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Thread: Speedo sensor

  1. #11
    Join Date
    Jun 2003
    Location
    Brackley, Northants, England.
    Posts
    826
    If the manufacturers of the sender unit thought it was a good idea to ground one side why didn't they already ground one side at the sender? Similarly why have some owners had problems and gone to the trouble of putting a sender on the prop shaft because they couldn't make the Gearbox unit work?

    Large electrically noisy currents circulating in the chassis cause small voltage drops in series with the tiny speed sender signal. Clearly whether it works or not depends on a large number of factors such as is the Battery at the front or rear of the car and also where the various earthing points are. I can accept grounding one side will work in many cases but you won't convince me that it's the right thing to do.

    As an example, to avoid these circulating chassis currents, CAN bus wiring in Tin Tops even though they carry much larger signals, never rely on a ground and a single wire for communicating they always use two wires neither of which is connected to chassis ground. The correct way of connecting the Tremec unit is to route both pins direct to the speedo where one of the wires is grounded. This way no circulating chassis currents can directly corrupt the sender signal. Frankly this is pre-school playgroup automotive electrics.

    Nobody has to listen to my advice but when you find grounding one side of the sender doesn't work properly you might like to try doing it correctly and use two wires.

    Denis

    If you take something to bits often enough, eventually you'll have two of them......


    GD427E039

  2. #12
    Join Date
    May 2004
    Location
    Cowbridge, United Kingdom
    Age
    61
    Posts
    9,930
    Two of my three builds have used the Tremec sender without issue.
    I used a screened cable on one but not the other.
    The first car had a mechanical speedo.
    Kev Davies
    South Wales Area Rep. UKCC Membership Secretary
    DAX Mk4, 383 Chevy Stroker, Tremec. SOLD
    Contemporary CCX 3-4028, 445ci Big Block FORD FE,TKO 600, Old School IVA'd and SOLD
    Dax De Dion LS2 and T56 IVA'd June '17 SOLD
    1965 Ford Mustang 289 Convertible FOR SALE
    In build- Hawk 289 Sebring

  3. #13
    Join Date
    Oct 2015
    Location
    helmshore
    Age
    50
    Posts
    61
    Just to add to this I have a tremec t5 box with a 3 wire sensor, 1 is earth 1 is pulse to speedo and 1 is live feed, problem is I don't know which is which,can any body help?

  4. #14
    Join Date
    May 2012
    Location
    near Thame
    Age
    41
    Posts
    151
    Quote Originally Posted by oglyoodoo View Post
    Long time since I've been here...

    I can't see the point in faffing around with a Prop Shaft sensor for the speedo when you already have a perfectly adequate Sender unit inside your TKO600 which needs no adjustment.

    Do an advanced search here looking for "Screened cable" and written by "Oglyoodoo" and you'll find the info you need in a post I wrote in 2013.

    There's a lot of useful info on this forum if you look.

    Denis
    Thank you for this heads up Denis, it's perfectly timed for me as I've just fitted my engine and tko600 box.

    I'll follow your recommendations and see how it goes.

    Thanks Greg
    Building MK4 GD Jag based with a Chevy 383/tremec tko600.

    Build blog/photo store https:/www.facebook.com/pg/gregsGD427

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