Thorn Cycles Forum
Technical => Transmission => Topic started by: Chris M on December 31, 2013, 12:39:20 pm
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Hi All
I'm at the last stages of building up my Club Tour, just the brake and gear cables to be fitted. I'm just fitting the chain but need some advice about cutting it to length. I've wrapped the chain around the largest front and back sprockets and was going to add 1" to that but that would put two outer plates together; looking at the photo, the only option seems to be to leave 1.5" and just take off the last link.
I was wondering if this is going to cause any problems or am I missing something obvious?
Cheers
Chris
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http://www.youtube.com/watch?v=JY1XxU_y2u0
this vid shouls sort it chris.
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Cheers jags, seems to confirm what I thought; leave it a touch longer as they are the only available inner plates.
Thanks mate.
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no problem chris always good idea to have a few of those magic links in the tool box. ;)
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Wow look how clean that chain is, and clean fingers as well, is this picture a Photoshop export.
Peter
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Wow look how clean that chain is, and clean fingers as well, is this picture a Photoshop export.
Peter
I hope he hasn't cleaned the factory lube off the chain. That's the good stuff!
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Andre did you ever find out wxactly what that lube is. ;)
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Wow look how clean that chain is, and clean fingers as well, is this picture a Photoshop export.
Peter
I'll let you into a secret; It's a brand new chain straight out of the wrapper. ;)
I've been trying to sort the gears out all day but have now given up for the night. I think I may have the wrong rear derailleur, I've already had to buy a new front one because of the chainstay angles.
So, how does this work?
I measured the chain and cut it to right length. I'm using the chainset off my Trek it's Shimano XT M-771-K (26/36/48) and at the rear a new XT M770 Cassette (11-34T) alongside an XT M772 Shadow derailleur. Exactly the same as I ran on my other bike. After fitting the chain and cable I noticed a large amount of slack (chain really hanging low) when on the smallest chainring and smallest sprocket at the rear, not a combination you would use but useful to see how the rear derailleur is taking up the slack, which it obviously wasn't. After checking the chain length a few times and that the RD was fitted correctly I still couldn't work out what the problem was.
Finally, a closer look at Shimano Tech Docs shows that the derailleur I have is a GS rather than the SGS I thought I had (it was fitted by the LBS). I could only identify it from the SGS one by the different cut outs on the back plate. This would explain the slack chain as it's capacity is only 33T against the 45T I need. The question is, how did it work on the other bike? There's only 5mm difference in the chainstay lengths, the other bike being the one with longer chainstays.
I can pick up an SGS M772 tomorrow from the shop but I'm still confused how it worked on one bike but not another.
Anyone got any ideas?
Cheers
Chris
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Andre did you ever find out wxactly what that lube is. ;)
It's some relatively light oil (by internal combustion standards) loaded with wax to give it extra cling, but I don't know the exact formulation because the manufacturers hold that secret. That stuff's so good, one wonders why they don't market it. It may be though that it is forced into the interstices of the chain by pressure. Thing about chain lube is that what you can see is wasted -- at best it prevents corrosion that is merely cosmetically undesirable; the work is done on the rollers where you can't see, which is why you should lube only one side of the chain, so the lube can flow through (if you lube both side, you could form an unlubed air bubble in the middle that will wear your chain right fast).
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I'll let you into a secret; It's a brand new chain straight out of the wrapper. ;)
I've been trying to sort the gears out all day but have now given up for the night. I think I may have the wrong rear derailleur, I've already had to buy a new front one because of the chainstay angles.
So, how does this work?
I measured the chain and cut it to right length. I'm using the chainset off my Trek it's Shimano XT M-771-K (26/36/48) and at the rear a new XT M770 Cassette (11-34T) alongside an XT M772 Shadow derailleur. Exactly the same as I ran on my other bike. After fitting the chain and cable I noticed a large amount of slack (chain really hanging low) when on the smallest chainring and smallest sprocket at the rear, not a combination you would use but useful to see how the rear derailleur is taking up the slack, which it obviously wasn't. After checking the chain length a few times and that the RD was fitted correctly I still couldn't work out what the problem was.
Finally, a closer look at Shimano Tech Docs shows that the derailleur I have is a GS rather than the SGS I thought I had (it was fitted by the LBS). I could only identify it from the SGS one by the different cut outs on the back plate. This would explain the slack chain as it's capacity is only 33T against the 45T I need. The question is, how did it work on the other bike? There's only 5mm difference in the chainstay lengths, the other bike being the one with longer chainstays.
I can pick up an SGS M772 tomorrow from the shop but I'm still confused how it worked on one bike but not another.
Anyone got any ideas?
Cheers
Chris
Chris,
I don't think the 5mm would make any difference at all, have you adjusted the b tension screw, it sounds like your RD is not taking up all the slack. Do you have any pictures of the whole setup it may help.
All the best.
Peter.
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Cheers Peter
I've adjusted the B tension screw so that the jockey wheel is 5mm from the sprocket when on the largest sprocket as per the tech docs. I've also tried 'bottoming out' the b screw just to see if the slack goes; it doesn't.
Two pictures with the b screw in the correct position, for what it's worth, the chain runs up and down the sprocket faultlessly when the pedal is rotated and shifter operated. I've removed the front derailleur for the time being while I sort this out.
Cheers
Chris
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Other picture:
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chris thats ok ,try putting the chain on big ring up front and higest gear (13) at rear your chain should be nice and tensioned, click up a few cogs you should still be ok .
now change to middle ring and go down another cog 17 to 23 small ring for lowest gears.
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Chris,
What rear cassette is installed, it looks to me like the large rear sprocket is too big for the mech, unless the is an adjustment you are missing.
Peter
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peter i had that same rear mech its fine up to 32 i think only think i didn't like about it there is no barrel adjuster on it so i installed some on cables at sti leavers work spot on.
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Cheers jags, the gears run up and down fine but still the slack.
Peter, it's a 11-34T cassette worked fine before.
I'm tempted to take a couple of more links off the chain.
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I just removed another inch from the chain and it still hangs slack when on the smallest chainring and sprocket. I'm convinced it's a GS cage and I should be using an SGS cage. I've had this set up on my other bike for a couple of years with no problems but it got me thinking and I can't remember a time when i actually used the 'granny' ring so it's possible that it's always been like that and I never realised.
Luckily, Cyclesurgery are open tomorrow and they have the SGS in stock just down the road in Holborn.
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Chris,
I agree it looks like the RD you have simply does not have enough capacity for the setup you have.
Looking at the tech doc
https://www.google.co.uk/url?sa=t&source=web&rct=j&ei=-MrDUveFF8yihgfEzYCgBA&url=http://www.bike-components.de/bedienungsanleitungen/2011/shimano/mountain-bike/deore_xt/rd-m772.2.pdf&cd=4&ved=0CDUQFjAD&usg=AFQjCNGeGgfbHAEBssTH8Gj4pjszK-829A&sig2=povxoQ1dYgXU0KQlYczNBA (https://www.google.co.uk/url?sa=t&source=web&rct=j&ei=-MrDUveFF8yihgfEzYCgBA&url=http://www.bike-components.de/bedienungsanleitungen/2011/shimano/mountain-bike/deore_xt/rd-m772.2.pdf&cd=4&ved=0CDUQFjAD&usg=AFQjCNGeGgfbHAEBssTH8Gj4pjszK-829A&sig2=povxoQ1dYgXU0KQlYczNBA)
The total capacity of the SG is 33 and when you are in 48 / 11 you need a capacity of 37 so I feel you need an SGS.
But that does not explain how it ever worked.
Peter.
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Thanks Peter
Looking at the back plate in the tech docs; the cut outs on the GS backplate match the ones on mine. I spent a bit more time last night trying to get it to work. By removing another inch from the chain and bottoming out the B tension screw, I can just about make it work although the shifting isn't nowhere near as good as it should be. I think I could have made it a bit smoother with time but at 2am I'd had enough. I'm popping out soon to get a new RD, same model but SGS, I'll take this one with me just to check the cages against eachother.
I read that the GS has a cage length of 83mm and the SGS a cage length of 100mm, I'm not sure where the actual cage is measured from though. Measuring mine from centre to centre of the jockey wheels gives 80mm.
Hopefully a new RD will sort the problem for me as I'm itching to get it set up and ride it.
Thanks for the help mate, much appreciated.
Cheers
Chris
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I've just returned from the shop and can confirm that I had the wrong RD.
I had my other bike converted by the LBS to all XT a couple of years ago and they fitted the GS rear derailleur alongside a 26/36/48 chainset and 11-34T cassette. I just assumed that everything would work together on my new bike.
It makes sense now why it used to take me ages to adjust the gears to run smooth whenever I carried out any work on it.
For comparison the photo below shows the new RD M-772 SGS on the left against the old one, M-772 GS.
Thanks for all the help everyone and sorry for all the questions.
Cheers
Chris
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Well done Chris you will be up and running in no time, but the LBS were lucky to make the GS work.
Peter.
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good stuff your that bit wiser now ;)
glad you got sorted happy cycling.
jags