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Refurbishment of a pawl unit - these get very little notice or attention

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  • Refurbishment of a pawl unit - these get very little notice or attention

    Refurbishment of a pawl unit - these get very little notice or attention

    On rebuild of DDG I had to deal with a Pawl/Cancel unit that seemd to be intermittently "shorted" and the actual pawl was sticky.

    The sticky part was as suspected, dried up lubricant, so the body was duly taken apart, cleaned out and lightly smeared with grease and then a drop of oil. Do not fire loads of grease in there.

    The floating contact was cleaned up and floats on 3 springs, watch and not drop / lose one like I did as I was very lucky to have a busted spare to borrow from.

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    The "short" ended up being where it seemed to have been arcing on switch, so I had to carve out that trough, is suspect worn copper plus grease left it part conductive, explains why the original hold on coil looked like it had been in a microwave

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    The wires were also cleaned off the ends and tinned again, soldered to the contacts with new material and then filed flat not to foul the contacts.

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    Click image for larger version  Name:	20200624_142220.jpg Views:	3 Size:	34.9 KB ID:	9171

    Thats it, nothing complex, dont use rough material to clean the copper, ususally if you clean off the material and use a pencil eraser it is sufficient to clean up the copper very well.




    Last edited by John A. Ross; 24 June 2020, 08:27 PM.
    / John

  • #2
    top job

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    • #3
      Cheers Dave

      No mods though !

      I will need to think something up as this is all "same old" just took note of it as indicators not cancelling is a common comment from peeps

      Other than broken ground for the hold on coil I reckon this collection of conductive material build up is what caused the coil to self destruct.

      One to watch as I reckon no one EVER cleans this
      / John

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      • #4
        Hi John, Dave LL is a Mk.1 so has never had the driver-bush needed to supply the intentional "lost-motion" to operate the later pawl-unit. (This was devised to get over the problem of the steering going more than +/- one full turn for full lock.) I keep looking for a spare column to play with, but none have dropped out of the woodwork yet! My thinking has been to go for a magnetic sensor and "count" the extra pass, but as an interim measure (over a decade ago!) I made a simple time-out device. This has worked fairly well, but in its original and present form, it demands about 4 V drop. The only "fail to latch" incidents from this have proven to be due to the mountings of the indicator-switch working loose - one nut is easily tightened in-situ but the other is.... I think I've figured how to get most of the dropped volts back, so will make a modified duplicate, which is promised to Dave. The Gold Standard of course would be the magnetic-cancel... needs one magnet and two sensors. FWIW My timeout was designed for about 12 seconds; this served me very well for many years but in modern traffic condiitions I think it now needs to be longer - say 20 seconds or even more!

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        • #5
          Gary

          We have used these and they are really nice, they take a punding as well. Unfortunately I cannot disclose where used due to security restrictions but let us just say they take a punding in a very unfriendly enviroment, sensors, movings bits, solenoids.....

          https://standexelectronics.com/produ...s-reed-sensor/

          Directivity can be "focussed" by use of a ferrous metal shield, same way as halls but these are reed based so no vague transition area, just on/off

          Always thought the pawl unit worked just fine
          / John

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          • #6
            It has meanwhile occurred to me, that a single inductive pickup can "know" the direction when the magnet passes it. FWIW I had a LOT to do with reed-switches c.1980 but never warmed to them...

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