A friend of mine recently brought over a Trek 820 with SRAM 3.0 shifters and derailleurs. Bike could no longer shift at the rear derailleur. Upon inspection I found the mount for the B-tension screw had broken and the screw was lost. So, I couldn’t see any way to fix it, so replacement was the only option.
Doing my research, I found that this is a SRAM specific derailleur and has a 1:1 cable pull ratio. So, I looked at what options SRAM has now for 7-speed and found the X3 and X4 should be compatible. A shop locally had an X4, so I went off and bought it. It seemed to install fine until I had to adjust the limit screws. I couldn’t get it to reach all 7 speeds. If the L limit was adjusted so it wouldn’t go into the spokes, it wouldn’t go into the smallest cogs. The only way to get it to go into the smallest cogs was to back out the L limit, but then it would shift over the smallest cog into the spokes. Nothing I tried would make it work.
My only guess was something was wrong with this derailleur, so I brought it back to the shop. They double checked it should be compatible, checked everything was aligned, and still couldn’t get it to work either. 3 mechanics tried while I was there. Eventually they decided to order an X3 and had me leave the bike.
Get an X3 or find a 3.0 for replacement!
A few days later they called me and said the bike was fixed. The X3 installed and worked fine. So, if you need to replace a SRAM 3.0 you should get an X3 or find a 3.0 replacement if you can find one on the used market. My experience with this bike makes me think the X4 doesn’t really work with a 7 speed. Good luck with your repair.
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Frugal Average Bicyclist 
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Well done.
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Thanks
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