Rebuild -Front derailleur advice needed

[fredN4]

cable it up and see how it works. looks similar to the campag comp triple on my Look, which works fine, and with a 26 small ring.

[Brucey]

I'm pretty sure seat tube angle wouldn't make a difference - just thinking if you rotate it with the bb as the centre, the distance from the chainring is the same, but the seat tube angle changes ....... If that makes sense.

yes I agree, variations in seat tube angle shouldn't cause the tail to be high. Tail high does reduce the capacity of the mech though; the chain is more likely to tangle with the bottom of the cage when on the small-small combinations.

Always makes me wonder how those oval chainring set-ups work with double clangers?

'badly' I think.....

cheers

[BigG]

The only part of the outer plate of a front mech that does anything useful when changing down from the big ring is the section adjacent to the main mechanism. It only has to derail the chain at that point which (in my experience) is a simple task that requires no particular accuracy of shape or position. There is always a big gap between the tail of the mech and the middle ring which is only marginally affected by the fit of the outer plate to the big ring. The change down from the middle ring does not in practice seem to be any more difficult than from the big to middle ring. The plate that does all the hard work is the inside one which has to lift the chain onto both the big and the middle rings. It is the fit of this plate that matters, not the outer plate. It must be a fairly good match of the middle chainring with indexed mechs as the traditional overshoot and readjust technique which always made friction mechs work is not available.

[Brucey]

The only part of the outer plate of a front mech that does anything useful when changing down from the big ring is the section adjacent to the main mechanism....

I'd add the caveat 'usually' to that. Under some conditions (eg on bumpy roads) the chain can remain partially derailed and partially stay on the chainring, and can jam beneath the outer plate of a badly fitting/shaped front mech.

That, I think, is why good FDs are shaped with long tails that hug the periphery of the big ring; you can't have a big gap everywhere (else the chain will regularly overshift off the big ring into the crank) so you have to have a small gap somewhere. If that gap is tapered from 'large enough to clear a derailed chain' to 'not' then sooner or later the chain will find a way to jam in that gap.

You might be careful and/or ride on smooth roads so that it is an event that happens once in a blue moon, but IME FDs are more reliable if the outer cage plate hugs the big ring fairly well. Most manufacturers take a good deal of effort in making sure that this is the case, and it is not pointless activity...

BTW there is whole separate issue concerning the shape of the inner plate, but aside from ridges etc possibly being in the wrong place and/or the capacity of the mech being altered, a tail-high FD isn't definitely going to be a disaster in this respect.

cheers

[fausto99]

Do you have any photos of how it used to look?

Sorry, no.

This is what I achieved after repeatedly loosening the clamp and re-tightening while leaning on the back end of the cage.



I think the new paint/varnish was not allowing the two halves of the clamp to settle into full alignment and, after 21 years use (!), there is some play in the upper front cage to body pivot.

[Mick F]

I've not seen a Campag front mech follow the profile of the big ring like that before.
I'm jealous!

Therefore, it's possible, but has been impossible on both the frames I've used Campag on. That's Campag 980, Victory, Mirage, and latterly Comp combined with a Raleigh Double 52/42, a Stronglight Double 53/38, a Mirage Triple 52/42/30 and now a Chorus Triple 53/42/28. These have been band-on and latterly braze-on with clamp converter.

Why can you get it right, but I couldn't?

[Brucey]

really the adaptor on your moulton needs to be tapered in order that the extra offset of the FD doesn't make it more tail high than normal.

Of nineties and noughties mechs I can't speak much but IIRC much older campag mechs fitted OK.

cheers

[CREPELLO]

I'm pretty sure seat tube angle wouldn't make a difference - just thinking if you rotate it with the bb as the centre, the distance from the chainring is the same, but the seat tube angle changes ....... If that makes sense.

yes I agree, variations in seat tube angle shouldn't cause the tail to be high. Tail high does reduce the capacity of the mech though; the chain is more likely to tangle with the bottom of the cage when on the small-small combinations.

On a related theme, Shimano have marketed their MTB front mech's for trekking bikes as well MTB's. One type is marked "for chainstay angle 63-66 degrees", the other type is marked "for chainstay angles 66-69 degrees". What's that all about? I've never had an issue with using the standard MTB mech on a touring/trekking bike (up to 48T outer ring). IIRC, my old Galaxy came fitted with the trekking type mech. Replaced with a standard mech with no shifting issues at all.

[Norman H]

As chainstay angle decreases there is an increasing risk that the tail end of the cage will conflict with the chainstay. Especially if you are using a smallish outer ring and need to lower the mech to achieve proper clearance. Hence Shimano offer the two options to suit.

[Mick F]

really the adaptor on your moulton needs to be tapered in order that the extra offset of the FD doesn't make it more tail high than normal.

Funny you should mention this, but this afternoon I spent a happy hour with a file and modified the adaptor to give a degree or two of a "droop". The front mech is better positioned now. Maybe I could have got a bit more if I'd spent more time, but I think it'll do.

Meanwhile, the Campag mechs I listed above, aren't as good as I've achieved now with the Moulton.

[fausto99]

Why can you get it right, but I couldn't?

pass

p.s. glad to see you sorted it on your Moulton rear forks. Here's one I did earlier (sold now) to finance my Pinarello .

[Mick F]

Very nice indeed!

What gearing was on that?
Looks like the outer chainwheel isn't a big as mine, so it must be that you had a very small cog on the cassette. The rear mech doesn't look very long, so you must have had a narrow range?

[fausto99]

What gearing was on that?
Looks like the outer chainwheel isn't a big as mine, so it must be that you had a very small cog on the cassette. The rear mech doesn't look very long, so you must have had a narrow range?

Now you're asking. I sold it about 4 years ago. I don't remember all the details. The rear cassette was a std Shimano 11- something, 32 maybe. I have a photo:



So 17" wheel x 53/11= 82 inches. Big enough for my little legs .

[gxaustin]

My big crank wheel is 46t so all my front mechs fit very approximately at the rear and the rear of the mech only just misses the chain stay. The derailer works fine. I'm not aware that one can get a front derailer to fit a 46t (cyclocross) chainwheel. Certainly the Ultegra 6800 group set I bought with a 46/36 chainwheel has an identical front derailer to a Tiagra 4700 derailer from a 50/34 compact. Both of the above have shorter 'tails' than the one shown on the photo above and therefore clear the chainstay comfortably.