Author Topic: Front Derailleur Problems on Explorer  (Read 4570 times)

Ian Shore

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Front Derailleur Problems on Explorer
« on: March 10, 2013, 04:01:51 pm »
Hi,

I am a new to the forum and I am hoping for a little advice concerning my Explorer tandem which I bought second hand late last year. The bike is 10 years old and in good condition having covered around 5000 miles with the previous owner who had it from new. Since I have had it I have replaced cables, brake pads and tyres and given it a basic service and all is well except for one thing! I am unable to correctly adjust the front derailleur and however much I adjust it I have problems changing on to either the large or small chainring. Regardless of whether it is the large or the small chainring it is difficult to change on to it will change on to the middle, but not usually cleanly. I am no expert on gears but have always managed to set them up on my current and previous bikes and have the rear mechanism working perfectly on the Explorer. I have triple-checked my technique but I just seem unable to get the front to change properly-though interestingly it changes properly when in the garage but not out on the road with my wife and I aboard. Roadside meddling does not solve the problem!

The tandem is fitted with Shimano LX changers (which despite cleaning and replacing the cables have a somewhat stiff feel) and a Suntour XC Comp front derailleur and also a Thorn Power Pro 24/36/46T chainset. Searching on the internet the Suntour changer seems to feature on mountain bikes-I am assuming that its use is something to do with it being on a tandem and that this is also the reason why a Shimano LX front changer is not used? Is it possible that the component is simply worn and needs replacing or am I going wrong somewhere? If replacement is advisable could you suggest a suitable (inexpensive) replacement?

Thank you in advance for your help.

Danneaux

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Re: Front Derailleur Problems on Explorer
« Reply #1 on: March 10, 2013, 06:39:21 pm »
Hi Ian!

Welcome to the Thorn Cycling Forum!

I'm sorry to hear you've been having shifting problems with your tandem's front derailleur. Tandems can be a bit "special" when it comes to shifting problems because of the long cable and housing runs that can result in greater friction. Too, the power demands of two people add to whatever problems might be present.

I can think of several contributors to the problem and one indirect solution, all of which solved the shifting problems on my own tandem:

• I suspect the housing may be a problem, even though you mention replacing the cables. I found the real solution for me was to replace both cables and housing to minimize friction. In places where there were open runs (my Burley Rock 'n' Roll tandem routes the cables inside the frame...and used the frame as the housing for much of the distance), sheathing the cables in Teflon-Delrin liners did the trick. Look carefully at the problem...I'm guessing the problem comes not so much when pulling on the shift lever, but on releasing the tension and depending on the derailleur springs for downshifts. That can be a sure sign of excess friction in the system.

• Depending on the front chainline, it is possible the chainset (however many rings there are) is set too far inboard or outboard for the front derailleur to make a clean throw within its limits each way. If you check the SJSC website listings for "Thorn", you'll see they've developed a really clever means to address such problems. There is a spacer that also serves as an eccentric mount to place a front mech with 35mm clamp on a smaller seat tube. This can get things shifting up front while avoiding messing with the chainline.

• After replacing my cables and housings and fitting the liners where there hadn't been any, the final solution that broght great front shifting to my tandem -- even under load -- was the N-gear JumpStop: http://n-gear.com/ It is an overshift catcher that allows one to adjust the front mech past its inner stop; the JumpStop catches what would be an overshift and ensures the chain settles on the small 'ring. Best of all, since it solves the inner/small shift problem, it leaves only the outer/big shift to deal with, taking care of half the problem. The upshift commonly occurs by pulling on the lever with a low-normal front mech, and is much easier to manage than downshifts, especially when dealing with the efforts of two people, as on a tandem.

• As a last thought, it might be wise to check to see if your front mech is "sized" to match the chain you are currently using. If you are using a derailleur meant for, say, 7-speeds and are currently running a 9-sp cassette and chain, the derailleur can fail to make clean shifts...just as you are experiencing. The "gate" is simply too wide to push the chain cleanly onto the next chainring. The SunTour front changer is from earlier days, and may not be a match with your current rear gearing or (more importantly) chain. Worth a look to see.

• If you need to replace the front mech, the standard-issue Shimano Deore front mech is solid and reliable and a good value. I went with  a bottom-pull/top-swing model on my tandem and it works great, all for the princely sum of USD$8 at an REI season's end sale. eBay has them on offer for good prices as well.

Hopefully, something in the above will help. Good luck, and give a shout if these suggestions fail to help.

Best,

Dan.
« Last Edit: March 11, 2013, 04:19:27 am by Danneaux »

Ian Shore

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Re: Front Derailleur Problems on Explorer
« Reply #2 on: March 10, 2013, 07:47:28 pm »
Hi Danneaux,

Thanks for your welcome and your comprehensive reply. As you suggest, I did only replace the cables so I will start with replacing the housings as well-if that does not work I will try your other suggestions.

Many thanks,

Ian