Author Topic: How to repair your ShiftAssist  (Read 1406 times)

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Offline MachWun

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How to repair your ShiftAssist
on: January 21, 2021, 08:43:28 PM
Ok, lots of questions on flakey quickshifters, and I have the solution. 

First, it's basic operation.  The quickshifter is a Variable Reluctance Sensor.  It has a variable output, based on the sensed magnetic field.  It has 3 wires.  Power, ground, and signal.  The black plastic portion of the quickshifter is a loop of wire.  The loop encircles the rod that extends out of the rear of the quickshifter.  As that rod moves in and out of the sensor loop, its output voltage varies.  At rest, it produces a 4.5 volt signal.  As the quickshifter is extended, the output signal drops to .5 volts.  The rate of signal voltage dropping is directly proportional to the rate of shifter actuation.  If you bang the shifter, you'll see if go from 4.5 to .5 very fast.  If you pussy-foot it, there will be a much longer delay.

The extension rod that comes out of the back of the QS is magnetized in a VERY special way.  It must be 'clocked' inside the black plastic loop at exactly the correct position.  If it is not clocked in the correct position, the transition from 4.5v to .5v will not be smooth.  There will be peaks and valleys, which I will call hash from here on.

This hash is why your QS is not working.  The DME sees this hash, and can't determine the position of the QS.  Your QS might work for a few minutes, then quit until you restart the bike.

The goal is to find the clocked position of that extension rod, that produces ZERO hash.  You will need to loosen both heim joints from the QS assembly.  The rear heim is loctited to the extension rod.  You must loosen this very carefully. 

The downside is to fix this, you will need a labscope, or oscilloscope.  Hook it up to the ground, and signal wires as shown in the video.  Actuate the QS, and watch the waveform. If you see hash, rotate the extension rod till it's gone.  Does not matter which direction you go.  Just twist it slowly till you get a smooth waveform.  You will then need to rotate the heims so that they are perfectly vertical...WHILE NOT TURNING THE EXTENSION ROD.

Below is a basic video.  Excuse the audio, I was jamming out while I got my QS working again.

https://photos.app.goo.gl/VbdMnFHZgwieoYNd6

Once you get the extension rod in the correct position, clear the adaptions for the transmission, and go for a ride!

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Offline rogracer

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Re: How to repair your ShiftAssist
Reply #1 on: January 22, 2021, 10:13:06 PM
Good Stuff  :152: :047: I always thought the quickshifter was a load cell that responded to applied force.  But you're saying it responds to a bit of axial movement. That seems a bit sloppy to me...like there is a bit of free-play between the shift-lever and transmission (which I've never noticed!)  Is the shaft spring-loaded to minimize this and maintain the zero-position?
Last Edit: January 22, 2021, 10:13:41 PM by rogracer

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Offline rogracer

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Re: How to repair your ShiftAssist
Reply #2 on: January 25, 2021, 04:10:01 PM
So I futzed around a bit with my QS this morning and I don't see this axial movement that you speak of.  It seems pretty stiff and solid without really any free-play  :084:

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Offline MachWun

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Re: How to repair your ShiftAssist
Reply #3 on: January 25, 2021, 04:33:13 PM
*Originally Posted by rogracer [+]
So I futzed around a bit with my QS this morning and I don't see this axial movement that you speak of.  It seems pretty stiff and solid without really any free-play  :084:

The rear heim joint...It's currently locked to the extension shaft.  So twist the heim in relation to the body of the sensor...Also, this is useless without a scoped hooked up and you can see the waveform.

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Offline rogracer

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Re: How to repair your ShiftAssist
Reply #4 on: January 25, 2021, 05:02:51 PM
I got you...but just trying to understand what you meant by "As that rod moves in and out of the sensor loop..."
That seems to imply axial movement of the shift-rod.

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Offline MachWun

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Re: How to repair your ShiftAssist
Reply #5 on: January 26, 2021, 02:16:41 PM
The rod the rear heim joint is attached to, extends about an additional half inch when you load up the quick shifter.  Sit on the bike and actuate the shifter while you're looking at it.  It's near impossible to extend by hand unless you really are cracking on it.

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Offline rogracer

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Re: How to repair your ShiftAssist
Reply #6 on: February 07, 2021, 05:25:19 PM
Right you are MachWun  :152:  I went out again and did indeed observe the movement you described.   There appears to be an internal preloaded spring that prevents relative movement up to a certain level of applied force, at which point the shaft moves relative to the housing.  Since it is this movement that generates the signal, it would seem to imply that the quickshifter will not work unless your foot applies enough force to overcome the preload.   I'm shocked at myself for having never noticed this  :027:

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Offline MachWun

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Re: How to repair your ShiftAssist
Reply #7 on: February 07, 2021, 06:07:30 PM
*Originally Posted by rogracer [+]
Right you are MachWun  :152:  I went out again and did indeed observe the movement you described.   There appears to be an internal preloaded spring that prevents relative movement up to a certain level of applied force, at which point the shaft moves relative to the housing.  Since it is this movement that generates the signal, it would seem to imply that the quickshifter will not work unless your foot applies enough force to overcome the preload.   I'm shocked at myself for having never noticed this  :027:

It is indeed a strange system, and I believe the spring pre-load is why they call it Shift Assist, and not a quick shifter.  It is actually the spring pressure that changes the gear, not your foot.  You load up that spring with your foot.  At full compression, the bike sees the .5v signal, and cuts spark and fuel.  At that point, the spring releases it's energy and clicks the shifter for you.

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Offline MA413

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Re: How to repair your ShiftAssist
Reply #8 on: February 07, 2021, 08:04:46 PM
Nice work. I learned something new about our bikes and that  Iím not the only person that still rocks ODB :008:
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Offline rogracer

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Re: How to repair your ShiftAssist
Reply #9 on: February 08, 2021, 10:23:20 PM
MA413-  You have a MY 2017, so you have an up-and-down quickshifter.  We were talking about the up-shift only QS on the MY 2015 and 16.....the shaft only extends against the spring preload when upshifting. On downshifts, the shaft and housing are essentially locked together.  I'm curious on your MY 2017 if BMW is still using a spring-loaded mechanism (modified so the shaft moves relative to the housing in both directions), or if they went to a load cell.  :084:

 



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