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What would cause the driven gear on the VSS to slip?

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    #1

    What would cause the driven gear on the VSS to slip?

    So I discovered what the problem with my VSS in the 93 vic is... either the driven gear is binding up on the VSS itself, or the output shaft teeth are not engaging it very well... either way, it's slipping and not actually being spun properly (lack of teeth engagement). What would cause this? Is this an indicator that my output shaft is loose on the transmission? (it is the original AODE, but it was rebuilt at 120K, though it has over 220K on it). That would explain a lot of the issues with the car actually.

    The way I found out was I spun the tires a little taking off from a light and as the car moved on down the road, it took a while for the speedo to tick up to the speed I was actually going.

    Only two things are infinite, the universe and human stupidity, and I'm not sure about the former. -- Albert Einstein
    rides: 93 Crown Vic LX (The Red Velvet Cake), 2000 Crown Vic base model (Sandy), 2003 Expedition (the vacation beast)
    Originally posted by gadget73
    ... and it should all work like magic and unicorns and stuff.
    Originally posted by dmccaig
    Overhead, some poor bastards are flying in airplanes.
    Tags: None
    #2
    The shaft of the VSS is square, and it sits into a square hole in the plastic gear. If the gear has rounded out or if the teeth are worn down it might skip. The output shaft on the trans I don't really expect can move much without you knowing it. The drive teeth are cut directly into the output shaft, and for that to move enough to not engage the plastic gear you'd probably have some pretty serious problems going on back there.


    Its also possible that the speedo itself is flukey. I rebuilt one for John that had a stuck movement. Its basically a motor that doesn't get a moving field. There are two coils in there and the speedo needle itself is fixed to a piece of iron. As the voltages shift on those two coils, it pulls the iron vane in accordance with the shifting field. If that moving piece doesn't move smoothly, it'll make the speedo respond improperly.
    86 Lincoln Town Car (Galactica).
    5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

    91 Lincoln Mark VII LSC grandpa spec white and cranberry

    1984 Lincoln Continental TurboDiesel - rolls coal

    Originally posted by phayzer5
    I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

    Comment

      #3
      I do believe that I have read somewhere that the teeth on the driven gear can wear over time, especially with the higher tooth-count gears.
      Vic

      ~ 1989 MGM LS Colony Park - Large Marge
      ~ 1998 MGM LS - new DD
      ~ 1991 MGM LS "The Scab"
      ~ 1991 MGM GS "The Ice Car"

      Comment

        #4
        I'm using an autometer digital speedo in the 93 now, so that's not it. But considering that I haven't checked the center bore on with of the gears I'm using, that might be it. Neither of the plastic gears are showing any real wear on the teeth.

        Only two things are infinite, the universe and human stupidity, and I'm not sure about the former. -- Albert Einstein
        rides: 93 Crown Vic LX (The Red Velvet Cake), 2000 Crown Vic base model (Sandy), 2003 Expedition (the vacation beast)
        Originally posted by gadget73
        ... and it should all work like magic and unicorns and stuff.
        Originally posted by dmccaig
        Overhead, some poor bastards are flying in airplanes.

        Comment

          #5
          Ok, the teeth have been checked on the driven gear, then like gadget said if it's not a faulty speedo head the square end on the on the VSS could round out the square hole it sits in.
          I would also second what was said of the drive gear and output shaft not being the likely problem otherwise I would expect bigger problems to be present if there was an issue there.
          Vic

          ~ 1989 MGM LS Colony Park - Large Marge
          ~ 1998 MGM LS - new DD
          ~ 1991 MGM LS "The Scab"
          ~ 1991 MGM GS "The Ice Car"

          Comment

            #6
            Good to know. Kinda a pisser if it is the square hole rounded out since that gear is only 2 years old. I can believe it with the gear that was originally in it as it has over 200K on it... but this purple one has less than 20K on it.

            Only two things are infinite, the universe and human stupidity, and I'm not sure about the former. -- Albert Einstein
            rides: 93 Crown Vic LX (The Red Velvet Cake), 2000 Crown Vic base model (Sandy), 2003 Expedition (the vacation beast)
            Originally posted by gadget73
            ... and it should all work like magic and unicorns and stuff.
            Originally posted by dmccaig
            Overhead, some poor bastards are flying in airplanes.

            Comment

              #7
              On my recent conversion to the 2000 P71 cluster in my 91 MGM I had a condition on the first test drive where the speedometer did not move smoothly. I spun my tires in the snow and with the stock speedo I had previously observed that it would smoothly run up to 50-60MPH but with the new speedo it would jump up to 30MPH very suddenly after not moving then sit there for a second and maybe jump more if I kept on the gas. On deceleration it would stick before jumping back down. What I found is that the speedo needed to be pushed in more, the leads were not all making good contact. After I made sure the speedo leads were all completely seated it worked just as smooth as the stock unit. I thought it was pushed all the way in before the test drive but apparently it wasn't.
              Vic

              ~ 1989 MGM LS Colony Park - Large Marge
              ~ 1998 MGM LS - new DD
              ~ 1991 MGM LS "The Scab"
              ~ 1991 MGM GS "The Ice Car"

              Comment

                #8
                As already stated, I don't have a stock speedometer. It's not a needle type, it's a digital number type from AutoMeter. All wires are soldered and I've detected no issues with the VSS signal other than it not matching up to the pulses that the output shaft sensor is providing. The only thing remaining is the square shaft issue or poor tooth engagement.

                When I spin the tires, the speedo typically goes up to whatever speed I'm spinning at and then drops instantly to the speed I'm doing when I gain traction. This complete lag is new.

                Only two things are infinite, the universe and human stupidity, and I'm not sure about the former. -- Albert Einstein
                rides: 93 Crown Vic LX (The Red Velvet Cake), 2000 Crown Vic base model (Sandy), 2003 Expedition (the vacation beast)
                Originally posted by gadget73
                ... and it should all work like magic and unicorns and stuff.
                Originally posted by dmccaig
                Overhead, some poor bastards are flying in airplanes.

                Comment

                  #9
                  I wonder if it may be a sample rate thing with the Autometer specifically. If the input changed faster than it can respond it might act up. Still though, I'd expect it to be fast enough to not be obvious that it was not responding.
                  86 Lincoln Town Car (Galactica).
                  5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

                  91 Lincoln Mark VII LSC grandpa spec white and cranberry

                  1984 Lincoln Continental TurboDiesel - rolls coal

                  Originally posted by phayzer5
                  I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

                  Comment

                    #10
                    yeah... it used to go up quicker than that... so I think that's the issue with the VSS. Either the plastic gear and clip are binding somehow on the VSS and refusing to turn, or like you said, the center square drive is not as tight as it needs to be. Gonna be a while before I get another chance to check that out though.

                    Only two things are infinite, the universe and human stupidity, and I'm not sure about the former. -- Albert Einstein
                    rides: 93 Crown Vic LX (The Red Velvet Cake), 2000 Crown Vic base model (Sandy), 2003 Expedition (the vacation beast)
                    Originally posted by gadget73
                    ... and it should all work like magic and unicorns and stuff.
                    Originally posted by dmccaig
                    Overhead, some poor bastards are flying in airplanes.

                    Comment

                      #11
                      I guess its also possible the VSS is dying too, but there isn't much in there to fail either. You could put it on a scope and spin it. it makes a nice fat triangle wave at a couple volts peak to peak.
                      86 Lincoln Town Car (Galactica).
                      5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

                      91 Lincoln Mark VII LSC grandpa spec white and cranberry

                      1984 Lincoln Continental TurboDiesel - rolls coal

                      Originally posted by phayzer5
                      I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

                      Comment

                        #12
                        Both VSSs I have are acting like that though. If it's still a ghost issue after I check the square drive, I'll just leave it.

                        Only two things are infinite, the universe and human stupidity, and I'm not sure about the former. -- Albert Einstein
                        rides: 93 Crown Vic LX (The Red Velvet Cake), 2000 Crown Vic base model (Sandy), 2003 Expedition (the vacation beast)
                        Originally posted by gadget73
                        ... and it should all work like magic and unicorns and stuff.
                        Originally posted by dmccaig
                        Overhead, some poor bastards are flying in airplanes.

                        Comment

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