Using diff "vss" as an engine vss sensor, is it possible?

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    Originally posted by RunningProblem View Post
    Did you ever get this figured out? The Sterling 10.25 I have has the same tone ring and plug so I'm curious to know if it could be use for a speedometer in place of the VSS in the transfer case. MY gut says it would if I found a programmer like LT1Swap who was familiar with the Ford rear axle and what the output voltage is.
    The below reply does answer some of my questions.

    If I were doing an LS type swap where I could use HP tuner, this would be a trivial solution. They offer a method to convert pulses in to correct "range".

    I'm not sure I've heard of an easy method to convert a signal with a TBI computer.

    Originally posted by Swampee View Post
    In theory the axle ring could be used. Find the tooth count that makes the engine happy and do the math on the gear ratio to make the appropriate tooth count. The ring is removable so have one cut out that is similar thickness and OD to have the appropriate tooth count.
    there are variables that need attention. Is the gm speed sensor 2 wire or 3? The ford sensor is normally 2 wire. Theres a possibility that you could mount a different sensor in the hole with some ingenuity if the gm is 3 wire.

    Think outside the box and decide if the gain is worth the work.
    If the ring is removable, what is different in the diff? Are the gears a different thickness? Or is the carrier different?

    It has been many years since I played with a "TBI" VSS... but the LS ones are 2 wire.


      The only thing different in the diff would be the tooth count. Say you have 4.10 gears. The factory vss reads X number of teeth I'm not sure but we will call it 10 teeth for easy numbers. The driveshaft rotates 4.1 times for every single rotation of the axle. So you would need more teeth on the axle ring than the case output.
      If the factory gm is 2 wire then I see no issues there. I was just planning for potential hiccups in the system.
      so find the stock gm tone ring count and count the axle ring with the gear ratio in mind and figure out how many teeth you need to make the tbi enjoy what's going on.

      Maybe you get really lucky and it's a divisible number based on the two and only have to pull the carrier and grind off every other tooth or something similar. This will all depend on the numbers.
      Do a little homework and report back.
      1- gm tooth count for VSS
      2- ford ring tooth count
      3- gear ratio you will run


        Use pulses per mile as the common denominator. That's what the computer wants to know, it doesn't care if you use the trans, tcase, rear diff, or glue a magnet to a tire.

        I vaguely remember that the F350 PSOM wants to see 8000/mi.

        The 10.25 tone ring presses (taps on w a deadblow) on the OD of the carrier, with a tab to prevent slipping. Waterjet or lasering a ring to replace it would be pretty easy, as long as you're precise- clearance to the pickup is important (FSB link above talks about .1mm/.004" location accuracy). Also, note the offset- it's not a flat plate, it has a rib on the upper face in the photo so that the teeth are stepped away from the ring gear.

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