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I had a crash recently that destroyed my 8 speed sensah reflex rd. I replaced it with a 9 speed shimano sora for a bit of upgrade but after 4 tune ups by the mechanic its still not right. Just so discouraged pls help. I noticed also that my rd hanger is kind of a little bent or not straight enough will this matter? Thank so much in advance...

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I believe you are referring to the shifter, not the front derailleur. The shifter connects to the derailleur with a cable

Sensah Reflex is an 8 speed system with components designed to be interchangeable with Shimano 8 /9 speed.

http://www.disraeligears.co.uk/Site/Sensah_Bicycle_Components_2020_page_6.html

Probably the Sora RD is slightly better quality, not because it is 9 speed but generally Shimano have better manufacturing standards and shifting quality than most other brands, though Sensah doesn't seem to be terrible at all.

There is no difference between an 8 speed and a 9 speed RD so that part is fine. (Often a 9 speed is a more expensive part and made from lighter materials , but that's all)

Given that you still have shifting problems and have identified that the derailleur hanger is bent, it is obvious that that is the source of your problem. So find a replacement derailleur hanger, keep your Sora RD. If you can't find a replacement hanger perhaps you can straighten it, but given your mechanic has failed to do so replacement seems a better option.

https://www.parktool.com/blog/repair-help/rear-derailleur-hanger-alignment

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If the derailleur hanger is bent, it certainly does matter. It is a very common source of shifting problems, particularly after crashes. Even a small visible bend is bad.

No matter how good the derailleur itself is, if the hanger is bent, you won't get good shifting. It should be straightened using a dedicated tool (it can be done without in a coarse way, but not that well) or it can be replaced. The hangers are made to be replaced but can be frame-specific. If you cannot find a spare easily, take it to a bike shop and let it be replaced or straightened.

However, if your mechanic didn't notice the bent hanger, consider that it can be the case that either a) it is not bent after all, or b) the mechanic is not good enough and it is better to take your bike elsewhere.

To answer the title: No, the brand often does not matter between 7,8 and 9 speed rear derailleurs. Just keep the same number of speeds on the shifter and on the cassette. The exception may be some SRAM 1:1 groupsets, Campagnolo, Microshift Advent and some other. If it says Shimano compatible, it should be the same.

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  • Campagnolo is incompatible too, and there are two incompatible types of Campagnolo 9-speed. The wide compatibility between 7-9/10 speed Shimano an exception, not rule.
    – ojs
    Oct 24 '20 at 10:55
  • @ojs Certainly not just Shimano, many other third parties too, SRAM also in those not 1,1, also some no-name or OEM like BTWIN, or indeed, the RD the OP had, Sensah Reflex. Campy is something special for racing bikes and does not really make 7-9 speed groupsets anyway, veloce is 9 speed.. This was a side note only later added to my answer.
    – Vladimir F
    Oct 24 '20 at 13:21
  • Ok, I thought bicycles made before 2000 still exist. My mistake.
    – ojs
    Oct 24 '20 at 14:34
  • @ojs This is about replacement parts for a current cheap bicycle, not about middle-end bikes in the 2000s or high-end bikes from 1990s. Who is gonna buy a Campy 9-speed Veloce (8-speed are really vintage now) for a bike with no-name Asian 8-speed components?
    – Vladimir F
    Oct 24 '20 at 14:36
  • Someone who finds a great deal on eBay and has read that all 8 speed derailleurs are compatible? In the other direction, at one point you could buy 8-speed Dura-Ace cassettes really cheap because it had the reputation that it's incompatible with everything, when actually only derailleurs and shifters were incompatible.
    – ojs
    Oct 24 '20 at 15:34
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The bent derailleur hanger will undoubtedly give you shifting issues. The mechanic should be able to sort that out easily with a special alignment device.

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  • 1
    They are normally compatible. Some are even sold as 7/8/9 speed in one unit.
    – Vladimir F
    Oct 24 '20 at 7:39
  • Sounds good, thanks.
    – MaplePanda
    Oct 24 '20 at 18:24

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