23 tooth speedo gear?

A

anthony hill

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Nov 12, 2008

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Jan 25, 2010

#1

• Jan 25, 2010

• #1

I just got a new speedo cable and a 23 tooth gear because I have 4:10s, I know that my speedo still wont be right on but does anyone know how far it will be off? Its a 91 gt with a 5spd. Thanks guys!!!

 

tannerc91gt

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#2

• Jan 25, 2010

• #2

I think it's like 12-15mph, but you can switch the drive gear to a 6 tooth and it will be MUCH closer, that's what I'm in the process of doing

 

Mr. Rustypwnz

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Jun 1, 2005

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Jan 25, 2010

#3

• Jan 25, 2010

• #3

yeah it will be around what tanner said.. call up tony at astro performance, and he will set ya straight. He's good people..

 

SVT32VDOHC

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Jan 25, 2010

#4

• Jan 25, 2010

• #4

The faster you are going, the further it's off (reading faster) At around 90, it told me I was going like 75-77MPH. I had my Dad follow me in his Chevy truck that time, so I know it's 100% accurate. At around 50MPH, I think it would read like 43-45MPH.

 

A

anthony hill

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Nov 12, 2008

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#5

• Jan 25, 2010

• #5

tannerc91gt said:

I think it's like 12-15mph, but you can switch the drive gear to a 6 tooth and it will be MUCH closer, that's what I'm in the process of doing

Click to expand...

But dont you have to get inside the tranny to do this?

 

foxmustangman

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Jun 20, 2007

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Jan 25, 2010

#6

• Jan 25, 2010

• #6

You have to take off the back housing, but if its a later transmission the housing doesn't come off

 

Dino Dino Bambino

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Jan 26, 2010

#7

• Jan 26, 2010

• #7

anthony hill said:

I just got a new speedo cable and a 23 tooth gear because I have 4:10s, I know that my speedo still wont be right on but does anyone know how far it will be off? Its a 91 gt with a 5spd. Thanks guys!!!

Click to expand...

In stock form your '91 GT would have had a 3.08 rear end, the tranny will have an 8-tooth drivegear on the output shaft, and the speedo gear would have had 20 teeth.
With your mods, the speedo will be overreading by about 16%. If you replace your 8-tooth drivegear with a 7-tooth, the speedo error will be reduced to just 1%.

 

tannerc91gt

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#8

• Jan 26, 2010

• #8

My stock 91 had 2.73s....

 

fiveohwblow

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#9

• Jan 26, 2010

• #9

As did mine.

 

Dino Dino Bambino

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#10

• Jan 26, 2010

• #10

tannerc91gt said:

My stock 91 had 2.73s....

Click to expand...

Is yours manual or automatic?
If the original axle gears were 2.73, the speedo gear would have been 18-tooth instead of 20. With a 4.10 axle gear and a 23-tooth speedo gear, the speedo will overread by 18%. The remedy is still the same. Replace the 8-tooth drivegear with a 7-tooth and the speedo error is reduced to just 3%.

 

tannerc91gt

This last 25% is foreign territory at this point

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#11

• Jan 26, 2010

• #11

Manual. I also thought it was replacing the 7 tooth drive with a 6 tooth.

 

HotFox

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Jan 26, 2010

#12

• Jan 26, 2010

• #12

You could buy a ratio adapter, this is what I did for my 4.56 rear gears. They will make you any ratio if the ones they got will not work for you.

Speedometer Gear, Speedometer Gears, Ford, GM, Dodge 700R4

Scott