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Bosch Performance "surging"

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Old 08-09-18, 02:30 PM
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Bosch Performance "surging"

I recently purchased a Trek Super Commuter 8s with the Bosch Performance motor. I live in a very hilly area and I've been riding it every day. No problems at all, very natural feel. Today I tried a much stepper hill and ended up in the lowest gear on the cassette and in Turbo on the motor. I currently have 125 miles on the bike. At first it was fine but it started surging. I wasn't able to maintain a steady cadence, and if I paused in pedaling, the motor would continue to pull. Then, when I would begin pedaling again, the motor would lag initially before surging again. Once I cleared the hill, it continued this behavior in a number of gear and motor combinations. I immediately took it to my dealer and they said they put it through a diagnostic test. It showed no errors. It feels, to me, like an issue with the pedal sensor.

Has anyone experienced anything similar?
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Old 08-09-18, 04:23 PM
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This may, or may not apply to your situation, but it's worth mentioning. We all have a dominant hand, and leg, which is stronger than the other. You may unconsciously be applying more force with your strong leg which will cause a surge.
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Old 08-09-18, 05:19 PM
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The other thing is, following that hill, I returned to a portion of my normal ride and the problem continued through that.

When I stopped to push a crosswalk button, the bike pulled forward a couple of extra feet.

On every ride, in every situation before, it felt like the motor responded to me. In other words, I supplied input and the motor responded. Now it feels as if it is trying to get ahead of me. Several times, the bike acted as if self propelled.
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Old 08-09-18, 06:08 PM
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Only time I had a similar problem (the motor supplied continuous power and could be "stopped" only with the brake cut-off), the problem was the torque sensor or that's what I was told when I sent it back to the manufacturer.
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Old 08-10-18, 08:40 AM
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definitely sounds like a torque (pedal) sensor

did your dealer bother to ride it? Bug them again
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Old 08-10-18, 09:12 AM
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They said two people rode it. Neither on a hill, of course. I made them keep it and test it on a hill. I've been in contact with Bosch and plan to talk to Trek today.
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Old 08-11-18, 08:07 AM
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Keep on them and they will fix it, I'm sure. Your mistake might have been telling them it started doing it on the flat, but they still should believe you.
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Old 08-11-18, 09:45 AM
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FME, Trek has excellent CS; I went to the hierarchy once and was amazed at how responsive they were.
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Old 08-11-18, 07:59 PM
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I went back to the lbs today. They said they could discover nothing and they rode nine miles. I took it out and found nothing, either. It is powered by a computer, so it's possible something went wrong that ride. Perhaps I should've rebooted. I'll be riding tomorrow morning and put Red through the paces on our normal route.

I was ready to start making calls and sending emails. I didn't really care for the response - except from the techs. They were excellent and seemed to really care. The shop owner? Not so much.
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Old 08-14-18, 08:32 PM
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Surging can be caused by the speed sensor not picking up correctly. The magnet on the rear wheel needs to line up between the Bosch logo and the name on the frame sensor. Common mistake is to line it up with the round part. If the speed sensor doesn't record, it will automatically shunt the system into minimum assist, which is quite jarring, and can behave consistently with what you are describing.

Incidentally, the first thing the Bosch diagnostic program does is offer to install any extant updates...which will over-write/clear any error codes--it can happen, if the technician is not paying attention. Food for thought.

The torque sensor in the case could be damaged, but it is quite well protected. Consider the external issues, first. If it comes to the drive unit, the shop likely isn't allowed to open it, anyway--only Bosch can without the system recording a fault (and yes, it can tell when you open the case).
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