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1973 SM465 Neutral Saftey/Backup question

Discussion in 'The Garage' started by 73k5blazer, Jan 27, 2005.

  1. 73k5blazer

    73k5blazer Unplug the matrix cable from the back of your head Premium Member

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    So I'm in the middle of my rebuid project, I have a SM465 transmission.
    I thought I knew what I had, but I guess I'm wrong, on my trans there is two connectors, 1 one wire(top of case angled 45degrees to driver side), 1 a two-spade terminal (top of case, lower than the other, pointed straight sideways to driver).
    My first guess is ok, on'e s neutral safety switch and the other is backup.
    One is definatly the reverse light switch the two-spade lower one pointed directly to the drivers side. Hooking the ohm meter to it, it goes from infinite to 0 when I put it in reverse. Ok, great. THe other I cannot seem to make it do anything in neutral or anything else. I removed it and tried to actuate the little ball while it was on a meter, nothing. I tried running power though it, ohm testing it..nothing makes it do anything.
    So either my switch is bad, or I'm not running the right test.
    Anyone know what this switch is supposed to be for?
    As I said, before I dissabemble the truck, I'm almost sure my truck had no neutral switch, well it may have been there, but it sure wasn't hooked to anything because I'm sure I could start my struck in any gear, I remember running out of gas 30 yards from a gas pump once and cycling the starter while in gear to get there...
    So what is this switch?
     
  2. 73k5blazer

    73k5blazer Unplug the matrix cable from the back of your head Premium Member

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    OK, now I'm really confused. I viewed the hole where the switch scews into, and it has a piece of metal covering it in all places, exept third gear. So what gives here? It turns out I can bench test the switch, the gear oil was getting in the way before. When I completely dried the thing, it is the most simplist switch ever. A metal body with a spring loaded ball that pushes against the body. When you push the ball in, infinite resistance, otherwise when the ball is pushed out by the spring to contact the edge of the body of the switch, you have 0 resistance.
    Ok, so looking at the hole in my transmission where this thing goes, it would always produce infinite resistance, except in third gear. Which after I cleaned it , reinstalled it, I confirmed. Infinite resistance, until I put it in third gear ,then I have 0 or almost 0.
    :confused::confused::confused:
    I'm very confused, mabey I've had 1 too many beers today while "working from home"
     
  3. diesel4me

    diesel4me 1 ton status Premium Member

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    transmission controlled spark

    If your truck is a 73,that switch is probably a "transmission controlled spark" switch,they had a solenoid in the vacuum advance hose that would shut the vacuum off the the vacuum advance in high gear for lower emissions,controlled by that switch--I've only seen this setup on automatics,but maybe they had them on the manual tranny's too..:confused:
     
  4. dyeager535

    dyeager535 1 ton status Premium Member

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    Yes, emissions related to spark.

    I've got one in my garage like that.

    The one that comes out parallel with the ground is the backup light switch, all you need to worry about.
     
  5. Blazer1970

    Blazer1970 1/2 ton status

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    Yes, switch is for TCS and as you have found it indicates that the tranny is in 4th gear.
     
  6. 73k5blazer

    73k5blazer Unplug the matrix cable from the back of your head Premium Member

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    Alrighty, that makes sense, Yeah I meant 4th gear, not third, sometimes I forget to count the granny low as 1st.
    Thanks for the help!
     
  7. R72K5

    R72K5 Banned

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    granny or not, it is 1st no matter which way anyone says or thinks, its just super deep ratio

    early 70s had that TCS system, IE the second switch

    good luck
     

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