Speedometer calibration

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May 19, 2009 | 05:53 PM

Hello, Michael

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Joined: May 2008

Posts: 286

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From: Cicero, IL.

Car: 1987 Pontiac Firebird Trans Am WS6

Engine: SBC 350

Transmission: T-56

Axle/Gears: 3.70:1 BW M78 9-Bolt Posi

Speedometer calibration

I swapped gears and need to correct my speedometer. I have an 87 Trans Am with the 700R4 and it has a VSS. What can I do to correct my speedo? I know some companies sell a "black box" that you can connect inline from the VSS to the PROM. I'm assuming this is my only option. The car has a digital dash. Does anyone know who sells them for a reasonable price. I've seen one from speedometer world, but its $169.

May 19, 2009 | 07:01 PM

1989GTATransAm

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Posts: 6,859

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From: Cypress, California

Car: 1989 GTA

Engine: 369 TPI

Transmission: 4L60E

Axle/Gears: 3.70 Nine Bolt

Re: Speedometer calibration

I know of two options. One is to change the gears that drive the VSS on your 700R4. 2nd as you suggested is to buy the Dakota Digital Box that will allow you to adjust the VSS signal. Either will work just fine.