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Short cage RD with triple front?

Old 09-30-11, 01:31 PM
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Short cage RD with triple front?

My used group package has arrived this morning.
This is all the stuff: https://www.flickr.com/photos/klenger...7627712361128/
My question is whether I will be able to use the Dura-Ace short cage RD to go with that triple front and one of those two cassettes? Will the RD be able to pick up the chain slack?
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Old 09-30-11, 01:41 PM
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IIRC, triple chainrings typically need a long cage rear derailleur.
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Old 09-30-11, 01:54 PM
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Originally Posted by bike_boy
IIRC, triple chainrings typically need a long cage rear derailleur.
I was afraid of that! I was hoping to use that triple, but still enjoy the crisper shifting of the short cage RD. Well, so be it.
I may have to put that triple crank on Ebay, and look for a double to replace it. Can I then use the 12-27 10-Speed cassette?
One more question:
The BB turns, but does not spin. Is that just because the grease is old and stiff?
Can I recondition that or should I buy another one?

Last edited by Again; 09-30-11 at 01:57 PM.
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Old 09-30-11, 02:13 PM
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That DA derailleur looks like a long cage to me.
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Old 09-30-11, 02:23 PM
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You'd have to get a "compact" double chainring/crank to somewhat equate to a triple. You will tend to shift back-and-forth between compact's chanrings though. I have a short cage RD, 12-27 cass, and 50/34 compact crank.

However, a long cage RD is a cheaper alternative than going compact.
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Old 09-30-11, 02:28 PM
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AFAIK, BB's I've held (DA, Ultegra internal ones) can be turned, but do really spin. My guess is once assembled with cranks in frame, the weight of the cranks and seating bb shell helps with the ability to make 'em spin.
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Old 09-30-11, 03:04 PM
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Originally Posted by Puget Pounder
That DA derailleur looks like a long cage to me.
Funny - for some odd reason I just assumed it would be a short one. But it even makes better sense to be a long, since it came as a group.
I took some shots for you to get a good look:

What do you think?
Attached Images
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100_1309.jpg (92.3 KB, 13 views)
File Type: jpg
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Old 09-30-11, 03:17 PM
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Originally Posted by bike_boy
AFAIK, BB's I've held (DA, Ultegra internal ones) can be turned, but do really spin. My guess is once assembled with cranks in frame, the weight of the cranks and seating bb shell helps with the ability to make 'em spin.
I see. But would it not be a good opportunity to recondition it while it is out? Is that a tough job?
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Old 09-30-11, 03:43 PM
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Shimano is designing to sell replacements, not serviceability.
External Bearing assemblies are fairly low cost.
Is that a tough job?
you have time, bike shops don't, so then a replacement is installed.

can you even see where a seal would come out?

now Phil Wood , and Chris King have aftermarket External BB
they May have designed theirs for serviceability.

Last edited by fietsbob; 09-30-11 at 03:47 PM.
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Old 09-30-11, 03:54 PM
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I've only reassembled FSA MegaExo BBs. you just pop the seals off to the cups/bearing cartridges and then clean them out with some solvent and a tooth brush. Squirt new grease in and it will be (kind of) good as new. Never done it with the Shimano ones though.
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Old 09-30-11, 04:23 PM
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OK then, if I do choose replacement, should I go with a cheapo like this: https://www.ebay.com/itm/200620958320...84.m1423.l2648
or with the Shimano: https://www.ebay.com/itm/2011-Shimano...item3369914e17

Last edited by Again; 09-30-11 at 04:36 PM.
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Old 09-30-11, 04:40 PM
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You can't use a GXP BB with a Shimano crank. The left bearing's ID is 22mm, not 24mm like with a Shimano. Get the Shimano BB.
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Old 09-30-11, 04:41 PM
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I was wondering!
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Old 09-30-11, 05:53 PM
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Yes, you can use a short cage rear derailleur with a triple crank set and a 12x27 cassette (total teeth = (53-30) + (27-12) = 38) BUT you will have to avoid the granny ring with several of the smallest cogs. Shimano claims the short cage RD-7800 will wrap 28 total teeth so you would have to limit the granny to the 21 tooth or larger cogs.
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Old 09-30-11, 05:54 PM
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105 would be fine too.

https://www.google.com/products/catal...ed=0CEYQ8wIwBg#
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Old 09-30-11, 06:14 PM
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Originally Posted by HillRider
Yes, you can use a short cage rear derailleur with a triple crank set and a 12x27 cassette (total teeth = (53-30) + (27-12) = 38) BUT you will have to avoid the granny ring with several of the smallest cogs. Shimano claims the short cage RD-7800 will wrap 28 total teeth so you would have to limit the granny to the 21 tooth or larger cogs.
Yes, one would have to pay a bit of attention to the gears in such case. Anyway, it seems to be a long cage, which settles the case.
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Old 09-30-11, 06:46 PM
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I think I'll get the Ultegra BB, it's only $30 and sure to be right for the crank I have.
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Old 09-30-11, 06:58 PM
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Originally Posted by fietsbob
now Phil Wood , and Chris King have aftermarket External BB
they May have designed theirs for serviceability.
I got a Chris King BB. I love how you don't have to remove or replace any seals to service the BB-- Just use their grease injector tool to flush out old contaminated grease while injecting fresh clean grease at the same time.
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Old 09-30-11, 07:23 PM
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Originally Posted by Puget Pounder
That DA derailleur looks like a long cage to me.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

+1 this.

I don't foresee a problem.
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Old 09-30-11, 10:02 PM
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The instructions you'll need should be around here.
https://techdocs.shimano.com/techdocs...&bmUID=iS193Zw

Make sure the crank came with all the spacers like #10 and #16
https://techdocs.shimano.com/media/te...9830621036.pdf

Not to mention the spacer for the cassette
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