For those with Ford 9 inch rears, what did you do to make the speedo accurate?

[V6UnderPressure]

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Obviously, most TRs have 3.42 gears. With the Fords, the closest is 3.50. If you wnet this route, how off was it? I guess a taller tire would even things out, but would like to hear experiences here.

 

[dsapper]

Depends on what trans you have and what gauges. Assuming stock gauges, stock trans and stock tire height, you can change the speedo gear at the transmission.

 

[coach]

.08 of one revolution? I don't think it would be off at all. Going from factory tires to 275's must be within 5 mph as most run Eric's chips and there is no threads about it messing up the chip settings. The tire difference is way bigger then the gear difference. I do not think I would worry about it.

 

[charlief1]

The speedometer isn't exact from the factory and a .07 change in gearing might make it off or possibly dead nuts. None of the old mechanical speedos are 100% accurate without having everything exactly as the factory made it. Even then they'll still be off slightly because there's no real way to make it 100% accurate because of mechanical variance on a product.

 

[V6UnderPressure]

Figured that. Im a numbers guy, just wanted some reassurance.

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[TexasT]

http://www.transmissioncenter.net/speedometer_calibration_______va.htm

If you scroll down the page there is a 2004r section with a chart with tire heights, rear gears(though it is gm ratios) and a list of what gears one might use.

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