[DeTomaso] Speedometer Calibration Problem GT5-S Amerisport 1987

MikeLDrew at aol.com MikeLDrew at aol.com
Sat Jul 14 11:59:19 EDT 2012


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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