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Crank Replacement for 1980s Motobecane Nomade?

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Crank Replacement for 1980s Motobecane Nomade?

Old 03-03-19, 10:28 AM
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dfreichert
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Crank Replacement for 1980s Motobecane Nomade?

I hope I am in the right area of the forum, if not,let me know. I am tuning up a bike for a friend, and I am unable to get the front derailleur to switch gears when riding. In the repair stand, it shifts fine, but under any load the chain will not change rings. The chain and freewheel were changed last year, so after some reading, my guess is the front crank is worn. Does anyone have any suggestions for a suitable replacement? Also, so I replace the bottom bracket while I'm at it, and if so, a recommendation for that? Not trying to break the bank, as I believe the bike isn't worth more than $150 dollars. I am unable to post a link to pictures or upload pictures due to not having 10 posts.
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Old 03-03-19, 11:12 AM
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I think you mean that the front chainring needs to be replaced, not the crank itself. But before we discuss replacing chainrings, let’s talk about the shifting. Can the derailleur shift from the big chainring to the little ring? Can it shift from little to big? Or neither?

As to the chainrings, look at the teeth. Are there signs of wear? If so describe them. Are the chainrings bolted to the crankset arms? What labeling is on the crank?
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Old 03-03-19, 11:43 AM
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Originally Posted by dfreichert View Post
I hope I am in the right area of the forum, if not,let me know. I am tuning up a bike for a friend, and I am unable to get the front derailleur to switch gears when riding. In the repair stand, it shifts fine, but under any load the chain will not change rings. The chain and freewheel were changed last year, so after some reading, my guess is the front crank is worn. Does anyone have any suggestions for a suitable replacement? Also, so I replace the bottom bracket while I'm at it, and if so, a recommendation for that? Not trying to break the bank, as I believe the bike isn't worth more than $150 dollars. I am unable to post a link to pictures or upload pictures due to not having 10 posts.
If anything worn out chainrings shift better. That is not your problem. I recommend you don't replace anything.

99% chance it's an adjustment issue. The derailleur may be too high (very common), misaligned, bent slightly, or otherwise badly adjusted.

For starters make sure that there is one penny distance between the FD cage and the outer chainring when the chain is in the small chainring. Then make sure the outer plate is parallel to the chainrings. Sometimes a slight flaring out at the back works. Depends on the FD. Then of course check the limit screws and the cable tautness.

No derailleur, especially a vintage one, is really going to shift under load, especially a front. Ideally the chain should be moving but with no load. Modern derailleurs are better at shifting while under load, but it is still not a great idea.
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Old 03-03-19, 12:03 PM
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Originally Posted by Salamandrine View Post
If anything worn out chainrings shift better. That is not your problem. I recommend you don't replace anything.

99% chance it's an adjustment issue. The derailleur may be too high (very common), misaligned, bent slightly, or otherwise badly adjusted.

For starters make sure that there is one penny distance between the FD cage and the outer chainring when the chain is in the small chainring. Then make sure the outer plate is parallel to the chainrings. Sometimes a slight flaring out at the back works. Depends on the FD. Then of course check the limit screws and the cable tautness.

No derailleur, especially a vintage one, is really going to shift under load, especially a front. Ideally the chain should be moving but with no load. Modern derailleurs are better at shifting while under load, but it is still not a great idea.
Thank you for the feedback. I should clarify, when I say under load, I mean just if I'm riding it at all, vs being in the stand. The FD has been a suspect for me, so I'm going to try the penny test. I'm not quite sure exactly what you are looking for with it though, is there an image I can view? Is it from the bottom of the cage to the teeth of the outer chain ring (and if so, I'm assuming penny thickness). Any feedback would be great.
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Old 03-03-19, 12:14 PM
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What type of front derailleur? The Simplex derailleurs often seen on those bikes are notoriously poor. I swapped my wife's out for some Suntour components I had laying around and the shifting was much better.

Last edited by kross57; 03-03-19 at 12:17 PM.
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Old 03-03-19, 12:16 PM
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Originally Posted by dfreichert View Post
Thank you for the feedback. I should clarify, when I say under load, I mean just if I'm riding it at all, vs being in the stand. The FD has been a suspect for me, so I'm going to try the penny test. I'm not quite sure exactly what you are looking for with it though, is there an image I can view? Is it from the bottom of the cage to the teeth of the outer chain ring (and if so, I'm assuming penny thickness). Any feedback would be great.
Look here for the basics:

https://www.parktool.com/blog/repair...eur-adjustment

There's other more advanced tweaks for old front derailleurs, but if you get the basics covered, it should shift at least OK.
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Old 03-03-19, 12:58 PM
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Originally Posted by Salamandrine View Post
Look here for the basics:

<removed by dfreichert due to limited post history>

There's other more advanced tweaks for old front derailleurs, but if you get the basics covered, it should shift at least OK.
Salamandrine,

Thank you for the link. Adjusting the height (it was a little too high), I am now able to get into the larger chain ring on the front pretty consistently if I am in the lower gears on the freewheel (of course, that's not an ideal gear setting). If I am on the highest gear in the rear, I can now get into the front chain ring if I am going downhill. I am going to try flairing the back of the FD cage out a hair or two to see if that helps any. Looking at the FD cage, I think it's pretty petty up/bent and might require replacement.
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Old 03-03-19, 01:01 PM
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Originally Posted by kross57 View Post
What type of front derailleur? The Simplex derailleurs often seen on those bikes are notoriously poor. I swapped my wife's out for some Suntour components I had laying around and the shifting was much better.
It is a huret FD. I'm not expert, but it seems at least a little bent up. Using Salamandrine's advice, I was able to get the shifting to work a little more consistently going downhill, but that's about it. If I decided to look at a replacement, do you have any you could recommend or link here? I have replaced one before in a bike repair class I took at a co-op.
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Old 03-03-19, 01:05 PM
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Originally Posted by Salamandrine View Post
Look here for the basics:

There's other more advanced tweaks for old front derailleurs, but if you get the basics covered, it should shift at least OK.
Salamandrine,

Thank you for the link. Adjusting the height (it was a little too high), I am now able to get into the larger chain ring on the front pretty consistently if I am in the lower gears on the freewheel (of course, that's not an ideal gear setting). If I am on the highest gear in the rear, I can now get into the front chain ring if I am going downhill. I am going to try flairing the back of the FD cage out a hair or two to see if that helps any. Looking at the FD cage, I think it's pretty petty up/bent and might require replacement.
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Old 03-03-19, 01:52 PM
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Originally Posted by dfreichert View Post
It is a huret FD. I'm not expert, but it seems at least a little bent up. Using Salamandrine's advice, I was able to get the shifting to work a little more consistently going downhill, but that's about it. If I decided to look at a replacement, do you have any you could recommend or link here? I have replaced one before in a bike repair class I took at a co-op.
Just about any modern or ancient front derailleur will work for an old Nomade. Motobécane itself used Japanese dérailleurs so you could use an older Suntour or Shimano part, or of course you could try a new one. And Huret and Simplex both made very good front dérailleurs if you want to keep things French.
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Old 03-04-19, 12:21 PM
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After fiddling with the FD for some time, I compared it to a working one on another vintage bike and determined it was definitely bent. I decided to bite the bullet and order a new one and a set of new shifter cables as well. Once completed, I'll report back.

Thank you all for the advice, it was extremely helpful.
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Old 03-09-19, 10:17 AM
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After replacing the FD and a new set of shifting cables, the bike is shifting like a dream. Thanks for all the help.
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Old 03-09-19, 10:45 AM
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Originally Posted by dfreichert View Post
After replacing the FD and a new set of shifting cables, the bike is shifting like a dream. Thanks for all the help.
Super! What FD did you put on it?
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Old 03-09-19, 10:52 AM
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Originally Posted by kross57 View Post
Super! What FD did you put on it?
I decided to keep the look and feel of the bike the same and found a NOS Huret for cheap on Ebay. Very pleased with how it turned out. This was my first re-cable without assistance, next project is to re-cable my wife's old 86 Schwinn Sprint.
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Old 03-09-19, 11:32 AM
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Originally Posted by dfreichert View Post
I decided to keep the look and feel of the bike the same and found a NOS Huret for cheap on Ebay. Very pleased with how it turned out. This was my first re-cable without assistance, next project is to re-cable my wife's old 86 Schwinn Sprint.
Nice choice and nice work. The old Huret dérailleurs look kind of crude but work quite well, IMO.
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Old 03-09-19, 01:58 PM
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this
from RJ the bike guy may be of use
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Old 03-09-19, 02:00 PM
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or
for a more vintage FD
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