Campagnolo 1 kilogram test of friction in cable

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excel11
Posts: 24
Joined: Fri Feb 22, 2013 4:40 pm

by excel11

When I push the rear derailleur all the way in - the derailleur will snap all the way back to start position. However, when I push the rear derailleur half way in - the spring does not have enough force to bring the derailleur all the way back to start position.

Is this a failure of the test?
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"I got back up and started chasing" - Geraint Thomas

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bikerjulio
Posts: 1900
Joined: Fri Dec 11, 2009 10:38 pm
Location: Welland, Ontario

by bikerjulio

I don't think so. Lets' see what other say.
There's sometimes a buggy.
How many drivers does a buggy have?

One.

So let's just say I'm drivin' this buggy...
and if you fix your attitude you can ride along with me.

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graeme_f_k
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by graeme_f_k

It may be.

Like most springs used in this type of application, the force generated is more-or-less linear across it's intended use-range, but it won't be completely linear so there is some variation (Hook's Law) - this is why when fitting springs, even with the gear mech (or whatever) "opened out" to it's maximum possible extension, the spring still has to be compressed, twisted, etc. in fitting, depending on which spring is under discussion, to pre-load it.

In the 1kg test, release should be done gradually and in a controlled way - if the RD is allowed to "snap" back against the high gear stop, you may get a false "pass" on the test because the force generated by spring tension in the 1t part of the travel is slightly higher higher, plus the admittedly small momentum generated by movement in the system might pull, say, a kink, through, say, the entry into a piece outer before it has "time" to interfere with movement.

In the case of this test, try drawing the RD back to various points along it's travel and releasing it and see if you can identify the point at which the test starts to fail, or whether it fails "absolutely" at any given point - that may give you more information.

If you want to check the RD for consistency (we do this occasionally with some of the older RDs where he spring has to travel in a track or channel which may be worn or damaged), hold the bike front wheel down in the workstand, vertically, insert a gear cable passing it only through the rear section of outer and use a mass hung from that ... you should find a fairly consistent pull of approx 1.1- 1.2 kg across the whole range. The short piece of outer should not introduce more than a few tens of grammes of "drag" and its very unlikely that such a short piece of cable would "hide" a kink or imperfection that would cause a "catch" in the cable travel.
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Head Tech, Campagnolo main UK ASC
Pls contact via velotechcycling"at"aim"dot"com, not PM, for a quicker answer. Thanks!

excel11
Posts: 24
Joined: Fri Feb 22, 2013 4:40 pm

by excel11

Thank you for this new testing of the rear derailleur! I have a very consistent pull across the range of the derailleur when going only through the rear housing.

I have isolated the friction to the housing coming out of the shifter. I tested various lengths of housing coming out of the shifter. I found if I used a shorter piece of housing that did not cross in front of the fork all friction was gone. However, I do not like this look.

My cable and housing are coming out of the side hole of the 2014 SR shifter and not the top hole of the shifter. I assume this should not matter? My handlebars are Time Ergo Force. Do you have any other thoughts on losing the friction?
What happened to you after you fell? - Steve Porino
"I got back up and started chasing" - Geraint Thomas

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