to enforce the left stop.
The bike came this way and nothing has been changed on it.

Country too many videos on this topic the cable feeds into the derailleur from the top so the spring mechanism is not under spring tension when the chain is on the smallest cog furthest to the left (at the front).

SurferRosa

In discussing derailleur limit screws, it's much better to use terms high/low or inner/outer than left/right.

Kontact

It isn't by design. The derailleur is being stopped by something else - like the seat tube or cable tension. It is an example of poor frame design or incorrect part specification. Or something is bent/broken.

FBinNY 

The combination of a fat seat tube and inboard crank position can create a situation where the FD fully bottoms out against itself in low. Note, either alone can cause the same issue.

In extreme conditions, it might be bad enough that good low gear trim, and or downshifting is problematic.

The fix is to move the crank out 2mm or so, if possible. Or buy a more recent FD, designed after fat seat tubes were SOP.

Iride01 

That low limit screw is sort of a last resort. So is the high limit. In a perfect world, they don't need to be touching anything. They just help prevent over shifts that might drop the chain. And typically the limits are set without the cable installed on a new installation. And if they are aligned correctly don't need to be reset ever again so long as nothing else changes on the bike.

dedhed

Does it shift fine? If so don't' worry about it.

grumpus

It sounds like the wrong axle has been fitted, the crank has stretched, or you have a double derailleur with a triple crank. The adjusting screw should work.

wheelreason

Yes.

Kontact

I have two 90s Shimano derailleurs that hit the 35mm seat tube on my 94 Basso before it fully clears the small ring. Some stuff just wasnt universal.

KerryIrons

Please explain the mechanism of "crank stretching."

Kontact

Probably referring to the square taper hole expanding from overtightening, causing the chainline to shift left.

grumpus

Indeed - you could probably make those work together by using a different axle or crank ... people want narrow Q factors but they want triple chainsets and they get grumpy when their heels clip the chainstays and why are there so many widths of hub and cassette? It's a never ending story of compromise and innovation and new standards and non-standard ...

Kontact

I just switched to a different front derailleur. Easy.

Dominover

In the end I figured this out. Thanks for all the replies and help.
All the instructional videos show the right derailleur stop on the far right. On my bike, it's on the far left.
That's why the limit screws seemed to do nothing. I had them the wrong way around. I'm happy to say that I'm riding around now and the bike is going very well.

Dominover

Thanks for all the replies. I eventually worked things out. My right limit screw is the one closest to the frame. On all the instructional videos it's the opposite. The bike is going very well so I appreciate all the input. I'm only learning about bikes all over again because the last time I owned one things weren't as complicated.

Jeff Neese

As was mentioned above, they are called high and low limit screws, not left and right.