Is the pin between plates at the bottom of RD pulley arm necessary?

ajmitchell
ajmitchell Posts: 203
edited May 2018 in Workshop
Hi, on the dura-ace 6800/9000 RD there is a pin at the bottom of the pulley plates/cage (jockey arm) connecting left and right (just below bottom jockey wheel) on the SRAM red 22 there is no pin, just a flap of metal. I notice most aftermarket carbon plates dont have these pins so I am guessing a connecting pin is not strictly required. My reason for asking is that if I install at larger jockey wheel (eg 15t) it snags with this pin. I don't really understand the function of this pin, is it to stop the chain unwrapping from the bottom pulley wheel in some circumstances? Thanks for advice.

s-l300.jpg

Comments

  • fenix
    fenix Posts: 5,437
    I'm sure they had a good reason for putting it there. If there wasn't they wouldn't have it.
  • veronese68
    veronese68 Posts: 27,785
    I think the pin is there to confuse people about chain routing so it makes a horrible noise when they do it wrong. It may serve some purpose in keeping the chain where it should be, but I don't think it is massively important.
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  • figbat
    figbat Posts: 680
    Possibly helps keep the chain in place when there's no tension in the RD, like when the rear wheel is off?
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  • sungod
    sungod Posts: 17,313
    same function as the tab on sram, it helps stop the chain from coming off under extreme conditions
    my bike - faster than god's and twice as shiny
  • thistle_
    thistle_ Posts: 7,217
    Veronese68 wrote:
    I think the pin is there to confuse people about chain routing so it makes a horrible noise when they do it wrong. It may serve some purpose in keeping the chain where it should be, but I don't think it is massively important.
    No, that's the pin/tab halfway up the plate :D
    I have 1 where the chain goes over it and another where the chain goes under it :roll:

    If the OP is putting a bigger jockey wheel on, he probably needs to check that the new chainline doesn't foul the middle pin either.
  • svetty
    svetty Posts: 1,904
    If you're the sort of person who thinks that it is worth spending - often serious - money on aftermarket, over-sized jockey wheels then you probably are also likely to try the cage without that pin. Let us know how you get on :)
    FFS! Harden up and grow a pair :D
  • ajmitchell
    ajmitchell Posts: 203
    Svetty wrote:
    If you're the sort of person who thinks that it is worth spending - often serious - money on aftermarket, over-sized jockey wheels then you probably are also likely to try the cage without that pin. Let us know how you get on :)
    bigger jockey wheel with ceramic bearing is £4.
  • fenix
    fenix Posts: 5,437
    Isn't that cheaper than a standard jockey wheel ? Where are you sourcing this magic ?
  • keef66
    keef66 Posts: 13,123
    Running as I do 10 year old 4500 and 5600 kit I'd have thought that a RD9000 rear mech would be hard to improve on, no? Does it not already have ceramic bearings??

    Instinct tells me that sticking in a £4 oversize jockey wheel and removing pins that Shimano presumably deem necessary might be a backward step in several directions.

    But it's your bike / money, so do post some pics when you've done it.
  • sungod
    sungod Posts: 17,313
    a chain getting bounced off could end up causing a lot of damage, rd might end up in the wheel, on a really bad day it could get you killed
    my bike - faster than god's and twice as shiny
  • ajmitchell
    ajmitchell Posts: 203
    Fenix wrote:
    Isn't that cheaper than a standard jockey wheel ? Where are you sourcing this magic ?

    rather not say yet because they are untested and I don't want to give a recommendation..... but they are very easy to find and have down a lot in price in last few years.
  • ajmitchell
    ajmitchell Posts: 203
    edited May 2018
    sungod wrote:
    a chain getting bounced off could end up causing a lot of damage, rd might end up in the wheel, on a really bad day it could get you killed

    Yes this is an important point. So you think that pin/link/flap is there as a safety measure? I am inclined to agree but strange that so many aftermarket pulleycages even the most expensive versions do not appear to have this connector. As a little experiment if you push forward on the RD (reducing tension to zero) the chain does not flop onto this connector...so even if the RD lost spring tension it doesnt seem an issue. I am not arguing it has no purpose, I am just struggling to see when it would be effective. Another perspective is to examine the the inner surface of this connector for wear and it doesnt seem to show wear even on an old bike only dirt.....meaning its there for irregular occassions/mishaps?
  • PhilipPirrip
    PhilipPirrip Posts: 616
    Fenix wrote:
    Isn't that cheaper than a standard jockey wheel ? Where are you sourcing this magic ?
    Aliexpress has alu ones with ceramic bearings starting around that price so I imagine there'll be Chinese sellers on Ebay as well.
  • keef66
    keef66 Posts: 13,123
    On cheaper mechs with simple pressed steel side plates these things are tabs bent from one plate or the other. They do not link the 2 plates together so they are nothing to do with the strength or stiffness of the cage, so I can only assume they are there for chain retention. They are definitely not there as an aid to threading a chain through a mech, because they make it a proper pain in the @rse.

    Some vintage derailleurs lack them completely, so they may not be functionally crucial, but I'd not risk it myself. Cars of the same vintage had no seatbelts...
  • fenix
    fenix Posts: 5,437
    I think I'd stay with original kit. Isn't the savings something like 1 watt ?
  • keef66
    keef66 Posts: 13,123
    Fenix wrote:
    I think I'd stay with original kit. Isn't the savings something like 1 watt ?

    I was thinking the same myself when I blundered into the Ceramicspeed website via Weightweenies. 1500 Euros for a replacement derailleur cage with 3D printed jockey wheels the size of the London Eye.

    WTAF is going on there?? It's more than I spent on either of my bikes and it's not even a complete rear mech.

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