Re: B-tension screw

On 5/21/2025 12:06 PM, AMuzi wrote:

On 5/21/2025 10:53 AM, Beej Jorgensen wrote:

I got a cheap MTB with a Shimano Tourney rear derailleur. The guide
pulley pushes against the cogs while riding.
>
But the B-screw is one of those kinds that (I think) just pushes against
some kind of internal spring. Or at least it's supposed to.
>
Thing is, I can turn that screw by hand and it doesn't feel like it's
pushing against anything for the entire range of travel. The guide
pulley doesn't drop at all no matter the position of the screw.
>
Ideas? Is the thing just broke? It's a little unclear to me how to peer
inside it to see what's up, or if that's a thing you're even expected to
do with a $20 derailleur. :)
>
-Beej
>

 Try slipping the chain off the front, then adjust the top pivot ("B") screw, noting the derailleur body position as you change it. If you are able to see an effect, slip the chain back on and adjust such that the upper roller clears the largest sprocket.
 If screwing that adjuster screw in and out makes no difference, consult your LBS for a quick opinion. Could be an overly long chain, something broken in the top pivot, low gear too large for that version of Tourney, or maybe just a stripped thread in the derailleur body.  A new Tourney (fine product BTW= good value for what it is) is dirt cheap anywhere but you may not even need that.
 

As andrew notes the derailleur body should move when the B-screw is adjusted. It is doesn't, see if the screw end of the screw is actually contacting anything. The b-screw stop in the derailleur hanger might be way out of range or missing completely. This is extremely unlikely, but worth considering on a cheap bike.