Freerojo

I have updated a Cannondale tandem with a Bafang BBS02. Using a lekkie 42 tooth front chain ring allows for a perfect chainline as far as I can see. That is, with the removal of the triple crank, the chainline is right where the middle chainring was. I have a new Deore M592 derailleur (with jagwire index adjuster), new Sunrace 11-40 cassette, new KMC 9 speed ebike chain and a Wolftooth roadlink. I have a 9 speed 105 brifter.

The shift up from the 4th (18t) to the 5th cog (21t) almost never happens, it just wants to hang. I somewhat suspect the derailleur hanger though it looks pretty straight as I look at it and the derailleur line. I can increase the tension and that will make things happen at the expense of almost everything else. I am flummoxed, I would have thought shifting to the center chainline would be the easy part.

Barry2 

Have you set the "B" screw correctly ?
OH, and are you within (or close) to the Capacity of the RD ?
NOTE: As stated on the Wolflink site, it permits a larger max rear cog, but does not increase the Capacity of the RD.

Barry

Ryan_M

Have you checked the condition of the shifter cable?

Iride01 

Looks pretty straight might be just enough to give you issues. Have the hanger checked with a tool. It might just need a bump in the right direction.

By tension, I guess you mean adjusting a barrel adjuster somewhere that is really changing the cable length, not tension. So if adjusting that will mean everything else is messed up, then I'm not sure what to look for except for maybe some frayed cable in the shifters or somewhere in the housings.

You can shift past the 21 tooth and all the other combinations are correct. Or do you not use some of the combos because you've never been able to shift to them? I ask this because I've found in actual face to face conversations that people will tell me that their bikes shift perfectly and in the same breath tell me that they can't shift to certain gear combos. It always leaves me flabbergasted.

FastJake

Lots of possibilities.
- I've never used a SunRace cassette but I know they're typically cheap. Maybe that shifting ramp is poorly designed?
- Chainline should be measured, not eyeballed. But poor chainline shouldn't affect the middle cogs. One of the ends will be worse.
- The rear derailer hanger should definitely be checked with the tool, not eyeballed.
- The RoadLink should be fine but in my experience it can make shifting less precise if the upper pulley is too far away from the cogs. Have you checked the b-tension?
- The long run of the RD cable on a tandem is going to exaggerate any other issues, especially if the bike is setup for full length housing. Replace cable/housing if you haven't recently and make sure all the ends are cut cleanly, housing is routed correctly, etc.

It's possible that two or more of these issues combine enough to cause the problem.

Freerojo

Shift wire is new and goes through housing real easy. Was mostly naked wire before, but needed to put a short section of housing under the BB to facilitate motor placement and send wire to RD. This approximately 6”section is secure.
B tension is set per RD-M592 at about 5 mm
The Bafang motor shifts the chainline out 10mm. The Lekkie Bling Ring 42 chainring brings the chainline back 9 mm. So technically chainline is off by 1mm.
i didn’t think, going to a single chainring that the RD capacity would be affected. Total capacity of M592 is 45.
Seeing that the tandem is 26 years old, the possibility of the derailleur hanger being out of whack might make it worthwhile to order a new one.

FastJake

Even a new hanger needs to be checked. Unless yours appears damaged I wouldn't bother replacing it. I've found that seemingly small changes to hanger alignment can make a big difference in shifting.

Freerojo

I can get up to the 4th cog no issue, jump over the 5 and from there it’s fine too.

Troul 

are there any ramp issues with the cogs? Try swapping the cogs out.

squirtdad

Wild thought, not based on experience but just brainstorming

The 9 speed brifter, how used is it? and if it has has been really well used was it used a lot for 4/5 and 5/6? possible wear at shifter?

Freerojo

the 9 speed 105 brifter has only 3 seasons of use.

Freerojo

the Sunrace cassette is all one unit.

Iride01 

Can you measure the spacing on that cog to the cogs on either side? Or do you have another cassette to try?

Freerojo

I am returning the Sunrace 11-40 9 speed cassette for another one. In the mean time I will put the older cassette on and see if it hangs. It worked perfect before.

Freerojo

Just wanted to close this out. I took off the Sunrace 11-40 and put back the old Shimano 11-30. I was struck by how much I had to reset the limits on the rear mech but it shifted flawlessly. Soooo, my first action was to return the Sunrace for a new one and that’s what I did. But I began to think that there might be some incompatibility between the KMC ebike chain and the Sunrace cassette. So I went with a Alivio 12-36 9 speed, which is ebike rated by the way and that is working well.

squirtdad

thanks for followup, it is always good to know what worked out