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Drivetrain component mismatch-XTR RD-971

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Drivetrain component mismatch-XTR RD-971

Old 03-22-14, 07:21 PM
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ClarkinHawaii
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Drivetrain component mismatch-XTR RD-971

I've got a mismatched system here that I'm trying to troubleshoot.

The RD I have is stamped Shimano RD-971. (designed for 9 gears, but that's irrelevant at this point)

How can I tell if it is the SGS or GS version?

I am trying to use this RD with a Shimano 34-11 cassette.(10 gears, but that's irrelevant here)
According to the Specs from Shimano, both versions are supposed to handle a 34-tooth max cog:
https://techdocs.shimano.com/media/te...9830607913.pdf

According to the same Spec/Instruction sheet, "3. Low adjustment--
Turn the low adjustment screw so that the guide pulley moves to a position directly
in line with the largest sprocket." When I try to do this, the guide pulley bumps into the largest cog and fails to clear it by about 4mm. This is after I have screwed the B adjustment screw all the way in, which I believe is supposed to provide max separation of the guide pulley from the cogwheel.

I don't understand why it doesn't clear, since it's within the max capacity specified???? Please dispel my confusion . . .
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Old 03-22-14, 07:57 PM
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Jeff Wills
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The only difference between a GS and SGS derailleur is the length of the derailleur cage. SGS is longer than GS. Most (perhaps all) Shimano mountain derailleurs will shift to the 34 tooth cog.

One thing that you didn't say is whether the bike is completely put together. If you try the B-screw adjustment before installing the chain, the top pulley will run into the big cog as you are describing. This can also happen if the chain is too long.
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Old 03-22-14, 08:24 PM
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It was completely put together and I rode it 11.5 miles this morning with no problems except that the shifting with the largest cogwheel was sometimes a little hinky. So I decided to investigate.

The first thing I looked at was the RD--I took off the chain and went to the Shimano Instructions linked in my first post above.

I didn't get any further than this situation of the guide pulley bumping into the side of the 34T. The low adjustment procedure indicates that it should clear without the chain on. When it wouldn't clear, I then screwed the B down all the way (without the chain) assuming it would help.

The chain is the right length.

OK, I just unscrewed the B all the way and now the guide pulley will just fit under the 34T if I match up the cogs on one with the valleys on the other. So you are right!

So now I can set the low adjustment properly (it was just a little too tight), then reassemble with the chain and readjust the B, correct?

Then I can address the next problem, which is that my triple crank in conjunction with the cassette, exceeds the Specs recommended for the RD.

What I have now:
max chainring dirrerence = 50-26=24
max cassette cog diff = 34-11=23
total drivetrain capacity = 24+23=47

total rated drivetrain capacity for the RD971 is 43 for the long cage and 33 for the shorter cage. I'm pretty sure I have the long cage, but I'm still a little over at 47 vs 44. Am I gonna crash and burn or what? Thanks for your help!

EDIT: this is on a road bike frame that I'm converting into a tourer. Using Dura-ace 10-speed bar end shifters, 105 front triple derailleur and 105 triple crank both 5600 series. Is there another derailleur which can handle my 47T capacity needs? Should I think about changing the RD?

Last edited by ClarkinHawaii; 03-22-14 at 08:32 PM.
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Old 03-22-14, 10:08 PM
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Shimano capacity specs are conservative. You can often exceed them by 3-4 but there is less room for error on the chain length if you do. I've exceeded the capacity on my Shimano Dura-Ace by 4. I sized the chain just long enough to be able to run the big-big combo (even though I never use that combo intentionally). It ran with a little sag in the small-small but I never use that combo anyway.

Looks like RD-M751, RD-M571, RD-M511, RD-M760, RD-M580, RD-M761, RD-M581, RD-M531 capacity spec is 45 (SGS)

Last edited by Gonzo Bob; 03-22-14 at 10:18 PM.
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Old 03-22-14, 10:10 PM
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If the 44T max is critical, I could just swap the present 26T granny for a 30T granny like this and be within specs. Certainly cheaper than buying another derailleur. But is it necessary?
Shimano 105 FC-5603 30t 10-Speed Triple Chainring
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Old 03-22-14, 10:39 PM
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Originally Posted by ClarkinHawaii View Post
total rated drivetrain capacity for the RD971 is 43 for the long cage and 33 for the shorter cage. I'm pretty sure I have the long cage, but I'm still a little over at 47 vs 44. Am I gonna crash and burn or what? Thanks for your help!
Oh heck no. I have a 52-42-24 triple crank and a 11-34 cassette with a Shimano SGS derailleur. 51 tooth total difference! It works fine- the chain is a little loose in small-small, but you'd never use that gear anyway.
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Old 03-22-14, 10:58 PM
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OK, well, it looks like just properly adjusting what I now have should fix the problems. Thanks for all your help!
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