AlCastro

Hey All,
Short story, do you know if you can change the length of the rear derailleur cage from medium to long without affecting the performance of the derailleur?

Long story: a mate of a mate borrowed my bike, broke the derailleur and got it replaced and has used it. I think the mechanic has replaced the derailleur with a medium length derailleur not long, as there is heaps of sag in the chain on small chain ring and small cassette. I don't think its b-screw adjustment as derailleur is in a good place when it's in the large cassette gear.
I know that i shouldn't be in small small or large large, but thats not the point. Nor is shortening the chain.

Can't post photos. Im a newb around here.

Russ Roth

Medium cage is only meant for a wider range double where long cage is often a slightly smaller cassette range but works with a triple. A med might handle the difference even if it isn't meant to depending on your gearing. Put it in the big/big, the critical gear for determining if its safe or the der and hanger will be ripped off the frame. If you can remove a pair of links in this position shift to the small/small and see if removing them will take up the slack, if so go for it and it should work fine. If it isn't safe to remove a couple links or doing so won't eliminate the slack then the only proper solution in a new long cage, don't remove links to test or it might result in needing to replace the chain as well.

79pmooney

Are you asking about putting a longer cage on this derailleur with a medium cage? Or are you asking about getting another long cage derailleur and returning to close to what you had before? I'm not clear on what you are asking.

I used to ride SunTour Cyclone derailleurs and swap cages for different gearing setups. With some derailleurs it is not hard but I have no idea what derailleurs out there now you can do that to.

Tell us what you have - bike, chainrings, cassette (or freewheel), what your past derailleur was and what you have now. And what you want to have. (And yes, whatever you tell us, some posters will be quick to tell you you're wrong. Others of us actually want to help you.)

Welcome to Bike Forums!

Ben

cobba

Add another photo to your album with the big to big combo.

It looks like it might be a medium cage, have a look for the model number on the derailleur, if it's says RD-M_ _ _GS it's a medium cage, if it says RD-M_ _ _SGS it's a long cage.

How is the chain length when you're sitting on the bike with the shock sagged?

It might need a long cage, it might need some links removed.

AlCastro

Yeah I am asking can i take the medium cage off the derailleur and put on a large to return it to what it was before. I mean I don't actually know what has caused the sag but this is all i can put it down to.

its a triple chain ring 42-36-26 and wide cassette 11-36. Pivot Mach 4 (last run of the 26', baby!). I think the past derailleur was a long caged XT, definately XT. but cage I don't know. never had any pain with it.

AlCastro

Chubba, Well, checked it, unfortunately its neither GS or SGS. It says RD-M... VIA

Sitting on the sadle in big big seems to pull the derailleur more forward. eek!

cobba

What numbers are on the derailleur, RD-M????

dedhed

RD-M (what else?) should be numbers here like 780 or the like.

JohnDThompson 

Provided you can find a long cage that will easily mount on your current derailleur, it ought to work. I've done it with Campagnolo, Simplex, and SunTour derailleurs BITD.

Atlas Shrugged

No problem. I replaced the cage on my latest generation R9100 series Rear Derailleur with a GS cage from a Ultegra. Works great no issues.

daverup 

Is it possible that when your mate broke your rear derailleur, he also damaged the chain?
If he replaced the chain without setting the correct length, it would look like what you show in your pics.
The master link is visible and fairly simple to disconnect.
Use Sheldon Brown's method to check the chain length, https://www.sheldonbrown.com/derailer-adjustment.html

AlCastro

Cobba, unfortunately I didn't take the number down. I decided to take the bike to the mechanic who 'fixed it'. Over the phone he said yeah you can add a long cage to it without a problem. I don't know, still want a second opinion. As the spring tension for the cage should be dictated by the lever, or cage length.

AlCastro

Dedhed. Yah, unfortunately I didn't jot it down and took the bike to the mechanic who 'fixed' it. When it comes back from the shop, i'll post the part type number on here.

AlCastro

Atlas Shrugged, cool. Are the derailleur cages you have switched out and put in different lengths? with the new one being longer?

AlCastro

John,

Good to hear it's worked for you. If it is all shimano components and XT range, Would there be any reason why the wouldn't fit?

JohnDThompson 

Chances are good with the same manufacturer and model and similar vintage, where cage mounting specifics are likely to be consistent across different cage lengths. I've put Simplex SX-410 long cages onto Simplex SX-660 bodies, Campagnolo Rally long cages onto Campagnolo Nuovo Record bodies, SunTour Cyclone long cages onto Cyclone short-cage bodies, etc. The closer the donor is to the recipient, the better the odds of it working. But designs change across manufacturers, models and over time, so no guarantees.

Atlas Shrugged

Yes, it allowed me to use a 34 or a 36 Cassette without any other modifications. Had enough capacity to go from small-small to big-big. Very cheap as well.

rydabent

Yup wrong RD for a triple.
And again----------------the "B" screw is NOT for chain tension. That is one of the most misunderstood thing abour RDs!!!

Bill Kapaun

Likely it's already a "mountain" RDER and your search is pointless.