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Triple to Double Crank

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Triple to Double Crank

Old 05-04-13, 07:11 PM
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Trekathlete
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Triple to Double Crank

Thank you for looking at my post first of all.

I have been wanting to replace my 105 triple chainring for sometime and today I did it with a 6500 ultegra chain ring which matches the rest of the bikes ultegra components except for the front derailleur. I've read quite a bit on the forums with people having success story's but they weren't very specific on how they made it work. I am having major problems with getting the derailleur to align properly. I have looked at numerous youtube videos so I feel I am doing the work correctly.

The components are as follows Ultegra 6500 53/39 crank, Ultegra 6500 brake/shifter (it has three position shifts for a triple), and a shimano 105 (triple )front derailleur. I have been told that everything should work fine but I can't get it tuned properly for the life of me. I don't know if its the front derailleur or the shifters up front that is the problem but I think that I'd put my money on the derailleur. I can essentially make the third shift on the shifters non-existent with the limit screws but then when I shift into the large chain ring the derailleur goes way to far over and is actually touching the chain ring with the inside of the derailleur. I used the limit screws and seems alright for the lower chain ring but for the large chain ring they basically don't do a thing. The derailleur seems to be out of limits for the outer chain ring. I can screw it all the way in but then the front derailleur sticks like a fixed position with the large chain ring and it doesn't push the derailleur closer to the bike frame like I would want for a good tune.

I just want to hear if there are any other people who have done it and can give a detailed account. I may be doing something wrong but as far as I can tell everything seems fine and I am fairly mechanical so I should be able to do this if it is possible.

Your comments are very much appreciated.

Thank you!
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Old 05-04-13, 07:59 PM
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You're fighting Shimano's decades of spec specific design. The triple ft der has a cage with a shape for the difference in ring diameters of a triple crank. The placement of the cage's contours were never meant to work with 39/53 ring pair. The shifter cable pull amount is also meant to work with the cable pull needs of a triple ring crank. The cable pull amount needed for the inner to middle ring is not the same as the middle to big ring. Yet here you are trying to make it work with a double and the chainline/placement of it. Now these differences are not large ones but they do compound on each other. Your description of the outer limit screw doing nothing until it does too much and the cage movement jams (at least that's what it seems like you're saying), doesn't ring with my experience. The only way a limit screw can jam a cage movement BOTH WAYS is if the screw has gone too far in and is no longer hitting the cam squarely, instead the screw gets past the edge of the cam and hangs up on it.

I guess I'd change out the ft der first. BUT be aware that if you are able to move the shifter lever enough past the second position (and Shimano had this very problem a few years ago) the shifter can jam and suffer an internal failure. The Ergo levers are completely interchangeable between double and triple ring cable pull needs. Shimano much less so. Andy.
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Old 05-04-13, 09:36 PM
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Andy,

Thanks for the reply. It does seem that I may have a bit of an uphill battle. I read in other forums and people posted that they did it just fine so I assumed the same before I started. But after further investigation today on the forums, I could need a new BB, and front derailleur but I am still hopeful that my shifter will work just fine.

You are correct on your description of the outer limit screw of the front derailleur though. I went and checked and the outer limit screw seems to not do anything at all until you do go to far. It seems wonky but thats how my derailleur seems to work and I looked at the mechanical aspects of it. And my shifter like you said might pull the derailleur to far to make it work well enough for the new double crank I am trying to tune up.

I am getting a little timid on going much further on this project because I have limited funds to work with and was hoping that popping on the crank would be just as easy as that. Now it seems I might need a new BB, Front Derailleur and possibly a left shifter/brake. And my road bike is out of commission until i fix the problem unless I go back to my triple. Just hope I didn't lose out on purchasing the double crank.

If I have to scrap this project, what is the best way to move forward again. Do you just basically have to buy an all new drivetrain to make it work well and by well I mean easy? If this is so I will be looking at SRAM APEX I think unless anyone else has a better cheap Idea. Also for the BB, I have never been certain because I am a novice at bike maintenance, are they all standard diameters on frames? My bike is a 2006 Trek 1500 so I wonder if a modern day crank can be put on the frame.

Thanks again,

Casey
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Old 05-04-13, 11:00 PM
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The most simple method of going from a triple to a double is to remove the inner ring the use only the 2 to 3 function on the lever. But that's not going to make most happy.

As to your bike's compatibility with modern cranks- I think your bike has a traditionally threaded BB. This design still is supported and has a wide range of options. Non low cost though. You need to show your bike to some one with experience and let them determine the options. Andy.
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Old 05-04-13, 11:53 PM
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Problem is that the triple FDs are designed for a max chainring size of 50t and the double FDs won't extend far enough to reach the outer ring. To make this work you need a double 9-speed FD (Sora) and an Octalink bottom bracket with a shorter spindle. The shifters will work fine if you successfully lock out the unused inner ring using the limit screws and use the 1&2 or 2&3 shifter positions.

Or you could go back to the 50t ring and get a cassette with an 11t cog. 53/11 gearing is a leg-breaker and only necessary if you regularly pedal at speeds greater than 37 mph.
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Old 05-05-13, 10:12 AM
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Thanks for the reply Oldobobcat.

So basically like I found yesterday I will have to get a shorter BB and a Double specific front derailleur. I will have to debate if I want to go further on this project.

The main reason I am doing this is for looks because the triple worked fine and I wanted the same gear combination as the people I ride with. I could have achieved this by just doing math and figuring out the gear ratios but I thought swapping a crank wouldn't be so bad and it'd give me some experience with my bicycle which I enjoy. Never fun being scared to take apart a bicycle in fear of breaking something.

Anyways looks like I have some decisions to be made I'll keep you guys updated and thanks for the replies.

Casey
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