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Thread: 40 tooth vss sensor gap/clearance

  1. #1
    Fuel Injected! JeepsAndGuns's Avatar
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    40 tooth vss sensor gap/clearance

    So just a tiny back story to explain what I am doing.
    I am going to be building up my 79 cherokee. Its getting dana 60's, NV4500, and a NP205. The Np205 I am using is out of a ford. The ford speedo cable has the gear made onto the end of it. My cherokee uses a regular thread on GM style speedo cable output in the t-case. I originally modded a chevy NP205 tailhousing to get the gm speedo drive. I did this many years ago when I rebuilt the NP205. Its been setting in storage waiting for me to get everything else built. So at the time I modded the chevy tailhousing, I was planning on keeping the stock speedo.
    Fast forward to now and I have since joined the world of fuel injection. I have also decided to ditch the stock guages (since the speedo is the only original one left working and all others have been replaced with the small cheap aftermarket ones) I figured, since I am running a vss for the fuel injection, why not switch to a electric speedo. I have found some I really like, and can use many different vss signals. (www.speedhut.com) At first I figured I could just reuse the vss I am using now, since it will thread onto the modded chevy tailhousing for the NP205. However I will have no way to adjust for the large change in tire size and gear ratio. Currently the speedo and speed displayed in the ecm data logs reads correct But I know they wont once I complete the build (currecntly 31's and 3.54's, but will change to 35's and 5.13 gears)
    But then I got poking around google and found where people have put a NP241 40 tooth wheel and sensor into the NP205 tailhousing. Simply machine a flat onto the tailhousing, drill and tap for the sensor, then trim down the length of the tone wheel and it slips right on the NP205 output shaft in place of the original speedo drive gear. I can do this to the original ford tailhousing and sell the gm one. Then I can simply use a DRAC module, mod it for my tire size/gears and then use it for the ecm and the speedo. Having the drac and being able to install different jumpers in it would be a great plus for me as I have several parameters set that are speed specific. The speedo is programable to use about any ppm, but I would prefer the ecm vss signal to pretty close to correct, hence why I want to do this mod.
    I can do the machine work with my mill and lathe no problem. I have sourced a tone wheel and sensor from my local pull a part. But what I can not figure out is the gap between the tone wheel and the sensor. This will determine how much I machine off the tailhousing where I mill it flat. All the writeups i saw, none mention the gap. I'm sure there is a narrow range. Too far away and it wont read or read wrong. Not sure what would happen (if anything?) if it was too close (but not touching)
    So does anyone know what the gap should be? Is there even a spec? The tone wheel and speed sensor is from a 94 or 95 truck. Rockauto shows the sensor as fitting 88-99 models.
    79 Jeep Cherokee, AMC 401, T-18 manual trans, hydroboost, 16197427 MPFI system---the toy

    93 Jeep YJ Wrangler, 4.0L, 5 speed, 8.8 rear, homebrew hub conversion and big brakes, hydroboost, 2.5in OME lift, 31x10.50's---the daily driver

    99 Jeep WJ Grand Cherokee limited, 4.0L, auto, 2wd, leather and power everything, 99% stock---the long distance highway ride.

  2. #2
    Super Moderator Six_Shooter's Avatar
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    Why can't you change the VSS divisor to set the read speed to be correct?
    The man who says something is impossible, is usually interrupted by the man doing it.

  3. #3
    Fuel Injected! JeepsAndGuns's Avatar
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    Possiably. But I still need to know the gap between the sensor and the wheel.
    Should I just set it as close as I can without it rubbing? Or can it be too close?
    79 Jeep Cherokee, AMC 401, T-18 manual trans, hydroboost, 16197427 MPFI system---the toy

    93 Jeep YJ Wrangler, 4.0L, 5 speed, 8.8 rear, homebrew hub conversion and big brakes, hydroboost, 2.5in OME lift, 31x10.50's---the daily driver

    99 Jeep WJ Grand Cherokee limited, 4.0L, auto, 2wd, leather and power everything, 99% stock---the long distance highway ride.

  4. #4
    Fuel Injected!
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    0.010"seems to be a very common value. I have a plastic 0.010 feeler gauge for this purpose.

  5. #5
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    Might be larger... .020". Hard to find confirming information right now.

  6. #6
    Fuel Injected! JeepsAndGuns's Avatar
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    I did some more in depth google searching and found very little. I found two values. One place said .030, and another said .028.
    79 Jeep Cherokee, AMC 401, T-18 manual trans, hydroboost, 16197427 MPFI system---the toy

    93 Jeep YJ Wrangler, 4.0L, 5 speed, 8.8 rear, homebrew hub conversion and big brakes, hydroboost, 2.5in OME lift, 31x10.50's---the daily driver

    99 Jeep WJ Grand Cherokee limited, 4.0L, auto, 2wd, leather and power everything, 99% stock---the long distance highway ride.

  7. #7
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    I saw that .028" post.

    Still don't have time to dig through GM literature.


    This looks promising:
    http://www.advanceadapters.com/downloads/50-9305.pdf
    Step 6 P.1 says .010 - .012

    Another Advance Adapters:
    http://atlas-tc.com/pdf/50/50-0403.pdf
    P.1 says .009 - .013

    Plus we've got mechanicman's experience... I'd probably go with .010"

  8. #8
    Fuel Injected! JeepsAndGuns's Avatar
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    Good catch. I would have never thought to check advance adapters.
    OK, I'm gonna shoot for .010.
    Thanks.
    79 Jeep Cherokee, AMC 401, T-18 manual trans, hydroboost, 16197427 MPFI system---the toy

    93 Jeep YJ Wrangler, 4.0L, 5 speed, 8.8 rear, homebrew hub conversion and big brakes, hydroboost, 2.5in OME lift, 31x10.50's---the daily driver

    99 Jeep WJ Grand Cherokee limited, 4.0L, auto, 2wd, leather and power everything, 99% stock---the long distance highway ride.

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