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355 My computer won’t remember seat positions

Discussion in '348/355' started by cyberdoc, Jul 23, 2019.

  1. cyberdoc

    cyberdoc Rookie

    Nov 21, 2013
    1
    Chicago area
    Full Name:
    Michael Verta
    My 1997 355 had a convertible top that wouldn’t go down. Replaced the hydraulic hoses, both seat potentiometers, and the elastic bands. Got the top working and “taught” the computer the seat positions. Worked exactly twice. Now the dealer has it and can’t figure out why after several up and downs, the computer seems to forget the seat positions. Anybody else ever heard of this? BTW the battery is brand new and everything else works fine.
     
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  3. Qavion

    Qavion F1 Rookie
    Silver Subscribed

    Feb 20, 2015
    4,867
    Sydney
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    Ian Riddell
    Where did you find seat potentiometers? Were they second hand or old new stock? Were they checked internally prior to fitment?

    A gentleman on a Jaguar forum is working on a 3D-printed replacement part for the potentiometers. They share the same easily broken "claw drive". He had trouble with the first batch. The claw material is softer than the original and the additional thickness of the claw fingers made it difficult to install the retaining ring without breaking the fingers. He's working on a installation tool. An o-ring can be used instead of the steel retaining ring, but it has to be a particular size and hardness. I'll let the forum know if we have success. My local independent has a few potentiometers on which I can experiment.

    I can't say I've heard of a computer causing this problem before. It's probably the potentiometers. Perhaps it's possible to somehow tweak the SD calibration?
     
  4. Challenge

    Challenge Formula 3

    Sep 27, 2002
    1,534
    PA
    Full Name:
    Kevin
    Ian knows his stuff. I would suspect your pots are broken internally, or at least the tiny plastic claw inside them are no longer making good contact with the ball that drives the rheostat gear. This 'can' be a free fix by super glueing the claw back to the ball gear inside the potentiometer. I have fixed both of mine permanently with this method. It just takes time and patience.
     
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  5. Qavion

    Qavion F1 Rookie
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    Feb 20, 2015
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    Ian Riddell
    The potentiometer has a sliding contact which is almost like needle on an old fashioned record player (if you're old enough to remember these) and pushes very heavily on the resistive track. The ball and socket (claw) drive on the potentiometer has to fight this resistance. If the claw is still intact, it may help in some cases to lubricate the track with an appropriate lubricant. One of the first version 3D printed claws with an o-ring fitted instead of metal clip worked on one potentiometer, but not on another (purely because of the tension of the needle)
     
  6. greybeast

    greybeast Formula Junior

    Nov 15, 2011
    251
    Long Island
    You can repair a seat potentiometer with no retaining clip. See my thread. The pics are out of order but if you read the instructions, it refers to the pics as necessary. Top has been working perfectly for more than 6 years.

    It is important to make sure you set the resistance values to the right number otherwise the ECU will not "know" where the seat is. For example, if you reinstall the seat in the full aft position, the resistance value should read the correct kOhms for that position.

    https://www.ferrarichat.com/forum/threads/seat-potentiometer-repair-no-glue-pics.400259/
     
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  8. Qavion

    Qavion F1 Rookie
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    Feb 20, 2015
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    Very important. I see your fix doesn't allow for the required slippage at the endstops during calibration. That's the reason there is a ball and socket.

    Many ways to skin a cat ;)

    I see someone used a soldering iron to create new grooves for the metal clip higher up on the "claw" after the fingers had broken.
    Also, someone cut off all the fingers and put a small piece of clear plastic fuel pipe over the claw and ball. Simple, but I don't know how long it would last. I guess thermfit would work too, but you would have to experiment with "grip".
    Someone also stuck a nail in the centre of the claw and the ball. The slippage was based on the size of the hole.
     
  9. greybeast

    greybeast Formula Junior

    Nov 15, 2011
    251
    Long Island
    Yes. I did the calibration with everything disassembled. The seat was set fully aft and i manually spun the pot gear until it read the proper “aft” resistance, then same for forward. Since it was reassembled 6 years ago it hasn’t required any further attention.
     

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