Front mech for the tandem

[phil653]

I need a new front mech for our newly refurb'd tandem. It was still wearing its original Simplex pushrod front changer, a relic from the shed of the previous owner and still working well after all these years until we had a prang on a test ride. The chain snagged, still not sure how, and has comprehensively borked the pushrod and cage. The cage could probably be mangled back into some semblance of shape but the pushrod is beyond redemption, and thus the mech is knacked.

So, we need a new'un. The chainset is a same side drive, so a triple of which the two outer rings carry the drive chain, currently 52-36, so a 16 tooth difference. At the back it's an 11-34 9sp cassette and another relic, a vintage Shimano Crane long-cage. Both are controlled by bar-end friction shifters.

Going over the wiggle/chain reaction/sjscycles catalogue pages I'm a bit befuddled by the choices.  Cable routing demands a mech that receives the cable from above, MTB style, but specs for mechs like that seems to be for much smaller rings, as MTBs tend to have.  Can the panel steer me towards a suitable model, preferably not too spendy?  Ta muchly.

[LittleWheelsandBig]

There are a couple of obsolete top pull road mechs but the chances of finding them are low. There are bolt-on pulleys that convert road mechs to top pull. That might be your easiest option, provided the road mech can cope with the chainline.

[Torslanda]

I would support the pulley approach, along with a 28.6 braze-on adapter then your mech of choice. Unless you can find a band on mech the correct size. Spacers are OK but inevitably a compromise. Personally, I'd go for a Sora3400 double or Tiagra up to 4600 but any road double would cope nicely.

[phil653]

Something like this?

https://www.sjscycles.co.uk/gear-spares/jtek-mech-verter-318-mm-black/

[Torslanda]

There's a 28.6mm version which I'm assuming is the size you need as I've never seen a Simplex mech for a bigger seat tube.

Don't take my word for it though. Measure twice, order once.

[phil653]

Had I taken a little more care I would have noticed the smaller size, and you are right, the seat-tube measures up at 29mm on my vernier so 0.4mm is within tolerances for fitting the parts, both the Jtek "Verter" and a road double mech.

Thanks to both for the steer on this. Rosie will be back on the road after a very long lay-off just as soon as I can get those new bits. It's been a long time coming. I'll try to remember to post some pics.

[mzjo]

Why does the front changer need to be top pull? Surely the original shouldn't have been if it was correctly mounted? I can't think of ever having seen a top pull Simplex. What's the tandem?

[phil653]

This is probably best explained with a photo - better than 1000 words and all that.  See below.

The tandem dates from around 1970 or possibly earlier as it has Bayliss Wiley bottom brackets and they went out of business in 1969.  The original cable routing, or at least the routing it had when it came into my parents hands in 1984 had the levers on the captain's top-tube. The cable route then ran along the stoker's dropped top tube and where it meets the stoker's seat tube the front mech cable runs down through the body of the Simplex mech to an underslung lever. Cable pull then pivots the lever to advance the pushrod and move the cage outwards for the big ring. During the rebuild I (well, a compliant metal worker, actually) added the extra cross brace on the frame from the stoker's seat cluster to the dropped top tube to prevent the tail-wags-dog effect that had caused some frame cracking. But I saw no reason to replace components that were still working fine. All the front mech needed was a good lube and new cable - until I ruined it all with the chain snag incident. I've never considered if it was correctly or wrongly mounted. It worked fine and if it ain't broke.... But then I did exactly that. The irony is that the one part that usually fails on these, the 'Delrin' plastic mounting collar is just fine, but the pushrod mechanism isn't. So anyway, the cable routing is what it always was, top fed, top pull. Hence my need to replace like with like.



Sorry about the focus. Nice sharp wall, not sharp frame.

[mzjo]

Sorry the photos are absent. I should have a Simplex pushrod changer in the bits boxes, I certainly have a parallelogram one. I will look. Why can't you use a top pull mtb changer? I have a much older tandem with a similar transmission set-up as yours and I use a mtb changer, although bottom pull in my case (and very basic but it does have a cable stop built in which solves the cable run problems).

Ladyback tandems (which I assume yours is) are generally notoriously flexible, particularly at the back.

[markfh]

You might want to have a look at the Shimano CX70 front derailleur.  It is a 10 speed rather than the 9 speed you are currently using on the rear cassette but it appears to be available in top pull and designed for a 50 tooth outer ring and a 16 tooth difference between front chainrings.  One thing you will need to check is whether it can achieve the chain line you are using bearing in mind that you appear to be using the outer two rings of a triple as a double which will a wider chain line than would be normal for a double.  If this is an issue then one option is to use a derailleur designed for a wider diameter seat tube with an eccentric shim.

[phil653]

Can anyone else see the photos?

If not, here's a second go at posting them. Firstly Rosie, the former ladyback tandem



And second a frankly poor photo of the front mech and cable routing

[Brucey]

I would suggest that you consider rerouting the gear cable, and then using a standard bottom pull mech.

For example you could run full housing along the front down tube and along the drainpipe. A shouldered ferrule can allow the housing to run into the extant cable guide fitting, repositioned at the base of the rear seat tube.

This would allow the use of one of dozens of bottom pull mechs.

If you want a top pull mech there is (was, you'll have to buy one used) a LX model FD-M561 which was available in top pull. Other mechs which are top pull, bottom swing include some 'hone', SLX, XTR models.

cheers

[phil653]

Thanks to one and all for the useful advice.  In the end I think I'd rather stick with the existing cable routing as it's all set up already and shares guides with the cable to the rear mech. Just ordered a Tiagra 4600 front mech as it was on offer at 33% off so cheaper than the Sora, plus a Jtek 'verter'.  Once fitted and fettled I'll let you know how it works out when Rosie Rides Again, the sequel.

[mzjo]

I think the photo problem was internet related - there were some photos in other posts that didn't show as well and now I have yours both times.

This tandem looks curiously french to me - Gitane, Peugeot or Motobécane (in UK import version). I have seen pictures of a Gitane that was very similar. British builders would have probably braced the frame rather more solidly.

Have some nice rides!

[Torslanda]

What did I fall over today? A traditional Shimano front mech with a top pull. Nice wide cage too...

[Brucey]

What did I fall over today? A traditional Shimano front mech with a top pull. Nice wide cage too...

I did the same thing and thought of this too!

cheers