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Thread: 95 TBI into older 4x4 vss question

  1. #1
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    95 TBI into older 4x4 vss question

    Hello, newbie here but I did my introduction post in the appropriate forum. Plus I recognize a few names.

    So, I joined to ask about some help installing a 95 LO5/4l60e into a 72 4x4. I got alldata for my wiring(or most). But what I need help with is the vss. Ive searched and cant find a definite answer on how many ppm I need for the INPUT into the VSSB. All Ive gotten is that 95 is a bastard child and they did all sorts of crazy stuff.

    I can not use the stock one because it is in the tailshaft that is being removed to install my np205. So I need to get one of the inline mechanical to electric creators.
    I do plan to use the VSSB because I read I need it to send a signal for the transmission.

    So does anyone know that for a true 95, is it a 2,4,8k ppm to be sent to the vssb.

  2. #2
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    I believe it is a 4kppm system. In order for the trans to shift correctly you will also need the DRAC module fo the 4wd as they are calibrated differently to allow for the low range in the tcase. http://www.gearhead-efi.com/gearhead-efi/doc/DRAC2.pdf goto this link it will give u i fo on the drac and how to modify it to work for ur application.
    If it don't fit force it, if it don't force fit f&%@ it!

  3. #3
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    I dont know what a DRAC is. But my transfercase is all old school mechanical, no electronics. The truck i'm pulling everything from is 2wd, and I'm modifying the trans to accept my np205

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    Fuel Injected! 1BadAction's Avatar
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    Use a cable to VSS converter. It will screw into the fitting on the tail shaft of the T-case and the speedo cable will screw into it. That will send a VSS signal to the ECM, while still allowing your cable driven speedo to function.

    You will also need a way to tell the ECM that the truck is in low range, usually it's a switch to ground on the shifter. This may be where the DRAC comes into it, but I only know the later ECMs that just used a direct input.
    Last edited by 1BadAction; 10-28-2013 at 09:06 PM.
    94 Blazer, Turbo'd 350 TBI - DD
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  5. #5
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    1bad, thats what I was talking about I need to buy. But they come in different pulse settings. I would like to get the right one the first time.

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    Should be 4k ppm. The DRAC is the "signal conditioner" from the vss to the ecm/pcm/ instrument cluster. Note: your speedo could be off as much as 20mph depending on your setup.
    If it don't fit force it, if it don't force fit f&%@ it!

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    So what your calling DRAC, I'm calling VSSB?

    Oh, i'm sure its gonna be off. Different tire size, different axle ratios. But just getting a signal is my first step.

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    Fuel Injected! 1BadAction's Avatar
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    Quote Originally Posted by dale View Post
    So what your calling DRAC, I'm calling VSSB?

    Oh, i'm sure its gonna be off. Different tire size, different axle ratios. But just getting a signal is my first step.
    Yes, blame GM for that one, lol. They called them DRACs or VSSBs in different years and models. Most people with TBI vehicles seem to call them a DRAC.
    94 Blazer, Turbo'd 350 TBI - DD
    1991 2500 Suburban Adventure truck - 4wd conversion, 4-link F/R, 582ci CNP Big Block with Terminator X EFI backed by a 6L90 and twin stick'd NP205 t-case
    2012 Porsche Panamera Turbo - Date night car :)
    1979 16' Action Marine/"Johnny Cash" Merc Bridgeport Champ Motor - Metalflake Maniac

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    Yes the vssb is also known as a drac module. Thats what i learned at as. And vehicle speed is kinda important to proper fueling and spart timing. Trust me on this. Had a pickup that would stumble and or die when coming to a stop, fixed the vss signal and all is well.
    If it don't fit force it, if it don't force fit f&%@ it!

  11. #11
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    My diagrams call is a VSSB, so that's what I'm calling it

    I know the speed reading effects a lot. I've played with some OBD2 tuning. But I just want it to get a reasonable reading. But Ive also thought this evening. Since I will need to get a mechanical speed reducer to make the reading in my dash correct. If I screw that inverter in after that, wont it be close for the ecm?

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    Fuel Injected! gregs78cam's Avatar
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    Correct me if I am wrong, but I thought the 4L60E, and 4L80E both put out a 40pp(revolution) signal to the DRAC/VSSB, which converts that to all of the required signals for PCM, Cruise, RWAL, etc. Notice that Pins C7, C12 are inputs and C13 is a 1:1 signal (40ppR) on a single line. What PCM are you using? Can you set the Flag "Vehicle Speed Not From DRAC"? If so then you don't need the DRAC/VSSB and can send the 4Kppm directly from the sensor to the PCM.

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    Last edited by gregs78cam; 10-31-2013 at 02:39 AM.
    1978 Camaro Type LT, 383, Dual TBI, '7427, 4L80E
    1981 Camaro Z-28 Clone, T-Tops, 350/TH350
    1981 Camaro Berlinetta, V-6, 3spd
    1974 Chevy/GMC Truck, '90 TBI 350, '7427, TH350, NP203, 6" lift, 35s

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    Greg, i believe your theory should work. But be prepared for smoke just in case ;)
    If it don't fit force it, if it don't force fit f&%@ it!

  14. #14
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    My understandings from reading the lovely web, was that it was 40ppm tell they went to the 4l60e, then it changed... and that's what I cant find.

    Also, that whatever pcm I am using(I forget at the moment) could take a 2000 strait from a vss (assuming axle, tire, gear ratio, etc etc did provide a true 2000).

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    The vss reluctor has 40 teeth(4L60E & 4L80E). I dont know of any obd1 pcms that take the vss signal directly from the sensor as they are PM generators which produce an AC voltage. 88-90ish sent vss to instrument cluster where the calcs were done and then sent to the ecm. Now i could be wrong and I am always open to construcive criticism so dont take what i say as gospel.

    With the being said, if the sensor/adapter at the t-case diven gear produces 4kppm as Greg mentioned, in theory the computer should be able to accept it.
    If it don't fit force it, if it don't force fit f&%@ it!

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