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Old 09-29-10, 06:09 AM   #1
Conti
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Chain jammed between middle and granny rings

Hello,

I bought an old tandem some weeks ago. It's a circa-1980 Gitane tandem. We rode around 500km on it, and even if it's far from perfect (it's a bit wobbly), we really enjoy it.

However, there seems to be a problem with the front derailleur. It's a (non indexed) Simplex. Sometimes (it happened 4-5 times for the moment) when shifting from the middle ring to the granny ring, the chain is jammed between the two chainrings. It happens when I forgot to shift BEFORE an hill, when the cadence is probably too low to shift without any problem.

I think I need to be more careful: I should shift when the cadence is fast enough. However, I also wonder if that problem could come from a worn derailleur (especially the spring).

Some information :
- Chainrings are : 53/42/34
- 5 sprockets freewheel
- Chain size : 1/2 x 3/32
- Drive train setup : crossover front drive (drive chain from the front crankset to the rear wheel, timing chain from the front crankset to the rear crankset)
- The drive chain is quite long, and I'll replace it ASAP since I think it's worn

Here is the Simplex derailleur :
DSC_8932_s..JPG

What's your opinion ?

Thanks.
Nicolas, Paris.
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Old 09-29-10, 09:20 AM   #2
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Park of being a successful captain is to communicate with your stoker. In this case, you need to say "shifting!", she (and you) needs to ease off the pedaling force, and you complete the shift without hassle. It doesn't matter if you're on a hill. You can still give it the extra juice before the shift to keep your momentum and then ease off the force as you shift to prevent chainsuck and the like.

Shifting under load is just not something old systems were capable of coping with.
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Old 09-29-10, 02:45 PM   #3
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I have a similar vintage Gitane tandem. If you have a Stronglight 99 tandem crank installed, there are compatible Sakae Ringyo middle rings with a ramp to help prevent this problem. I may have a couple in my "big box o' chainrings" if you want to try one. Gitane also used TA cranks on their tandems at times, in which case my chainrings wouldn't fit.

If you do replace the chain, don't get one of the modern super-narrow 9 or 10 speed chains as these will exacerbate your problem. I've used SRAM 7-speed chains successfully here.

Regarding the long chain line -- you can mount the drive crank on the rear bottom bracket to shorten the chain run so that a single road chain will suffice. I found the long chain had a tendency to bounce off the tensioner when the cranks were mounted on the captain's bottom bracket. The downside is that the derailleur cables are much longer, and the original shift levers on my tandem (low end Simplex) did not work too well with the longer cables. I soon replaced them with Simplex "retrofriction" levers which work much better.
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Old 09-30-10, 07:31 AM   #4
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Quote:
Originally Posted by nhluhr View Post
Park of being a successful captain is to communicate with your stoker. In this case, you need to say "shifting!", she (and you) needs to ease off the pedaling force, and you complete the shift without hassle. It doesn't matter if you're on a hill. You can still give it the extra juice before the shift to keep your momentum and then ease off the force as you shift to prevent chainsuck and the like.

Shifting under load is just not something old systems were capable of coping with.
You're right, communication is important on a tandem. We try our best to ease off the pedaling force when shifting, and that made a great difference. The jammed chain problem occurred at the beginning, when we weren't really used to our tandem. But it still happens sometimes.

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Originally Posted by JohnDThompson View Post
I have a similar vintage Gitane tandem. If you have a Stronglight 99 tandem crank installed, there are compatible Sakae Ringyo middle rings with a ramp to help prevent this problem. I may have a couple in my "big box o' chainrings" if you want to try one. Gitane also used TA cranks on their tandems at times, in which case my chainrings wouldn't fit.
That's interesting. Could you have a look in your "big box o' chainrings" ? I'm in Paris, but I pay for the shipping, for sure. The middle ring on my tandem has 42 teeth. When the chain jammed for the first time, I had a look at the rings. I was then surprised to do not see any ramp on them. Those rings are a simple plate with teeth, there's nothing to really guide the chain from one ring to another.

Quote:
Originally Posted by JohnDThompson View Post
If you do replace the chain, don't get one of the modern super-narrow 9 or 10 speed chains as these will exacerbate your problem. I've used SRAM 7-speed chains successfully here.
You're right. I measured precisely the drive chain to order the correct size. I ordered a KMC Z30 1/2 * 3/32. It's recommended for 6 speeds cassettes.

Quote:
Originally Posted by JohnDThompson View Post
Regarding the long chain line -- you can mount the drive crank on the rear bottom bracket to shorten the chain run so that a single road chain will suffice. I found the long chain had a tendency to bounce off the tensioner when the cranks were mounted on the captain's bottom bracket. The downside is that the derailleur cables are much longer, and the original shift levers on my tandem (low end Simplex) did not work too well with the longer cables. I soon replaced them with Simplex "retrofriction" levers which work much better.
I already replaced the shifters. I'm not use to shifters installed on the frame. I installed some cheap SunRace Thumb shifters.
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Old 09-30-10, 08:55 AM   #5
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Find a 28T chainring perhaps
stronglight 99 has a small bolt circle ,so flexible chainrings ,
once youve dropped the chain in between the 2 rings
likely you bent them making the gap bigger.
Back in the day.. the other guys..
one of the drilling patterns TA used was to bolt 2 chainrings together with another 6 bolts
much larger than the inner bolt circle.
also offered back then was a separate sub spider to bolt chainrings onto this larger bolt circle

i think the larger was like a 43 and larger tooth ring, whereas the smaller was for a 26 minimum chainring
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Old 09-30-10, 02:56 PM   #6
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That's interesting. Could you have a look in your "big box o' chainrings" ? I'm in Paris, but I pay for the shipping, for sure. The middle ring on my tandem has 42 teeth. When the chain jammed for the first time, I had a look at the rings. I was then surprised to do not see any ramp on them. Those rings are a simple plate with teeth, there's nothing to really guide the chain from one ring to another.
I looked through my chainring collection, but the only compatible rings I found with ramps are 45T. I do have a compatible SR 40T ring, but it lacks the ramp.
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Old 09-30-10, 11:51 PM   #7
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I looked through my chainring collection, but the only compatible rings I found with ramps are 45T. I do have a compatible SR 40T ring, but it lacks the ramp.
OK. Thanks for having a look anyway, JohnDThompson.
I think finding compatible chainrings with a ramp isn't easy, even on the internet. I'll have a look.
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