[DeTomaso] Speedometer Calibration Problem GT5-S Amerisport 1987

[Julian Kift]

I believe there are actually a number of permutations that could be at fault here.

1. There are the two brands of angle adapter (Borletti and VDO), but each brand is available in two ratios, 1:1 and 1.1:1 IIRC. Later cars are typically using a VDO angle drive.
2. Two speedometer revolutions are also available 1600 revs per mile and 1200 revs per mile (or something close to that for each)
3. To compound those computations further speedo face plates are often changed, so if (like my GT5) this car was originally a Euro car with km/hr speedo someone may have innocently just changed faceplate to mph (this is was what happened to my GT5) assuming all would be good and it's not.

Establishing what you have for speedo and angle drive is a good starting point as I imagine you have a mismatch somewhere being so far out on indicated vs. actual speed. Modern vs. original spec tire diameters are typically going to give within a 10% error.

Good luck,
Julian

> From: MikeLDrew at aol.com
> Date: Sat, 14 Jul 2012 11:59:19 -0400
> To: montana at montanas.com; detomaso at realbig.com
> Subject: Re: [DeTomaso] Speedometer Calibration Problem GT5-S Amerisport 1987
> 
> 
> In a message dated 7/14/12 8:12:50 AM, montana at montanas.com writes:
> 
> 
> > I am restoring a 1987 GT5-S and have had the speedometer calibrated 3 
> > times
> > and it still remains approximately 135 % under reading versus actual 
> > speed.
> > ( Gauge-55, GPS-75, Error 20, Ration-136.4%)  This error factor remains
> > constant through the 30-70 gauge test.
> > The mileage and the odometer test results in 8.0 miles reading versus 
> > actual
> > 10 miles traveled.  The 52 ft., 9 & 1/2 in. cable rotation test is 12.63
> > turns within the test distance.
> > Advice would be most appreciated.  Ken Montana, Biloxi, MS, USA,
> > 228-832-1313, montana at montanas.com
> > 
> 
> Ken--the Pantera originally came with tires that were 27-ish inches tall 
> and the speedos were calibrated thusly.   Cars like yours fitted with original 
> wheels and 24-inch tires will therefore normally register much higher at a 
> given actual speed because the rear wheels are turning faster to travel at 
> the same groundspeed.
> 
> It sounds like somebody has attempted to correct for this by fitting a 
> different angle drive to the speedometer, OR installing some sort of correction 
> box in the middle of the system somewhere (likely behind the dash).   But 
> clearly it's not working--or rather, it's working TOO well.
> 
> Notice the two different styles of speedo adapter, seen here:
> 
> http://www.panterasbywilkinson.com/webpages/catalog/ill10c.html
> 
> There are also two different VDO adapters with different characteristics.   
> I have to admit that I can't remember ever actually seeing a VDO-style 
> adapter; every car I've paid attention to has had the Borletti style.
> 
> What do you have?
> 
> As an aside, I wish I had known you were there in Biloxi--Lori and I were 
> just there for a week, two weeks ago, visiting her son who is a special ops 
> boat guy (like in the movie "Act of Valor") and stationed at the Stennis 
> Space Center.   We'll have to try to get together next time we come out there 
> for a visit....
> 
> Mike
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