Front derailleur woes

[peetee]

Judging by the photos that bracket axle can only be approx 5mm shorter on the right hand side before the small ring gets too close to the frame tube. I think you are still going to be pushing the limits of the mech so perhaps a combination of a carefully selected crank length and an eccentric shim for the mech will be enough to get you there.

[belgiangoth]

I can shift across the FD using a MTB shifter (I think - the pair with the other shifter I was talking about). Just a bit tricky to get into top gear.

[gxaustin]

so perhaps a combination of a carefully selected crank length and an eccentric shim for the mech will be enough to get you there.

I like the idea of an eccentric shim. How does one procure such a thing?

[Brucey]

so perhaps a combination of a carefully selected crank length and an eccentric shim for the mech will be enough to get you there.

I like the idea of an eccentric shim. How does one procure such a thing?

e.g.
https://www.sjscycles.co.uk/gear-spares/thorn-eccentric-front-mech-shim-286-to-349-black-plastic-hand-finished-split/

cheers

[gxaustin]

That's interesting thanks. I don't think it will help me because I have a braise on bracket - but I shall bear it in mind. A friend told me he'd been running with a gap of about 10mm between the lower edge of the derailer and the chain wheel (44t in his case) with no problems at all. Accordingly I just stopped worrying and got on with riding my bike. I've ridden over 1,500 miles on it so far with no issues and no chain shipping.

[belgiangoth]

Can I check a few points:
1 - Shimano and SRAM Front Mechs work interchangably.
2 - Shimano Road and MTB Front Mechs are different
3 - This is not an issue with Twist shifters (or, of course non-index shifters)
4 - With cable removed the mech should sit over the bottom gear, if it doesn't this is a problem (check BB or look at the Jtek solution)
5 - New crank/gearset should swap straight in unless...

I think point 2 will explain my issue with the trigger shifter - I can get accross and into all gears, but it's a pain. I am reconsidering returning to twist shifters, might see if I can sort them out as they are rather sticky.

[Brucey]

Some of the things in your list are true some of the time. It is difficult to advise you very well because you have not revealed the model numbers on any of the parts you are trying to use.

I can tell you that the FD in your pictures looks like a shimano 'road triple' FD and that this FD type normally requires a lot less cable pull than an MTB FD.

However the shift ratio gets smaller and smaller as the FD reaches out further and further and by the time it is as far out as it can be then you can pull as much cable as you like, the FD won't move any further. You may well have this exact trouble because your chainline is wrong. You change shifters all you like and it won't fix that problem.

I suggest that you

a) identify the model numbers of the parts you are trying to use

b) measure the chainline (it isn't difficult) and compare it with the specs for that mech

c) get the correct length BB so that the chainline is correct for that FD

and see if that works. I can tell you that if you can only get the mech to work with the limit adjustment screws set as they are in your pictures, you are definitely on a hiding to nothing with most forms of indexed front shifting. It might work OK with a thumbshifter though, because that isn't indexed.

cheers

[peetee]

Is that a chain guard it the upper part of the photo? It looks rather narrow. Perhaps this bike started out with a double crankset and the previous owner swapped to a triple and it just didn't work. The swap may have included the bottom bracket but the wrong length was chosen. Shimano triples (for example) can be fitted to 113mm or 123mm axles depending on the bike.

[belgiangoth]

Hi Brucey,

where will I find this information on the Mech/Derailleur? Mech is tiagra triple, dérailleur is Deore Mega 9. Can't see anything else indicated on them.

peetee, I thought that the previous owner might have done that, but speedmachines (despite the name) are more of a tourer. Still I think BB could well be the issue.

[Brucey]

....where will I find this information on the Mech/Derailleur? Mech is tiagra triple, dérailleur is Deore Mega 9. Can't see anything else indicated on them...

markings are on the rear of each derailleur. But in fact that they are tiagra triple and deore 9s is enough to pin them down; all shimano 9s RDs (MTB or road) use the same shift ratio and all tiagra triple FDs use a 'road' cable pull, not an 'MTB' cable pull.

A 'road' shifter will probably run out of cable travel; if you set it to access the big ring then this will take more cable pull than normal (from the middle ring position, which may not be set correctly either) and there will not be enough cable slack left to access the small chainring in all probability. Fixing the chainline should solve that. There is also the possibility that the FD is partially seized (common in Tiagra FDs) or that the cable run is binding; again this is common on recumbent machines; the cable housing is long (for a FD) and fills up with water.

cheers

[belgiangoth]

So ... if a buy a set of 3x9 Tiagra MTB shifters they will work (my other option is different front and rear shifters - which would not be that tricky if I use twist shifters I guess). IIRC you said 3x10 Road would work since road 10 pulls the same as MTB 9?

[Brucey]

So ... if a buy a set of 3x9 Tiagra MTB shifters they will work (my other option is different front and rear shifters - which would not be that tricky if I use twist shifters I guess).

tiagra models include dropped bar shifters and flat bar shifters, which operate the same (road) FDs. To describe them as MTB shifters is misleading. MTB shifters work MTB FDs which are different to tiagra.

IIRC you said 3x10 Road would work since road 10 pulls the same as MTB 9?

no I said the RDs use the same shift ratio (except for 4700 which is different), which is not the same thing at all. You can expect to take a 10s setup and substitute a 9s RD and have it still work or a 9s setup and substitute a 10s rear mech (capacity permitting) and likewise have it still work.

The shifters of course pull different amounts of cable for the RD; 9s pulls ~2.5mm per click and 10s (road) pulls ~2.3mm per click.

cheers

[belgiangoth]

Okay Brucey ... so ...
A tiagra flat bar setup would work.
A road 3x10 speed setup should work.
Twist-shifters will work.

I shall endeavour not to misquote you in the future.

(You did say that Brexit would give more money to the NHS, Donald Trump is a clever guy and Theresa May is a Strong leader, right?)

[Brucey]

....Twist-shifters will work....

for the FD only if they have the right cable pull or are micro-ratchet type. Most indexed twist shifters work MTB FDs not 'road' type.

I shall endeavour not to misquote you in the future.

(You did say that Brexit would give more money to the NHS, Donald Trump is a clever guy and Theresa May is a Strong leader, right?)

errr.....

cheers