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Speedo Sensor Fix

Discussion in 'CARC' started by GT-Rx®, Jul 23, 2009.

  1. GT-Rx®

    GT-Rx® Administrator Staff Member GT di Razza Pura

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    Repost by Steve B:
    Since several of us on the GuzziTech site seem to have fallen victim to the Speedo sensor gremlin (mostly on Grisos), I thought I'd have a crack at finding a longer-term solution. I've not written this as a specific 'How-to', though it'd be easy enough to replicate the process.

    To start with I've worked with the premise that the Hall effect sensor electronics are basically sound, more often than not (In my experience), failures of this type are a result of a process failure (Assembly). The store I bought the bike from was kind enough to let me experiment with a couple of defective sensors they'd amassed, plus a brand new replacement for my second failed unit. So I began looking at the body of the sensor under a microscope, probing where moisture might be getting in.

    [​IMG]

    Firstly the cable entry point seems (As several have said), a likely candidate and as you can see from the 2nd picture there is a gap into which water could pass through. What the shot doesn't show is there doesn't seem to be any form of protection in this area other than the glue/conformal coating around the wire sleeve exit on the inside of the sensor body. You would have thought they'd have filled the bore of the hole with something to seal it?

    [​IMG]

    [​IMG]

    Secondly the rubberized epoxy the manufacturers have used to cover/seal the PCB into the sensor case has not bonded sufficiently to prevent moisture ingress.
    As you can see from the following two shots I used a jeweler's screwdriver to test the bond between the two surfaces, could open a gap between the two materials with very little pressure applied. What I found disturbing with both test samples was that approximately a third of the overall circumference had not bonded the surfaces adequately. Viewing the gap under high magnification I found moisture droplets in-between the two surfaces, though they evaporated quickly under the warmth of the lights.

    [​IMG]

    Next I gently prized out the rubber epoxy, without damaging the PCB, was surprised at how cleanly it came away from the sensor case, without any tearing. As you'll see in the following pics, note the smooth internal walls of the sensor case (second pic below). This is what I suspect is the cause of all the trouble, the fact that the walls of the sensor case have NOT been scored to enable a good bonding surface.

    [​IMG]

    [​IMG]


    I debated whether to pull the PCB right out of the case, decided against it since the risk of damaging the circuit board/magnet/cable was quite high., bearing in mind the sensor is about the same size as a postage stamp. So at that point I decided to dry it out thoroughly in an environmental chamber @ 50C for 4 hours. I used a chamber rather than a conventional household oven, or a hairdryer simply to maintain a consistent temperature, to be pretty sure all of the moisture had been expelled.

    Applying the fix

    Since the walls of the sensor case were essentially smooth they needed a good roughing up to allow a good bond, so I broke out a needle file and scored the internal walls thoroughly, also lightly scoring around the entry point of the cable sleeve. I decided on a second application of conformal coating, since, on pulling out the rubber epoxy a small amount of the CC came away on its removal. I also wanted to make sure that there wouldn't be an air gap around the edge of the PCB and the case wall + sealed the internal end of the wire sleeve, since in theory moisture could travel (Internally), down to the sensor if the wire sleeve got damaged. Once that had been applied with a small artists brush, had let that dry I could now mix up and pour the two part epoxy I'd chosen.

    [​IMG]

    As you can see from the shot (Sorry I had to use my phone camera), having mixed up the two-part epoxy and poured it carefully into a syringe I could refill the sensors and lay a bead around the cable entry point.

    [​IMG]

    The only thing to make sure of when filling them up is to do it in a way that will NOT allow for any air-gaps, or spaces. Once full it was just a case of laying down a strip of double-sided sticky tape on a flat surface, pressing the sensor firmly to the tape and let the curing process begin. I could have put them in the oven again to speed the process, but according to the instructions would have invited some shrinkage in the mixture. So I let them dry out naturally for several days.

    [​IMG]

    You can see in the final shot the overall result.

    [​IMG]


    Results

    I've now fitted one of the sensors to the bike, have tested it in wet weather conditions, taken to the back roads for vibration tests and given the bike a good hosing down, during cleaning sessions and I'm happy to say no hint of a failure as yet.

    *Note* This article is the result of some experiments by the author, will not accept any liability for faults/accidents/wrath of deities, etc incurred by anyone else attempting this fix, i.e. If you mess it up... Don't blame me! :p
    I only say this as this is a public forum, we seem to sadly live in an age of litigation culture.
     
  2. guzziownr

    guzziownr Tuned and Synch'ed

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    Terrific article but I have one small critique. You start with the sensor off the bike!

    I was a little concerned about how difficult it would be to remove but Griso owner "Uncle" set me straight: All it takes is a 3mm T-handle.

    Roll the bike forward until you can see the sensor from the exhaust side:

    [​IMG]

    Get your T-handle snug and square. You don't want to strip them.

    [​IMG]

    Sensor is free, I used a dab of silicon where the wire goes into the sensor. If I have more problems I will get more serious.

    [​IMG]
     
  3. baloches

    baloches Cruisin' Guzzisti

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    Great work Todd!
    When you get down to analysing failures instead of just throwing parts at a problem, you make tremendous gains in reliability.
     
  4. Guzzi-Leif

    Guzzi-Leif Tuned and Synch'ed

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    What a superb help; thanks!
     
  5. bobra

    bobra Cruisin' Guzzisti

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    This is fantastic - thanks for taking the time to document. That's why this forum is one of my home pages!

    Cheers
     
  6. guzzi jon

    guzzi jon High Miler GT Contributor

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    Any so caler's that want the same process todd described, but done in a vaccuum chamber done, let me know. I could do a batch of 20 with the appropriate epoxy under a vacuum chamber which would suck the sealant into all the voids, and likely be even more reliable
    cheers
     
  7. Turtleman

    Turtleman Tuned and Synch'ed

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    I recently received a new speed sensor and was told that Guzzi have the improved the build of speed sensor and is supposed to be better in the wet.
     
  8. GT-Rx®

    GT-Rx® Administrator Staff Member GT di Razza Pura

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    Is it already on the bike? I'd be curious to see if the wire entrance and bottom look any different then the one at the top. If it's not mounted, can you snap a few photos to post?
     
  9. Mi_ka

    Mi_ka High Miler

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    Just saw this thread. Nice fix.
    If you ever have a completely removed sensor from its case please post a photo of the other side of the PCB.

    The center metallic piece is the magnet and in front of it (other side of the PCB) there should be attached a 3 pin flat transistor alike hall sensor (the 3 pins of which can be seen soldered at the bottom of the photo by the entrance of the cable).
    Other smd stuff suggest probably a 5 volt open collector output to GND type.
    If there is a close up of the hall sensor semiconductor itself we can lookup the numbers and see if it is a single or differential type sensor.
     
  10. pete roper

    pete roper GT Godfather!

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    As an addendum to this. My sensor on my pink Grisoin the US went out due to moisture and after it had dried out we dipped it in a big can of an aerospace dialectric varnish called Glyptol I believe that Jon had a big can of at home due to it having gone past its use by date.(They are very anal about such things in aerospace and Jon says it is cheaper to get a new can rather than re-certify it after a year.) This stuff IS expensive, about $300 a can apparently but it worked splendidly sealing the unit completely with just a dipping. Alowed it to dry overnight and bob's yer uncle!!!!

    Pete
     
  11. GuzziHero

    GuzziHero Cruisin' Guzzisti GT Contributor

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    My replacement that I sprayed with acrylic lacquer is still working with no problems.
     
  12. Griso Guy

    Griso Guy Cruisin' Guzzisti

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    The Epixy Resin, what make & where can one buy it?
    Thanks
    Doug
     
  13. jiltedjohn

    jiltedjohn Cruisin' Guzzisti

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    Araldite from a hardware store might do it
     
  14. GT-Rx®

    GT-Rx® Administrator Staff Member GT di Razza Pura

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    Seems the most important part to waterproof is where the wires enter the sensor. I've done several in place, with no issues to date.
     
  15. rustyrotor

    rustyrotor Tuned and Synch'ed

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    I remember being told that this part had been redesigned?
    True?

    Not academic, my third (!) one is shot and needs replacing so I need to know if I have to
    waterproof it prior to installing.

    And one of the allen heads is stripped. Yay.
     
  16. jiltedjohn

    jiltedjohn Cruisin' Guzzisti

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    Have run mine through some torrential downpours with no trouble , having used just a bit of general purpose clear silicone
     
  17. Calijackalbob

    Calijackalbob Cruisin' Guzzisti

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    Not so simple a job to remove the speed sensor on a Bellgio, cant get to it with the wheel on because the exhaust is in the way. Anyway, just replaced mine (Or my mechanic did.) He had to remove the exhaust and the back wheel to get to it. He coated the wiring and the sensor with silocone to prevent problems. ) Speedo working reliably now in torrential Monsoon rains. Unfortunately, it seems that while removing the exhaust mufflers, he put too much strain on one and a crack has opened up in the muffer where the fixed/welded in nut is, that holds the pipe to the bracket.

    Hate that!

    But on a brighter note,.......................

    Ain't she goregeous?
    [​IMG]
     
    Garrett Fulton and kampe like this.
  18. Nordicnorm

    Nordicnorm Cruisin' Guzzisti GT Contributor

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    What was the original problem? Picking up an '07 Griso next week. Bouncing numbers all over the place at low speed, then stable when you get going. Fairly high mileage. Lots of rain up here in the NW. The selling dealer is investigating before I go get it. This is most likely the issue I suspect, so if he does not find anything unusual (he is good), I'll look into this.
    One more for the bucket list....and maybe time for a new avatar
     

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