Redbullet

I recently found an offer for new Tiagra 4700 (10 sp.) right shifter and rear derailleur, which I used to replace an older 8 sp. mechanism from Microshift (triple).
All good, the new system has better progression (12:26), it is quieter and works ok, apart from “B screw adjustment”. It leaves a large gap between the pulley and the cogs, even if totally unscrewed (1.5 cm to large cog with small ring, or 2 cm from large cog with large ring). This results in noisy and long time shifting. In fact, there is not much difference with “B” totally screwed or totally unscrewed. It is like a weak spring leaves the derailleur to far back, despite B screw adjustment. Being a SRAM user, I never saw such behavior: B screw has a very clear and effective impact on SRAM derailleur position.

Photo with derailleur position (B screw totally unscrewed).





Photo with a normal position of the derailleur if I gently push it forward by hand:




How can I make this derailleur to keep a normal position of 3-5 mm distance from cogs?

KCT1986

Hard to tell based on the pics, but is the RD hanger longer than usual?

Here is Shimano's recommended measurements for road & MTB. L measurement.

delbiker1 

Is the derailleur in the mounting hole at the proper angle? If not, that would affect the adjustment of the b screw.

Redbullet

I don't know and it looks hard to measure, but... I'll try.
The hanger worked very well with the original Microshift 8 speeds derailleur.
But Tiagra B adjustment looks strange to me: between fully screwed and fully unscrewed you hardly can see a difference of a few mm. This might be a result of the fact that the B axle spring appears to have very low tension: I can move the derailleur forth and back with a very gentle push of a finger. By contrast, I need a much bigger force to move a Sram Force derailleur to change the wheel, and even a bigger one for a Rival axs.
Tiagra feels very easily to move, regardless B screw adjustment. It seems to have more than enough room for B adjustment, but no force in the spring to apply the adjustment.

Redbullet

This I don't understand. I simply screwed the derailleur on the hanger, just taking care that B screw is in the position to touch the dedicated "shoulder" to action on it when screwed. B screw does action against the hanger, but it has no real effect.
Or, is there another subtle thing I did not observe?

bboy314

Is the Tiagra derailleur used? Sounds like the spring may be worn out, or need to be cleaned and lubricated.

Redbullet

I bought it as new from the bike shop and it really looks as new and unpacked. I seriously doubt that it was used in any way.

Redbullet

Taking a closer look at your scheme, I wonder whether the 30 to 35 degrees angle is, in fact, bigger on my hanger. Playing with the system, I feel that if I decrease that angle, the derailleur might move forward and decrease the distance to cogs.
I'll have hard time to measure that angle on the hanger, there are no tools for that...

choddo

*abort*

Crankycrank

Is the chain length correct? If horizontal dropouts with adjusters try moving the wheel to the recommended position in KCT1986's post #2

Kontact

Redbullet
Okay, you are confusing some of how this derailleur works, which is not like a SRAM.

SRAM derailleur B screws simply pushes the derailleur back and forth directly. This Shimano derailleur B screw adjusts the spring tension between the mounting bolt and the body. So the screw does not set a position - it just opposes the tension in the pulley cage pivot.

The picture appears to be of a bike in a crossover gear, with the bottom of the pulley cage angled forward toward the crank. If not, the chain is too short. In either case, the chain tension is pulling the derailleur and pulley cage forward, overwhelming the B screw spring tension but also causing the upper pulley to pivot back and down. And that's okay, because it will still shift, but it is optimized for shifting the low cassette gears with the low inner chainring - which will cause that upper pulley to pivot up on the cage pivot.

Additionally, if this is the GS version with the medium cage, the derailleur has capacity for up to a 34t cog, and you appear to have a 25t low cog. That capacity comes from having a lower positioned upper jockey pulley. The SS version is 28t max, which would run closer - but in either case the chain length and gear selection needs to match what you are trying to do.

Post a photo of the derailleur in the small chainring and largest cassette cog.

Redbullet

Thanks for the answer.
It is GS version, because the short version had not enough capacity and it is not recommended for triple crankset. Chainring min/max is 50/30. Cassette is SRAM 12/26, with SRAM chain. The chain is rather too long. If one pair longer, then the derailleur reaches its limit in “small-small” position. I can remove one more pair of links and it will still have reserve in “big-big” position.
I attach here a photo with small ring and large cog position.

Redbullet

No, it is the opposite. The first picture in my first post shows the position of the derailleur in "big-big" gear: the derailleur body is far back and the distance to cogs is too big. The second picture (the same "big-big) in my first post shows that I can very easily push the derailleur body (not cage) forward by hand, toward the position which is closer to the cogs - but when released, it goes back.
To me, this is very strange: I can't see how B screw can make a difference in such a design.

Iride01 

Your close up pics show the issue, but they don't show enough of the possible causes for that issue.

Normally, I'd suggest a pic from the drive side of the bike showing both the crankset and RD. One pic with the chain in the big/big combo and another pic with the chain in the small/small combo. But since Shimano's chain sizing for a 3x front is different than 2x, Perhaps just a pic from the side showing it in the big front and small rear cog will do. Here is their chain sizing for 3x with a 30tooth or less rear sprocket.


https://si.shimano.com/en/pdfs/dm/RD...003-09-ENG.pdf


Is the RD and it's shifter the only thing that changed or did cassettes or rings get changed too?

oldbobcat

I'll bet your chain is so long that it's not pulling any tension on the B spring. Show us what what big-big looks like.

Kontact

You didn't read the rest of my post. You don't check pulley gap in big/big, because when you do that the bottom of the pulley cage rotates forward and the top of the cage rotates back and down. The down part creates more gap. The spec is to adjust gap in the small chainring, because the important part of gap is having enough of it.

Adjust your chain gap in the small chainring.

Redbullet

Thanks for the info and link. The chain was a little longer, so I removed one more pair of links. Angles cannot be shown in pictures, but I attached a photo below. It is still 1-2 degrees on the wrong side (I will remove one more pair, but I don’t think it will change anything).

The problem is the following:
The manual says (page 14) “Mount the chain on the smallest chainring and the largest sprocket and turn the crank arm backward. Turn the B-tension adjust bolt to adjust the guide pulley to be as close to the sprocket as possible but not so close that it touches”.
But it looks that that the derailleur was designed (then manufactured) in such a way that it is impossible for B screw to have any effect, thus, the above instruction can never be performed, and the upper pulley will always remain far from the cogs regardless B screw position. See this, taken in requested “Small ring – Large cog position): It shows that the derailleur moves freely a large distance backward (and forward) before touching the element controlled by B tension spring, thus, B screw that controls the spring can not have any effect.

Redbullet

Yes, I did. I attached then, as an answer, a picture with derailleur position Small ring / Large cog. But even so, B screw has no impact at all on the derailleur position. That is because the body of the derailleur moves freely a long distance backward (and forward), thus, can not "touch" B adjustment. It can be better seen in a clip that I posted to Iride01's answer above: It appears that, by design, this derailleur does not allow B screw adjustment to set upper pulley closer to the cogs, although B screw exists. I wonder whether this is only Tiagra 4700 issue, or also the other Shimano tiers...

Iride01 

If your chain is too long, you can't expect the b-screw adjustment to do anything. Get the chain length correct first.

Redbullet

Can we be sure of that? If I remove 1 more pair of links, it will not be 90 degrees, but maybe 2-3 degrees on the "right side", which will also mean that "big - big" position will stretch the derailleur around maximum. I shall not be able to go back, because chain links can not be added back...

Redbullet

P.S.: When I say "90 degrees" I mean the angle made by the line that passes the centers of the pulleys to the ground. But this line can not go up to the center of the cogs. To do that, a specially tailored hanger for each bike and each cassette would be needed, but I think this is not what Shimano wanted to say...

Kontact

Again, you aren't reading. The B screw doesn't directly position the derailleur. It changes the spring tension, so it will move the position indirectly.

And there is only so close you can get GS derailleur designed for 30t cogs to a 25t low.

But we won't know if that is a factor until you understand the basics of this 45 year old Shimano derailleur design.

Iride01 

If your hanger doesn't put the RD in the same position as Shimano spec'd for RD placement, then 90° to the ground for the pully & jockey wheel alignment might not be reasonable to expect.

Generally, your chain is too long if in the small/small combo there is a sag in the bottom run of your chain and the RD is at it's limits for taking up any more slack. Somewhere between too long and not long enough to allow the RD to go into the big/big combo is your chain length that will give you the best shifting and probably allow you to see some difference with the b-screw.

But understand that the only thing the b-screw is for is to change that jockey wheel position with respect to the rear sprockets. And it can't do that if your chain is too long. So get the chain length and everything else correct first. B-screw is about the last thing that needs to be looked at before taking the bike off the stand and going for a ride.

If you are doing this stuff with the bike upside down, then turn it over!

Also, you seem resistant at giving us a picture where we can see the crankset and RD at the same time. As I said earlier, usually seeing what the RD looks like when in the big/big and then when in the small/small can tell a lot. Right now you have some of us doubting your chain length. Once you get us beyond that, we might come up with other suggestions. IE: your new DR is buggered up and needs to be returned.

Redbullet

I understand your point, but B screw does not move derailleur position at all, not even "indirectly". Finally, I found a lot of complains about this on the internet. Apparently, users had to accepted it as a "given".
Shimano manual says that B screw is designed to adjust the distance between upper pulley and the cassette: "Turn the B-tension adjust bolt to adjust the guide pulley to be as close to the sprocket as possible but not so close that it touches" - see page 14. However, B screw is useless: the big distance between the guide pulley does not change regardless B screw adjustment, although GS variant is advertised as fully compliant to my setup (triple 50 to 30 chain rings, 12-26 cassette).

The above results in poor (late and noisy) shifting performance, although it finally shifts all way of the cassette. I could accept a small drop in performance versus SRAM Force 22 or Rival AXS, but in fact it is much lower, even much lower than low end Microshift 8 speeds. 45 years worth nothing if shifting performance is so poor...

Redbullet

I am not resistant at all, I want this issue fixed. There is such a large free play fore - aft in the derailleur before touching the B control, that I feel B screw does not work no matter what. Please find below 3 positions: Big-Big, Small-Small, Small-Big (the one where B screw should work, but id does not). But again: the very large free play fore - aft that I posted earlier in the clip seems to tell that no matter how much I cut the chain, B screw does not do anything...