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I have managed to bend the rear derailleur on my gt palomar, the gear was not clicking through so I moved it through the gears set off and heard it crunch. The whole arm is bent.
It appears to be a shimano 7 sis dr of some kind. Can someone advise of the correct replacement I can buy. Would a shimano tourney or Altus be the right thing?
Many thanks for your help
As the picture shows the shifter, the derailleur is the bit at the other end, I presume its the shifter that has broken.
Any 7 speed shifter will work. this is a combined shifter so you will need a combined (with brake lever) shifter or you could choose to install a seperate shifter and brake lever.
You will almost certainly need (and be a lot easier) to get new brake and shifter inner cables to install the new levers. The cable installed though the shifter and brake lever then threads back to the derailleur or brakes. Reusing an old cable, is almost always an exercise in frustration followed by installing a new cable anyway. I would install new outers as well when doing a job like this just to be sure they are not a problem. Levers themselves are incredibly reliable, so its possible that the rear derailleur is part of the problem.
Brakes have two cable pull lengths, make sure the lever you purchase matches the brakes on the bike. In this case as the lever says V Brake so any V Brake compatible lever will work.
We don't do product recommendations, but something like ST-EF500-7R2A would be good. If cost is a consideration have a look to see if you have a local bike coop.
Pretty much all 6-9 speed Shimano derailleurs should be compatible. The pull ratio of all of them is the same.
The main concern is that the derailleur "capacity" is enough to take in the slack from the chain when you're in the small-small combination. Looking at your cassette, that's unlikely to be an issue; it doesn't look like it has a very wide range (looks like maybe 11-25?).
Shimano does document the capacity of their derailleurs, so just look up and check before you buy. The capacity needs to be at least the difference in cogs between the smallest and largest sprocket in the cassette plus the difference in cogs between smallest and largest chainring. Some derailleurs have (in addition) limits on the smallest or largest sprocket they can handle. But honestly, I doubt you'll be able to find one which won't work.
Would a shimano tourney or Altus be the right thing?
Either of those, or Claris or Sora, would likely be fine.
An example derailleur that would probably work is the Claris RD-2000-SS:
https://bike.shimano.com/en-US/product/component/claris-r2000/RD-R2000-SS.html
According to the official specs (as listed on that page) It requires at least 25 teeth on your lowest (largest) sprocket, a maximum of 16 teeth difference between your smallest and largest chainring, and has a total capacity of 37. From my limited experience and from reports from others, you can usually go a bit outside the stated specs without any problems, but unless you're running a triple chainring or have a particularly wide-range double I'm guessing that this one would be just fine.
