Pedal assist double hall sensor is intermittent

[M245]

Hello,

I've got a double hall pedal assist sensor (all in one unit) as shown in the photos.

There appears to be a gap between the left pedal arm and the sensor itself, which is causing intermittent power. I have tried to move it back and as close to the pedal arm as possible, but due to general riding, the vibration of the bike causes the sensor to move away from the pedal arm.

I don't think it's a defective sensor, as the power is produced when there is no gap between the sensor and the pedal arm, although this can be intermittent also.

I'm after some help and would ask if anyone can suggest a solution, as an alternative to buying a new sensor? I've been reading your forums and have found it very useful with some excellent advice.

Thanks in advance.

 

[Fordulike]

Is the crank arm torqued correctly to the spindle?

 

[M245]

Hi, thanks for responding. In all honesty, I don't know.
The arm itself seems tight with no movement.

The arm itself is attached with a single hex screw/bolt.
Inside is a square threaded bolt for the crank spindle itself.
I don't have a crank pulley tool for this so might need to get this looked at.
How would I check the torque and what would the torque be?

 

[Fordulike]

Only way of reliably torquing the bolt would be to use a torque wrench. Most people probably just use guesstimation when tightening, but I swear by one when tightening key bolts, such as the crank arm. It prevents smaller bolts from getting snapped off and helps stop bolts loosening over time. IIRC, my torque wrench only cost £25.

I torque my crank arm bolts to 40Nm, but it's best to check online first, to find out settings for your particular crank set.

 

[M245]

Thanks for this.

I'm a bit new to this, so forgive my sill question here.

Are you saying that torquing the outer bolt is what is required here?

It seems that this bolt is acting merely as a cover bolt. I took this bolt off and underneath, I could see the square type crank, which appears to be holding the pedal arm in place. When I removed the bolt, I tried to move the pedal arm, but it didn't give or move. It appears that the arm is being held by the crank pulley linked to the opposite/right arm.
Is this what you think needs torquing also?

 

[Fordulike]

Someone else can hopefully chip in on this, but I think the PAS sensor receiver is attached to the bottom bracket and doesn't move. The sensor disc is attached to the spindle and rotates as the pedal is turned. If the sensor disc isn't close enough to the receiver, then it will either provide an intermittent signal to the receiver, or not at all.

I'm mererly suggesting that tightening the crank arm, may move the disc closer, due to the spindle being tapered. The crank arm can feel secure, but due to the taper, may not be on tightly enough.

 

[Nealh]

I would say it needs tightening up, if it doesn't then you will have to put a shim in there to close the gap.

 

[Fordulike]

If you don't want to go to the expense of a torque wrench, then just use a hex key and hand power. That way you won't over tighten it, as your hand will hurt before that happens.

 

[M245]

To: Fordulike - I'm with you now. Thanks for the tips. I'll give it a go. Thanks again.

 

[M245]

Hi Nealh: What is a shim?

 

[Nealh]

A spacer though don't know if you can get ones for sq taper.
Wouldn't be hard to make one out of plastic and then put a sq hole in it.

 

[M245]

To Nealh: Ok. Thanks very much for this. I'll have a look at this and see if this works as well. Thanks again for your help.

 

[Woosh]

Someone else can hopefully chip in on this, but I think the PAS sensor receiver is attached to the bottom bracket and doesn't move. The sensor disc is attached to the spindle and rotates as the pedal is turned. If the sensor disc isn't close enough to the receiver, then it will either provide an intermittent signal to the receiver, or not at all.

I'm mererly suggesting that tightening the crank arm, may move the disc closer, due to the spindle being tapered. The crank arm can feel secure, but due to the taper, may not be on tightly enough.

you are correct. The teeth on the sensor shell key into the teeth of the bottom bracket left cup.

The main reason for mal-functioning is usually the rotor part of the sensor does not turn for one reason or another. A bit of grease would help the rotor to move more smoothly.
I would remove the left crank arm to examine the sensor.
Then turn the right crank slowly while watching the rotor of the sensor.
Make sure the whole thing work properly before re-installing the left crank arm.

This is the fixed part of the sensor. The rotor rotates over the brass washer.

 

[M245]

Hi Woosh. Thanks very much for this. I will need to buy a crank pulley so I can remove the left arm and take a look. I'll keep you all posted. Thanks again for your help and tips.

 

[M245]

Hello everyone.

I thought I would update you all since you all provided me with some useful advise. I'm sorry it's taken so long, but I had to buy a crank tool first before removing the left pedal crank arm and wanted to test the results properly.

It transpired that when I removed the pedal arm, a little piece of crumpled masking tape had fallen out. It appears that the person who fitted this (not me) used some marking tape as a seal to attach between the pedal arm spindle and the inner teeth rotating wheel of the sensor. When I put the sensor back onto the pedal spindle, I used a blunt instrument (i.e a pen) and tried to push the sensor around the pedal spindle by the teeth of the sensor.

The gentle force of the pen was enough to move the circular inner sensor wheel around the pedal spindle, without the pedal spindle moving.
There lay my problem.

So what I did was re-installed the sensor onto the spinal, but this time, instead of using marking tape, I used a thin rubber strip to gentle wedge between the sensor teeth and the square pedal spinal. I've tried to highlight this in the photo attached with a white circular (not very good) mark, which illustrates the rubber grip.

The area of the sensor marked with the letter's 'A' are fixed in place and do not move. It's just the inner circular teeth of the spindle that is supposed to grip the spindle and rotate when you pedal.

I have now had the chance to test this properly and rode 5 miles this morning with a constant source of pedal power being provided when needed. Whereas before, it was intermittent and in most cases, non-existent.

If I hadn't listened to any of you here, I would properly have not solved the issue. Thank you again to everyone that helped and gave some useful advice. I hope this is useful for others a like.

Thanks again.