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Author Topic: VSS confusion  (Read 14741 times)

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GTRS Fiero

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VSS confusion
« on: August 17, 2019, 05:27:59 pm »
My speedo has been 10 MPH off since the change to the 4T60.  It was correct on the THM125C.

We tried a different VSS.  No change.

The ECU and speedo both show the same speed.  Since I was getting my gauges calibrated, included the speedo.  No change.

The VSS gear is blue.  Today, I replaced the blue gear with a white (or beige) gear, which does have an additional tooth.

Are you with me, so far?

Get this.  No change.

Color me confused.
« Last Edit: August 31, 2019, 08:26:35 am by GTRS Fiero »
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scottb

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Re: VSS confusion
« Reply #1 on: August 17, 2019, 05:54:44 pm »
What is the percentage of change in the gear ratio between the transmissions?
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GTRS Fiero

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Re: VSS confusion
« Reply #2 on: August 17, 2019, 05:57:29 pm »
Um, both supposed to 3.33, but I may have misunderstood your question.
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scottb

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Re: VSS confusion
« Reply #3 on: August 17, 2019, 07:39:01 pm »
Thats what I was curious about...... the only thing that I can think of is the transmissions and speedometers were calibrated for different size tires. In my mind you will have to adjust  the gears by the same percentage as the tire size difference. ....... in others words if the tire difference is 15% you have to adjust the tooth count by 15%. It makes sense in my mind
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GTRS Fiero

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Re: VSS confusion
« Reply #4 on: August 17, 2019, 08:24:30 pm »
The thing is, I increased the tooth count.  No change to the speedo.
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Fierofool

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Re: VSS confusion
« Reply #5 on: August 17, 2019, 08:34:42 pm »
On the manual trans, one tooth only changes it 2 or 3 mph at 60. 
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GTRS Fiero

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Re: VSS confusion
« Reply #6 on: August 17, 2019, 08:37:19 pm »
There are only 2 speedo gears for the auto.  I'm using the one with the most teeth.
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GTRS Fiero

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Re: VSS confusion
« Reply #7 on: August 18, 2019, 01:18:26 pm »
It looks like a 12% error.
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Fierofool

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Re: VSS confusion
« Reply #8 on: August 18, 2019, 01:43:01 pm »
That's not an electronic transmission?  You're running a 7730 ECM?  Wonder if the table can be reprogrammed for your tire size.  You would need to know the original tire size of the car the trans came from, then find that tire size calculator on PFF to match the diameter, or reprogram to make the adjustment. 
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There are three kinds of men:

1.    The ones that learn by reading.
2.    The few who learn by observation.
3.    The rest of them have to pee on the electric fence and find out for themselves.    Will Rogers

GTRS Fiero

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Re: VSS confusion
« Reply #9 on: August 18, 2019, 01:45:47 pm »
I have Ryan working on that angle.
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GTRS Fiero

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Re: VSS confusion
« Reply #10 on: September 22, 2019, 09:58:55 am »
Quote from: Fierofool on August 18, 2019, 01:43:01 pm
That's not an electronic transmission?  You're running a 7730 ECM?  Wonder if the table can be reprogrammed for your tire size.  You would need to know the original tire size of the car the trans came from, then find that tire size calculator on PFF to match the diameter, or reprogram to make the adjustment.

Ryan says no.    :(
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GTRS Fiero

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Re: VSS confusion
« Reply #11 on: September 22, 2019, 10:00:20 am »
I want to do everything possible to avoid using the problematic Dakota Digital box.

I think that the problem may be in the VSS unit itself.  I'm going to try using the original VSS with the new gear.
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GTRS Fiero

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Re: VSS confusion
« Reply #12 on: September 25, 2019, 07:13:46 pm »
I'm wondering if I have the wrong VSS.
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Fierofool

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Re: VSS confusion
« Reply #13 on: September 25, 2019, 09:22:21 pm »
Is the one from your transmission interchangeable with that from another series transmission? 
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There are three kinds of men:

1.    The ones that learn by reading.
2.    The few who learn by observation.
3.    The rest of them have to pee on the electric fence and find out for themselves.    Will Rogers

GTRS Fiero

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Re: VSS confusion
« Reply #14 on: September 25, 2019, 09:24:10 pm »
Dunno.  The Fiero VSS is rather unique.  I can't pin that down.
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