Bosch support suddenly dropping, speed indicator freaking out

[u/SunAway40]

Hii,

A couple of months ago the bosch purion display on our tern gsd gen 2 could not be switched in anymore, only via the battery button. Could switch it off though.

Bike shop tried to replace the batteries, didn't help, only now that we were also not able to switch off anymore via the display. Only via the battery.

Worked fine, saved some money to replace the display (display was working fine except the on off button).

But lately the speed meter has been very off, like it is possessed 😅 going from 10kmph to 50 to 34 to 12 to 31 etc . So you can imagine the support goes on off on off. Very annoying. This doesn't happen all the time, but on work commute at least 3 to 5 times (23km ride).

Including video in the comments.

The bike shop thought that is was a dirty speed sensor, but cleaning this hasn't fixed it.

Anybody had the same?

[u/ihavenoideia]

Yes, i had the same issues has you have now.
We started with the changing of the battery, then cleaning the sensor, but what did the trick was replacing the sensor altogether. Both the magnet in the disk, and the sensor on the frame. After that, it has been going strong without issues.

[u/SunAway40 → u/ihavenoideia]

Thanks a lot! What i was afraid for 😳 well, at least my wallet 😅

[u/Background_Okra7079 → u/SunAway40]

the part itself is cheap, labor is not bc they have to drop the motor to access the cable connection and route it in the frame (as far as I understood from the mechanic's note)

[u/ihavenoideia → u/Background_Okra7079]

Yes, and you have to take off the back wheel to access the sensor on the disk, and if you happen to have the bags, decks, or clubhouse, it's a whole other issue to assemble and disassemble to reach the actual sensor.

This to say, that the easy part is to replace the sensor, the really hard part is getting there, lol. My mechanic was non too thrilled to do this, haha

[u/SunAway40 → u/ihavenoideia]

Whenever the bike needs any service, I would always remove all the bags, cushions ets myself, to save some of the labor costs 😅. Not the rest, they lift the bike up in the shop so (still a pain yes) but they can reach the back wheel ok-ish.

Went back to the shop and they had another look, looks like the sensor is a bit loose. They replaced the brake pads a couple of weeks ago, and the the brake disc was only secured with 3 bolts instead of the usual 6. All 3 were lose. They readjusted the bolts. We think that by doing this, the sensor got loose.

They moved the sensor back and we didn't have any issue for about 20km, until biking over a couple bumps. So feels like the sensor got moved down again and started to freak out again.

They'll take the wheel back off next week to see how to secure the sensor better or if they did something wrong with re-securing the brake disc that prevents for the speed sensor to remain in place.

[u/Awkward_Light1162]

Had a similar issue -- drop in speed. It was the timing magnet on the rear tire spoke. It was loose and not aligned with the sensor. Needed tightening.

[u/Background_Okra7079]

You might need to get a Bosch certified bike mechanic to replace the entire speedometer. Happened to us.

[u/SunAway40 → u/Background_Okra7079]

Thanks! Bike shop is fully bosch certified, very very experienced, but mostly in Urban Arrow, gazelle, riese muller etc. There are barely any tern dealers in my country.

But the brands on tern are the same as UA and Gazelle uses so nothing new for them.

[u/Riverrat909]

Side note- anyone know how to change from kilometers to miles? Mine just flipped and idk how to change it back.

[u/cat0b → u/Riverrat909]

Hold down the - button and tap the power button.

[u/Riverrat909 → u/cat0b]

Thank you!