Speedo reading intermittent

[Josey Wales]

Hi,

I have a 2019 Decoy. It is a great bike, but I do have a small issue with the speedo.

If I pedal along a flat road about 12 mph, then stop peddling, the mph will slowly drop, then suddenly drop to half speed about 5.5 mph. Then it's very random, if I continue to not pedal, it may jump back up to the correct speed, it may drop to zero, it may jump up then down again. If I start peddling it will always jump back to the correct mph.
I think it all started after removing and replacing the battery. But then I did some jumping, so it could of been that as well.
BTW I only clean my bike when it's really dirty, then with a sponge and never upside down. The battery contacts look brand new and have a thin smear of dielectric grease on them.
I'm pretty sure it's not the speed sensor as waving a magnet over it gets a response. It could be the wire is fractured though.
Anyone else had this and fixed it?

 

[ichauchtt]

Hi,

Clear case of broken speed sensor. I had the same, next thing that will happen is probably a W011 error. You need to replace the sensor and you need to drop the motor to do so. You will find more information on how to do it in this thread:

How to drop motor of YT Decoy?

I need to access the speed sensor cable on the motor for....reasons....and it seems that the motor needs to be dropped to get access to that due to the decoys super stealth design. Anyone have a walkthrough on how to do that?

www.emtbforums.com

 

[Josey Wales]

Hi,

Clear case of broken speed sensor. I had the same, next thing that will happen is probably a W011 error. You need to replace the sensor and you need to drop the motor to do so. You will find more information on how to do it in this thread:

How to drop motor of YT Decoy?

I need to access the speed sensor cable on the motor for....reasons....and it seems that the motor needs to be dropped to get access to that due to the decoys super stealth design. Anyone have a walkthrough on how to do that?

www.emtbforums.com

Thanks for the reply.
I'm not sure it's as simple as that. It works just fine when your peddling, then can drop to half speed, not necessarily off.
To me, it seems more likely to be a zero volts issue, or a fractured wire in the speed sensor cable. However, I've been really careful not move the suspension when free wheeling, to try and eliminate the wire moving.
Issues can manifest as a potential between the zero volt tappings on different voltage supplies from the battery.
Does anyone have a schematic of the battery connections?
I'm pretty sure it's a poor connection of the speed sensor into the motor housing, but if I'm dropping the motor to take a look, I may as well replace the sensor to be sure.
I'd just like to understand the exact problem....

 

[ichauchtt]

As said, I understand the problem, I had exactly the same, half speeds and then random when not pedaling, everything fine when pedaling. Eventually it ended in a W011 error. I thought it might have something to do with the flex and proximity between magnet and sensor which obviously changes when pedaling. I tried everything, from moving the sensor closer to put stronger magnets and all combination, nothing helped.
Eventually I changed the sensor and everything is fine since. I don't think it has anything to do with the voltage supply from the battery nor with the connection between sensor into the motor. Also my sensor itself looked perfect, I assume it is the cabling from sensor to motor, maybe poor insulation leading so some minor interferences.

 

[Josey Wales]

That's great information, many thanks.
I'll put my spare sensor in then, better to get it all done before this lockdown lifts next week and the bike park opens again!
I was thinking about putting a waterproof connector inline. As the cable leaves the frame. That way it's not a motor out issue everytime the sensor plays up.
This will be the second one, I think I broke the first one when I removed the shock to check the suspension travel when fitting a rear mudguard. It seems any stretch or excessive flex and the sensor plays up.
I have also tried other magnets, the current set up seems strange, why wouldn't the magnet travel over the centre of the reed switch? It barely sweeps one end. If I do put a connector inline, outside the frame, I may get a more robust reed switch and 3D print a holder for it. It's all a bit twee currently.