North American Turbocoupe Organization



Speedometer different calibration in automatic versus standard?
anasazi4st Offline
Senior Member
#11
(07-23-2021, 01:25 AM)vegas_ss Wrote: Yes, that was what I was thinking of trying.  Would like to get it pretty accurate for 25 - 55 mph.  Will try and gauge ~ 3-4 mph difference.

A couple of years ago I purchased a 140mph conversion kit from eBay. It was an easy enough project, but the speed readings—like yours—vary across the gauge.

My OEM speedometer was off by around 3 mph, which I got used to over the years, but this one is off by as much as 7 mph at 85–it diverges farther apart from there, so at 90 it’s almost 10 mph, and so on.

I complained to the company—in the eBay listing they claimed that they test every kit with a working model speedometer. After several emails it became obvious that they did not in fact test our TC speedos—they said that they could not duplicate the problem so they could not offer a solution. This back-and-forth took months. After a while it also became obvious that they were either too busy, too lazy or too apathetic to pursue a fix, and I received a refund. When I asked if they were going to pull this particular kit off the shelf, the response was that they would still try and figure out what was wrong and would let me know how I might fix it.

I have a GPS in the Navigation mode of my media entertainment center I put in a few years ago, and whenever I can I use that. I know at least one former member (in addition to Jeff) created his own homemade version, if you know electronics its not that hard.
Another proud dues-paying member.

1987 Turbo Coupe w/T5OD, 8.8 axle, grey smoke; most options. Got it in 1991 with 41K miles: 3 turbos, 2 heater cores, 1 T5OD full rebuild, 5 clutches, 1 head gasket, 2 Teves II ABS units, etc. later....
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vegas_ss Offline
Senior Member
#12
I did reposition the needle to just about a needle width below zero (was quite a bit below) and went for a quick drive by the radar speed warning which is set to flash your speed above 35. Had the speedometer showing a pretty steady 40 mph and the sign flashed 40 so it looks good. I'll test it out with the GPS to verify a wider range of speeds in the next couple of days and see. Dealing with the IVR now so hopefully I can get the dash back together soon.
1987 TC, 5sp, Boport Stage 3 Head/2.1 Cam
1996 Impala SS
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vegas_ss Offline
Senior Member
#13
Speedometer now is spot on according to the GPS at speeds up to ~ 65 mph, then reads a little fast ~ 2 mph once at 70+ so that's fine for me! Thanks Jeff for the moving the needle info! Seems at rest mine is ~ a needle width below zero right now, curious as to how others are?
1987 TC, 5sp, Boport Stage 3 Head/2.1 Cam
1996 Impala SS
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