9-speed triple front mech for outer 48t chainring?

[toontra]

I'm looking for a front mech that will fit a Clockwork MTB, so clamp-on 28.6 tube (shims available that's not an issue), top pull and top swing (so low clamp).

It's to work on a 9-speed set-up with a triple chainset with an outer ring of 48t (this seems to be the main limiting factor).

A lot of ones that seem to fit the bill are now obsolete. Any suggestions as to where to look?

PS I'd really like new (even if old stock) rather than used.

[Brucey]

NOS front mechs appear on e-bay quite often. However there are a couple of things you should bear in mind;

1) the chainstay angle that your FD is meant for; shimano often made two models, one with a large chainstay angle (for 26" wheels) and one with a small chainstay angle (for bikes with 700C wheels). However the mechs for 48T chainrings (in 9s or higher) tend to be the latter sort not the former, and it is the former you want, isn't it?

2) the FD is usually specific to the middle to big chainring interval, 10T and 12T models are most common, and the wrong one won't work as well as the correct one.

cheers

[toontra]

Thanks Brucey. Yes, lots on ebay - almost too many, and so many variations that it's difficult to establish if they're suitable, particularly as the descriptions are usually quite vague.

It's for an early 90's MTB steel (Orange Clockwork) frame with narrow tubes (28.6 seat-tube). As you say, many of the mechs that fit all the other requirements say the max outer ring is 40, 42 or usually 44. The difference between outer and middle shouldn't be an issue as I run 48-38-28 (typical touring, or at least once was!).

[Brucey]

... The difference between outer and middle shouldn't be an issue as I run 48-38-28 (typical touring, or at least once was!).

that means that the mechs which are meant for 12T m-b interval won't work very well; if you want them to work reasonably well then they will have to be set 4mm higher than normal and this may encourage the chain to overshift off the big ring more than it should.

I would suppose that you will more easily find a bottom pull, bottom swing mech; you can convert the pull direction using a pulley device, and using a high band usually means little more than losing the seat tube bottle bosses. Very occasionally the lower boss is in the right (wrong) place such that it prevents a mech from being fitted at the correct height. FWIW top swing mechs from that period were often poor, lacking in biasing springs etc which meant that they often rattled themselves to death when using the middle and big rings.

A 7s FD will work and prior to Microdrive stuff becoming popular they were all designed to use a 46T big ring so 48T usually works OK too. However the low band, top swing, top pull type is the least easy to find. Top pull mechs at that time tended to be bottom swing types.

cheers

[Nigel]

I'd just add one more detail; if you find a mech with the right "angles" for the seat tube, but it may have the wrong off-set (chain-line) for the rings.
I had that situation on one of our bikes (a 1990's small steel MTB frame). Solved by making an eccentric spacer, rather than a simple cylindrical spacer. That gave me about +/- 5mm of movement on chain-line for the derailleur mechanism.

Spacer was made from delrin, and I have a lathe which can do such work. Aluminium is another option for material.


- Nigel

[toontra]

Thanks both. This is even more complicated that I thought originally! I was naively hoping someone would give me a model number of something that would suit

I remember being told a few years ago that a Deore FD M590 or SLX FD M660 would work (if top/dual pull). Any idea if either of those fit the bill (if I can track them down)?

[mikeymo]

Will an M531 do?

https://www.ebay.co.uk/itm/Shimano-Deore-M531-Triple-Front-Derailleur-3-x-9-Clamp-34-9mm-eb5-/164478238587?hash=item264baabf7b

I can vouch for the seller. In fact if you get that one it's probably one I returned, once I realised it was a 50mm chainline. And yes, it looked brand new but not in retail packaging.

[Nigel]

Its possible the one on our bike is the Deore FD M590; can;t be 100% certain as I've not dug out the instruction sheet for it, but looks like the online pictures.

Our setup is a 3x7, but the mech is labelled as a 9-speed on its top face sticker. Used with a 24-36-48 triple, with eccentric spacer moving mech inwards by a few millimetres. Its on a very small bike with a very light rider who doesn't hammer anything: the outer ring is rarely used.
Shifters are STX combined flat-bar brake/gear trigger units. Setup was tricky, chain rattles on edges at extremes of middle range, but not sufficient for an issue with the rider. Once it was set, its stayed working with only routine cleaning/maintenance.


- Nigel

[bgnukem]

... The difference between outer and middle shouldn't be an issue as I run 48-38-28 (typical touring, or at least once was!).

that means that the mechs which are meant for 12T m-b interval won't work very well; if you want them to work reasonably well then they will have to be set 4mm higher than normal and this may encourage the chain to overshift off the big ring more than it should.
.......
cheers

Second this. I tried to use a mech designed for a 12T difference with a 10T large-to-middle 'ring gap and it performed appallingly until I reduced the middle 'ring size by 2T.

Also can be hard finding a 28.6mm diameter clamp these days due to larger tube diameters, but if the clamp is too large you might find you can't shift onto the small 'ring as the mech starts out being spaced too far outboard from the seat tube. An eccentric shim/spacer can be used as stated upthread but a normal spacer won't help - also had this problem on the same bike when I replaced the chainset and ended up with a chainline closer to the frame. I replaced the 34.9mm-diameter clamp front mech with a 28.6 and sorted the problem.

[toontra]

Thanks for the further info.

After much dredging of the net I have found the following which seems to tick all boxes - Alivio FD-T4000-TS6

Correct chainstay angle 66-69 (26' retro MTB)
9 speed triple
48 max tooth

The only issue might be using a shim to reduce the clamp from 34.9 to 28.6 (as bgnukem points out). Hopefully I can solve that by using the spacers included in the outboard bottom bracket (Hollowtech MT800) if it's a problem.

Only available new from a China ebayer!

[nsew]

The Shimano FD-CX70 ticks a lot of your boxes and is known to shift awkward triple set ups. I had no interference with bottle cage bosses however that was a bottom pull.

https://bike.shimano.com/en-EU/product/ ... 0-F-T.html

[Brucey]

Thanks for the further info.

After much dredging of the net I have found the following which seems to tick all boxes - Alivio FD-T4000-TS6

Correct chainstay angle 66-69 (26' retro MTB)
9 speed triple
48 max tooth

Alivio FD-T4000 is meant for 12T chainring interval, not 10T

cheers

[toontra]

Alivio FD-T4000 is meant for 12T chainring interval, not 10T

Do you think that is likely to be an issue in practice? If so, would running a 48-36-26 work?

This is all so weird. It's not that long ago that 48-38-28 triple was a bog-standard touring setup. The components now seem rarer than hen's teeth.

[Brucey]

I'd suck it and see, if that is the best match you can find.

cheers

[slowster]

The Shimano FD-CX70 ticks a lot of your boxes and is known to shift awkward triple set ups. I had no interference with bottle cage bosses however that was a bottom pull.

From https://www.renehersecycles.com/trouble-with-sti-triples/:

Addition (3/7/2015): A reader pointed out that the “top pull” version of the CX-70 derailleur does not swing far enough to shift a triple crank. Only the standard “bottom pull” version works for triples.