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Di2 DA7970 rear derailleur cage spun around
Last Post 10/05/2014 01:33 PM by 79 pmooney. 5 Replies.
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6ix

Posts:485

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10/04/2014 03:49 PM
Wish I knew how to post a picture but I'll just have to explain. Removed my derailleur today and it looks very, very strange when sitting in the table. The cage appears to be spun around 180 degrees and effectively is facing backwards. I can rotate it back around to where it naturally would be and can definitely feel the spring fighting. It was perfectly fine until I took it off the bike. It doesn't look quite natural to say the least!
79pmooney

Posts:3178

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10/04/2014 06:26 PM
This sounds like an old school problem. Virtually all the old derailleurs had a post that screwed onto the cage right behind the pivot that would keep the cage from lifting above roughly horizontal. So when you pull the wheel, the cage rotates back until that post hits a stop on the derailleur body. These "posts" had a screwdriver slot at the outboard end so in effect they were just a long screw. Go look at any of your other bikes and you will see what I am talking about. You can ride the bike just fine without the screw/post but as soon as you take tension off the chain by removing the wheel, the cage will unwind just as you describe.

It's a fair bet that you can rob that post off an old Shimano derailleur. To see if my guess is right, look for a small threaded hole on the outboard cage about 1mm outside the pivot. If you see it, wind the cage back up, replace the wheel and "borrow" a another screw/post off an old derailleur.

Ben
Inferno7

Posts:344

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10/04/2014 07:38 PM
Six, www.tinypic.com. Upload then cut and paste
6ix

Posts:485

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10/05/2014 08:41 AM
Maybe the picture will show now: https://www.dropbox.com/s/q4olfujf1hhwocu/2014-10-04%2015.43.11.jpg?dl=0

Thanks to Ben for his suggestion. I'll go see about that tiny screw.
6ix

Posts:485

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10/05/2014 09:30 AM
Yup, Ben is right. That's the screw that's missing. No clue how that could have happened but it's gone for good. Any idea on how to find a replacement? I'm searching everywhere for a blow-out diagram of an RD7970.

Again, thanks for your help!!!
79pmooney

Posts:3178

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10/05/2014 01:33 PM
Try an old derailleur. Shimano may well have kept those screws the same model to model to save tooling and inventory costs. If you don't have one, call a few shops. Old, crashed derailleurs are a great source for them.

Shimano should offer replacements that QBP or other distributors carry or can obtain. Contact a Trek/Shimano shop. This screw has been falling off derailleurs and getting lost for at least 40 years.

If you cannot find anything, you could probably make one from a longish (1.5-2.0 cm) screw and a sleeve/tube. Bring the derailleur to an Ace hardware and see what you can find. You will be able to see how long the tube needs to be looking at the derailleur body. A small washer might be needed to get the screw head to sit properly on the tube. Get a screw long enough to go through the tube and thread fully into the cage. You may have to cut it to clear the chain. If the tube is significantly bigger than the screw, semi tighten the screw, then rotate the derailleur until the tube hits the stop, letting it sit off center on the screw so the cage rotates as far up as it would with the smaller diameter intended screw/post. Then tighten down and ride!

And it hurts your bike zero to not have the screw. Just a pain in the a** every wheel change. You might be able to jam a stick in the cage before pulling the wheel and save some of the hassle. (Maybe a popsicle stick or tongue depressor, something that you can stash in your toolbag.)

Ben
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