Slow gear change under drive mode

Idgtech

New Member
Region
United Kingdom
Hi all. Just fitted a Bafang BBS02 mid drive to my 29er. With drive off, the bike goes down and up the gears without issue. However, when motor is on, the bike goes down the gears ok, but is sluggish to go up the gears. Sometimes the gear change just doesn’t happen. Click again and it will often jump two gears. I have a gear sensor fitted. I notice that if I back pedal 1/4 turn it drops into gear fine.
Any ideas if I can adjust this issue out?
 

AHicks

Well-Known Member
Region
USA
City
Snow Bird - Summer S.E. Michigan, Winter Gulf Coast North Central Fl.
Hi all. Just fitted a Bafang BBS02 mid drive to my 29er. With drive off, the bike goes down and up the gears without issue. However, when motor is on, the bike goes down the gears ok, but is sluggish to go up the gears. Sometimes the gear change just doesn’t happen. Click again and it will often jump two gears. I have a gear sensor fitted. I notice that if I back pedal 1/4 turn it drops into gear fine.
Any ideas if I can adjust this issue out?
The shift sensor, especially a freshly installed one, might be a little "draggy" on the cable (especially as compared to the way it shifted before the sensor was installed). It requires the cable to bend quite a bit as the sensor does it's job. When going "up" through the gears (going from larger to smaller gears), the spring is in play, as it is the sole force pulling the derailleur to the next gear. If that spring is weak, it's going to make the derailleur act as you describe.
 

Idgtech

New Member
Region
United Kingdom
Thanks for the response. As the shift sensor is in place with motor on test and motor off test, I am doubtful it is the cause of the problem.
The spring could be though. With motor on I could imagine tension in the chain making it harder for the spring to have an effect. Are these interchangeable with stiffer springs?
 

Idgtech

New Member
Region
United Kingdom
Solved: I found the problem with gear change. The motor was very close to the frame and slightly loose. When in drive mode, the motor was trapping the gear cable between motor and frame. The chain wheel driving forward was causing an opposite reaction in the motor increasing the clamping effect on the cable. That’s why it was not showing when not in drive mode. I have added a spacer between motor and frame and tightened everything up.
 

PedalUma

Well-Known Member
Region
USA
City
Petaluma, CA
Good. This would happen to me before I learned to always run the housings over the bottom bracket. This is especially important with electrical. If the power shorts from a crimp it is bad news.
 

m@Robertson

Well-Known Member
Region
USA
Yeah I had this happen with my Envoy, whose internal cable routing exited just ahead of the motor housing and got pinched accordingly as it ran back. My solution was a hunk of rubber between frame and motor to move the motor away from the down tube just a hair. Found the right thickness playing with the shifter and motor position until it moved ok and then made the spacer, which was rubber mastic tape balled up to the right size.
 

PedalUma

Well-Known Member
Region
USA
City
Petaluma, CA
On one Specialized through frame that pops out exactly on top of the motor at the BB, I had to expand the exit and cut a slot into the bottom bracket shell for the hydro hose to fit. The rider was 100 pounds and had three months to live. Saying 'No' was not an option for me. Riding was her final wish. I was able to use a longer shift housing and run it over the BB to the right.
Her Bianchi was stolen and I met her posting a flyer about it at a LBS. I found out she was dying so a bunch of us did a Go Fund Me. We got her a new bike and I did the conversion. https://www.pressdemocrat.com/artic...e-bicycle-stolen-from-cancer-patient-in-peta/