72andsunny

Still trying to get the old tandem running smoothly. For as long as I can remember, the upper jockey wheel has rubbed the big rear cog (when I’m on the small chainring).

It’s raining, so I decided to try to do something about it. The B screw was put in backwards, which leads me to believe I must have had a shop try to fix the problem in the last 15 years. I pulled it out slightly, which briefly fixed it, but after cleaning up the chain and adjusting cable tension, it has returned.

Here’s what I’ve tried so far, mostly in order.

Pulled B screw out, and put in from correct side. B screw appeared too short, so I went to Ace hardware and bought a longer screw. Put that screw in from correct side, but at a certain point, the angle becomes wrong and it stops doing anything useful. Tried reversing new longer screw. The head doesn’t stat where I want it to go. Checked chain length, which for 53/34 and what I measure as 17.5 inch chain stay is correct at 57 links. Park Tool says my chain does not need replacing. I was thinking of giving up and taking it to a bike shop, but as there are almost no tandems on the island, I’m not expecting much for my $80.

Any thoughts on what I should try next? I was thinking of getting a B screw with a much larger head and then screwing it in backwards. Was wondering if I’d have any more luck with the derailer off the bike.

unikid

Can you clarify what you mean by "the head doesn't stay where I want it to go"? Is the screw turning after you set the length? If so, then maybe try some Blue Loc-tite on the threads?

akexpress 

What size is your rear cassette. You might want to get a road liink or goat link from wolf tooth components to move the derailleur down and back. Very common with the new large cassettes. An inexpensive solution to the problem

100bikes

Was your gearing customized?

It sounds like your chain is a bit(1 link or maybe 2) long. The derailleurs you use have limits of chain wrap
and customizing this might not have addressed this issue.

If your tandem had an eccentric bottom bracket to allow the connecting chain to be adjusted, you may want to look into this area.
If the eccentric has been re oriented, it would allow the chain to, in effect, become longer.

Photos would be a great help in diagnosis.

akexpress 

most Tamdems have the eccentric in captains bottom bracket so it does not affect chain length to the derailluers

sapporoguy

+1 this solution. I had that problem with a 12-36 cassette. Long B-screw turned in was at wrong angle where it hit dropout. A Wolf Tooth Road Link solved it:
https://www.wolftoothcomponents.com/...ducts/roadlink
It says 10/11 sp but works fine on our 9sp.

72andsunny

Here's a photo of the b screw in the reverse position. If the head would stay under the purple tab, all would be good. I did go out to try some larger head screws with minimal improvement. The problem appears to be the angle of the screw.

72andsunny

Everything is stock. This is at least the second cassette, but I've always replaced with exactly what was on the bike. I've considered taking out a link, as I believe it would solve this problem, but would likely cause a new problem should I end up on a big chain ring/big cog combination.

72andsunny

This is how I'm picturing Santana's set up while I'm at work.

72andsunny

11/34...this was probably a big cassette in 2003.

Road link looks like what I need, except there website says it won't work with long cage derailers (which I have) and triple chain rings (which I also have).

72andsunny

As above: their website says medium cage derailers only and no triple chain rings. Do you happen to have either of those? Thanks!

sapporoguy

I have triple chain rings, and pretty sure I have a long-cage derailleur, and the link works fine on an 11/36 or 12/36.

72andsunny

Thanks, I'll give it a try for $25. My brain hurts a little right now; did you have to add links to the chain?

akexpress 

it will work fine on a triple It is more of a factor of the large cassette

sapporoguy

Did you want a cassette larger than 36? I put in the Wolftooth when I switched up to 12/36 from 11/34.

akexpress 

I doubt you will need to add chain links

100bikes

Has the tandem fallen over? The photo makes is look like the alignment of the B adjustment screw is off
center to the stop.

This could be the problem, as the jockey pulleys could be closer to the cog after a fall and the alignment similar to what is in the photo.

Carbonfiberboy 

I think it's completely normal for the jockey wheel to be directly under a 34T cog, using a normal MTB RD. The B screw won't do anything about that. It's fine. I don't see the issue. The spring in the RD determines the pressure of the jockey wheel against the chain, no matter where it is.

100bikes

Agreed that derailleur spring determines the float of the derailleur with both pulleys in the same vertical plane as the (largest, in this case) cog.
I still contend that the dropout alignment matters. With the large gear range tandems sometimes have, this would be an important factor.

The small chainring and large rear cog combination is in the middle of the range of tensions that rear derailleur needs to
handle(small front chainring/ small rear cog being the the most difficult for the derailleur to handle - carrying a lot of the
chain wrap/weight as well). The shifting may not be affected through the ability of jockey pulleys to float around a bit.

The photo shows that there is a clearly a misalignment. A tandem with a forged dropout such as this should/would definitely
have the hanger in alignment to accept the B screw to hit dead center from the factory/builder.


Check the most outward edge of the derailleur for any indication of damage;
and
Check the hanger for paint buckle

From the posted photo, it is difficult to determine any /all issues.

Two photos that would help the group diagnose the issue:
One from behind the bicycle , showing the rear derailleur with the chain on largest cog in rear and smallest ring in front, to show alignment;
Photo showing the face of the derailleur from the side having stated that it is all original, except the cassette.

72andsunny

I guess the issue is it makes the gear combination pretty close to unusable.

72andsunny

I’ve had it for over 15 years. Bill McCready has personally knocked my bike over more than once. Usually when we crash, I try to land as hard as possible on my left shoulder...

sapporoguy

Just to make sure there's no confusion (which I'm sure you didn't intend!): The B screw may not affect whether it's directly under, but it *does* determine the gap between the big cog and the jockey wheel. So if the jockey is rubbing the big cog, it's the B screw's job to adjust the gap between them.
From Sheldon Brown: "If your derailer has a B screw, then you install the new cassette, shift to the large cog, and adjust the "B" screw so that the jockey pulley doesn't hit the teeth on the large cog. See picture below for a fully screwed in B screw. Check Sheldon's page about derialer adjustment for more B screw info."
https://www.sheldonbrown.com/deakins/lowgears.html

sapporoguy

Good vid! Mine did exactly that. So I added one of these, and that fixed it:

Carbonfiberboy 

Why is that? My 26 X 34 worked perfectly with the jockey wheel directly under the center of the cog. I'm using a 40T now with an extender, so I can't send a photo. But my B-screw didn't do anything to change that either. See the post right below this one.

Carbonfiberboy 

Didn't work on my 34T, either. Position of B screw seemed to have no effect at all. Bike shifted perfectly, though I was frustrated that it didn't look like the pictures said it was supposed to look. The reason mine worked might have been the specific RD, a M952 XTR Mega 9 long cage.