Is this short cage?
06-17-18, 08:25 AM
#1
Yo
Thread Starter
Is this short cage?
Hi all, is my rear derailleur short cage? If it’s not, will a short cage work in it’s place?
06-17-18, 08:45 AM
#2
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Nope. Whether a short cage would work or not is all about chain wrap so the first thing you should do is calculate the difference in teeth by subtracting the sum of big front and big rear from the sum of small front small rear. Then check your numbers against the manufacturer's spec. Also be aware that RDs have limits on max and min cog size.
06-17-18, 08:57 AM
#3
Yo
Thread Starter
Thanks hoop, this brings me to another ?, if I buy a short cage derailleur can I swap parts from my old one to my new one and make it work? I think mine has a short in it and I found a short cage for $110 is why I’m asking.
06-17-18, 09:20 AM
#4
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Basically you dial in on Shimano your present RD, & it will tell you the range (teeth) it will operate over, several factors like you have not stated what is on the front end (crank) is it a double or triple, & what range are these, its not rocket science but you do need to follow the ranges of what all component parts are designed to operate at, Shimano like others tend to use a group set concept so all parts are matched. Below 10 speed, you could mix & match without to much problem. So as a basic start point get the model number of all your drive system components, & see how they match up, there are some very good Shimano / charts manuals that show the compatibility between various model #
06-17-18, 09:46 AM
#6
Senior Member
06-17-18, 11:09 AM
#7
Non omnino gravis
That's a GS (medium cage) on the bike..A short cage won't be super happy about having to deal with that 32T cog.
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06-17-18, 03:56 PM
#8
Yo
Thread Starter
Ok thanks guys, another? Is the circled part the cage? And if so can I buy the short cage and swap parts around and make it work?
Last edited by MikeOK; 06-17-18 at 06:19 PM.
06-17-18, 06:01 PM
#9
Senior Member
Generally with Shimano you can swap cages. Take a look at the underside of that derailleur knuckle where the cage is attached. You are looking for a small hole and a set screw inside, maybe 2.5mm size screw, unscrew that little guy all the way and pull it out. Not sure if they all still use that method of attaching the cage, but they certainly used it up until 10spd on the mountain derailleurs.
06-17-18, 07:25 PM
#10
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It looks like the cages are interchangeable here. It looks like you need the whole axle assembly too, as they are different part #'s SS to GS
https://si.shimano.com/pdfs/ev/EV-RD-6870-3641A.pdf
https://si.shimano.com/pdfs/dm/DM-UL0001-04-ENG.pdf
https://si.shimano.com/pdfs/um/UM-5XW0B-003-00-ENG.pdf
Manuals & Technical Documents
https://si.shimano.com/pdfs/ev/EV-RD-6870-3641A.pdf
https://si.shimano.com/pdfs/dm/DM-UL0001-04-ENG.pdf
https://si.shimano.com/pdfs/um/UM-5XW0B-003-00-ENG.pdf
Manuals & Technical Documents
06-21-18, 09:33 AM
#11
Yo
Thread Starter
In case someone searches for this, the problem turned out to be a short in my derailleur as I suspected. I took it to the bike shop and they changed a couple wires, but that didn’t fix it. So how I isolated it was I unplugged both shifters and both derailleurs then plugged them back in one at a time every few hors until one of them ran down my battery. Shimano is covering it under warranty.
06-21-18, 09:36 AM
#12
Banned
calculating..
distances between pulleys can be measured..
you may have a triple capable RD, the cage longer for the slack,
created by the difference between ...
(big + big ) - (small + small) in tooth count ..
such as, 53,39, 30 and 11-27 thats 53+27 - 30+11 [ 80 - 41 = 39 ]
for 11/32, 50/34, (50+32)-(34+11) 82 - 45 = 37.. so not much less .
.....
you may have a triple capable RD, the cage longer for the slack,
created by the difference between ...
(big + big ) - (small + small) in tooth count ..
such as, 53,39, 30 and 11-27 thats 53+27 - 30+11 [ 80 - 41 = 39 ]
for 11/32, 50/34, (50+32)-(34+11) 82 - 45 = 37.. so not much less .
.....
Last edited by fietsbob; 06-21-18 at 09:55 AM.
06-21-18, 01:34 PM
#13
Clark W. Griswold
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Shimano has been good with warranty for me. They replaced my 6870 FD (few questions asked) which broke due to synchro shifting and then me getting off the bike (the pressure of hoping off to see what happened, did it in on the beginning of a 3 day ride). I cannot see much of the bike but from what I can see and what you have said it looks like it could be a pretty swell bike (I have a similar set up on mine and also the frame looks like Ti as well)
