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Can't determine my cage size (RD)

Old 08-23-13, 12:05 PM
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Can't determine my cage size (RD)

So I bought a new 34t cassette, and I got a new RD off of eBay. The ad said it was a long cage, but when i go 34t in the back and my small gear in the front the wheel of the RD rubs. I'm pretty sure my chain length is right. How can I tell if I have an SGS? I looked on the arm of the thing and it just says RD-M737. It doesn't say GS or SGS or anything.
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Old 08-23-13, 12:10 PM
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Even SGS models is rated at 32T.

GS is 28T
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Old 08-23-13, 01:10 PM
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what's it rubbing (I assume you mean the little pulley wheel is contacting the bottom of the cassette) and did you adjust the B screw when you installed it?

You may get better advice if you post on the mechanic's subforum.
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Old 08-23-13, 01:26 PM
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As you have found out large cog capacity does not necessarily go up with the cage length, which can be increased without changing the upper pulley position. All the long cage does on it's own is wrap more chain, such as for the use with a triple chainring. It probably is a GS if advertised as such - pretty easy to tell visually. You can play with chain length and B-tension position (Google shift to large cog for explanation of options) to exceed normal specs, but if a GS you are way beyond, so unlikely to work.

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Old 08-23-13, 01:50 PM
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Yep, 34 exceeds the designed capacity of that particular derailleur. If you are disciplined enough to never go into big-big, with careful chain length and b-tension manipulation, it *may* work, but either way, you are running mismatched parts.
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Old 08-23-13, 06:04 PM
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Originally Posted by Pricey Socks
So I bought a new 34t cassette, and I got a new RD off of eBay. The ad said it was a long cage, but when i go 34t in the back and my small gear in the front the wheel of the RD rubs. I'm pretty sure my chain length is right. How can I tell if I have an SGS? I looked on the arm of the thing and it just says RD-M737. It doesn't say GS or SGS or anything.
Sounds like you need to tighten your b-bolt.

If its already bottomed out, you can take the RD off and screw in the b-bolt the other way so the head hits the little shark fin on the derailleur hanger to get a little more action.

Mismatched parts, yes, but I bet you can make it work.
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Old 08-23-13, 07:56 PM
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They made both GS and SGS versions of the ol' XT-level rd-m737. Post up a pic, and we'll be able to tell right away. From your problem, I'd wager it's a GS, but you may just need to mess with the b-screw, as others have mentioned.

Keep in mind that both the SGS and GS versions of the rd-m737 were designed for a 32t max cog; the SGS simply has more capacity. If you have a GS and you're running a mtn triple up front, you'll want to avoid big/big, and to may have issue with excess slack in small/small. These combos should be avoided regardless.

Last edited by surreal; 08-23-13 at 08:01 PM. Reason: clarification
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Old 08-24-13, 09:57 AM
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Thank you guys for your responses. I have determined through the advise here and deeper digging that the max capacity for that particular model is 32 even on the SGS. I ended up getting a brand new (not used) Deore RD from my LBS.
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