Speedometer vs. scanner question
03-05-2010, 12:10 AM
#1
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Car: 1991 Z28 vert, 1988 GTA
Engine: 305 TPI, 305 Carb-finally runs!
Transmission: TH-700R4/BW WC T-5
Axle/Gears: 3.73 posi 4th gen 10-bolt/BW 9 bolt
Speedometer vs. scanner question
I have a 1991 Camaro Z28 convertible with TPI, auto, 3.73's. I replaced the speedo gears in the trans with ones for 3.73s, and also swapped in a 145 MPH speedo out of a 1990 IROC. I also have a Snap-On MT2500 red brick scanner.
Now that the basics are down, here is my issue. The scanner is reporting a speed different than that of the speedo. The speedo reads 10-20 MPH higher than the scanner, and the faster I go, the more off it gets. Since our gauges are not known to be the best ever, I'm trusting my scanner for an accurate reading. The speed the scanner shows appears to me to be pretty accurate with traffic on the road with me. What I'm wondering, is how to fix this.
I had the cluster apart to fix the tach (which it is now
) and noticed there is another little circuitboard under the speedo. Is this some kind of drive board for the speedo? Since the speedo is the only thing I swapped into the cluster (all the other gauges stayed), could I need the board from the 145 MPH cluster (which I think I still have) to make it read correct?
Also, one more thing; I notice that the speedo needle never rests on the little peg when off; I can't remember if I ever pulled the needle off or not, but if I did, could that be causing my symptom because the needle simply isn't "zeroed"?
Thanks anyone for any help you have!
Now that the basics are down, here is my issue. The scanner is reporting a speed different than that of the speedo. The speedo reads 10-20 MPH higher than the scanner, and the faster I go, the more off it gets. Since our gauges are not known to be the best ever, I'm trusting my scanner for an accurate reading. The speed the scanner shows appears to me to be pretty accurate with traffic on the road with me. What I'm wondering, is how to fix this.
I had the cluster apart to fix the tach (which it is now
) and noticed there is another little circuitboard under the speedo. Is this some kind of drive board for the speedo? Since the speedo is the only thing I swapped into the cluster (all the other gauges stayed), could I need the board from the 145 MPH cluster (which I think I still have) to make it read correct? Also, one more thing; I notice that the speedo needle never rests on the little peg when off; I can't remember if I ever pulled the needle off or not, but if I did, could that be causing my symptom because the needle simply isn't "zeroed"?
Thanks anyone for any help you have!
03-05-2010, 09:44 AM
#3
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Car: LOWERED ♦ CRIMSON METALFLAKE
Engine: ► 400 KUBES ◄
Transmission: 765R4
Axle/Gears: EATON POSI 4.56
Needle In A Haystack (Of Speedometers)
First make sure you get the needle replaced to zero MPH.
But that isn’t the only problem based on your complaint.
When connecting the scanner to the ALDL it’s reading from the VSS.
Therefore if the wrong VSS drive gear is used the scanner is essentially useless.
You can use a GPS receiver to monitor your speed.
You need the 145 driver board.
◙◙◙◙◙◙◙◙◙◙◙◙◙◙◙
Happy Racing!
But that isn’t the only problem based on your complaint.
I'm trusting my scanner for an accurate reading.
Therefore if the wrong VSS drive gear is used the scanner is essentially useless.
You can use a GPS receiver to monitor your speed.
the faster I go, the more off it gets
◙◙◙◙◙◙◙◙◙◙◙◙◙◙◙
Happy Racing!
◙◙◙◙◙◙◙◙◙◙◙◙◙◙◙
If People Drove Any Slower They’d Be Going Backwards
When you see fog or “running” lights on in good weather beware. WLow performance driver ahead.
How bout those nitwits too scared to drive without headlights in the daytime
and the nitwits that need headlights for a little rain
.
.
If People Drove Any Slower They’d Be Going BackwardsWhen you see fog or “running” lights on in good weather beware. WLow performance driver ahead.
How bout those nitwits too scared to drive without headlights in the daytime
and the nitwits that need headlights for a little rain.
.
Last edited by NINÅ; 03-05-2010 at 12:32 PM.
03-05-2010, 11:22 AM
#4
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Car: 1991 Z28 vert, 1988 GTA
Engine: 305 TPI, 305 Carb-finally runs!
Transmission: TH-700R4/BW WC T-5
Axle/Gears: 3.73 posi 4th gen 10-bolt/BW 9 bolt
Re: Needle In A Haystack (Of Speedometers)
good idea with the GPS James, I never even thought of that. I'll get my hands on one and use it to verify the gauge and scanner...if the scanner is right (or within a mile or 2 at 65), then i will zero the speedo needle next, and if that doesnt get me quite close enough, then i will try and find the cluster the 145 speedo came out of and swap boards based on Nina's reccommendation (than you as well, Nina!)
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