B Tension Screw Has No Effect?

[bpsmith]

Have been adjusting my derailleurs following the sound advice on Park Tools website. It advises on adjusting the B Tension screw on the Rear, but this appears to have no effect at all on my setup. Any ideas why?

It originally came with an 12-30 cassette, but now has an 11-28 on there. Is this why?

I shortened the chain via the info on above site.

Do I need to be bothered at all, if its not giving me any hassle?

 

[Roadrider48]

The B tension screw moves the top jockey wheel further away or closer to the cassette. Whatever the case may be.
It won't adjust the changing of the gears up and down.

 

[ColinJ]

The B tension screw moves the top jockey wheel further away or closer to the cassette. Whatever the case may be.
It won't adjust the changing of the gears up and down.

True, but adjusting it properly can make the transmission quieter. My gears were sounding noisy so I put the bike on my workstand yesterday and investigated. I found various problems, which I sorted out. There was still a bit of clunking on the biggest 2 sprockets and I could see that the jockey wheel was rather a long way from the bottom of them. I adjusted the B-screw to bring the jockey wheel closer to the cassette and that wrapped the chain further round the sprocket and stopped the noise.

 

[guitarpete247]

I was trying to fettle GF's eldest's Giant Hybrid. The jockey wheel was running on the largest rear cog in bottom gear. So I tried the B-Screw adjustment. No change. Upon close inspection the B-Screw doesn't push against anything, I think he's twisted the RD at some point (he has been on the blue runs at local off road course). He's talking about selling bike so I'm not going to spend hours on it. I think the chain might be a little too long also.

 

[w00hoo_kent]

So what will the symptoms be of a poorly adjusted B tension screw?

 

[ColinJ]

So what will the symptoms be of a poorly adjusted B tension screw?

Read post #3, above ...?

 

[Cubist]

The B tension screw needs tweaking at both ends of the gear range. Set it first when the derailleur is under no tension.

Here the jockey is too far away from the smallest cog,


Now add the derailleur cable. Shift to largest rear sprocket and check the adjustment again. You are aiming for an optimum gap as ColinJ says, where there isn't too much clearance. It needs to be about 5mm away from the bottom tooth of the sprocket.
In this pic there isn't enough clearance, and the chain will foul on the biggest cog when you downshift, making a racket.


In this pic there's just the right amount of clearance for smooth slick changes. Any more gap and the chain won't engage/wrap enough with the sprocket.

 

[w00hoo_kent]

Read post #3, above ...?

So, it just means the chain will rattle a bit but everything will work OK?

 

[ColinJ]

So, it just means the chain will rattle a bit but everything will work OK?

In my case, yes. It was pretty annoying though so I was glad when I made the adjustment.

I think that any significant unwanted noise from a bike is a sign that something is wrong. Every time that I have ignored such a noise, something has either broken or worn out soon afterwards.

 

[bpsmith]

Thanks for the advice guys. If mine appears to being doing nothing, then I gather it's either not pressing against where it needs to or the chain is too long?

 

[ColinJ]

Thanks for the advice guys. If mine appears to being doing nothing, then I gather it's either not pressing against where it needs to or the chain is too long?

If the chain is too long then it will sag in the little-little gear selection because the mech will not be able to pull it straight, but read Graeme's advice above if you plan to shorten it!

It is easy to see if the b-screw is pushing against part of the frame, as it should do.

I didn't know what b-screws were for until I read about them on the Sheldon Brown site. After that, I just put the bike on a stand, adjusted the screw, and observed the results. I was surprised how much difference it made when adjusted properly. I was also peeved that I had spent years with unnecessarily clunky, rumbling/ticking rear mechs!

 

[Stantheman]

Just had a look at my B tension and, even with the screw completely removed, I cant get the jockey wheel as close to the cog as in the above pictures.

 

[bpsmith]

@ColinJ I can't see any post relation g to chain length by Graeme? Does he have a different username?

I have already removed 2 links from my chain in order for it to fit based on the Park Tools site advice. I used the big cog to big cog, without going through the mech, method and 2 links was what seemed right.

I am pretty good mechanically, but err on the side of caution when first trying something out.

The B tension screw has little to no effect presently. Might try manually holding the mech under more tension, to replicate the shorter chain scenario, and test the screw.

I know it should be simple, but sometimes the obvious catches you out.

 

[ColinJ]

@ColinJ I can't see any post relation g to chain length by Graeme? Does he have a different username?

Oops, wrong gearing thread!

This post!

 

[bpsmith]

Oops, wrong gearing thread!

This post!

No worries. Much obliged Colin.