JLS-SN95
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If I change the gear ratio in my 96 4.6 GT how do I correct my speedometer and odometer accuracy?
Gear Ratio Change & Speedometer Correction
- Thread starter JLS-SN95
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Wmac
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JLS-SN95
New Member
I'm new to all this, so I'm trying to understand this chart and what I need. I have the T45 5s speed transmission, current gear ratio is 3.27, I want to go to 3.73. Is this telling me I only need to change the gear in the dash?
Wmac
Active Member
No, since you have a T-45 with an 8 tooth drive gear, only the driven gear needs to be changed. It's on the vss, which goes into the trans. If you have a "stock" size tire like a 245/45/17, then the formula would be: 8x3.73x812/1000=24.23
The only gear that is close, is a 23 tooth. Try LMR or CJ Pony.
The only gear that is close, is a 23 tooth. Try LMR or CJ Pony.
JLS-SN95
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MUCH THX!!!!
Great info!
SPeace-ATL
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CAUTION!!!
For a 96-98 GT T-45 the internal gear is the 8-tooth which is only good for calibration up to a 3.27 differential with nominal tires.
A 3.55 or 3.73 or 4.10 will require a Speed Calibration Device to be installed to get the speedometer accurate.
The references to any speedometer "driven" gear on the VSS with more teeth than 21 are all aftermarket gears that will work, but only for a few months before it chews off all the teeth.
These 23 tooth gears referenced above will also eventually ruin the internal speedometer gear rendering the speedometer drive useless until the gear is replaced inside the transmission.
The 23t gears mentioned are TRASH. I have a collection of them in my junk bin that I have removed from transmissions over the years. They should not even be offered... The gear teeth have to be paper thin to get 23 teeth around the gear. No GOOD!
The 96-98 COBRA T-45 has a 7-t internal gear that will calibrate up to the 3.73 differential without a Speed Calibration Device. If you can get your hands on a 7-t internal gear the transmission tail section still has to be opened in order to install it.
For Reference, the 1999-2001 T-45 transmissions have an electronic "OSS" speedometer pickup. Those are calibrated electronically in the programming of the "tune" of the ECM.
Stan
For a 96-98 GT T-45 the internal gear is the 8-tooth which is only good for calibration up to a 3.27 differential with nominal tires.
A 3.55 or 3.73 or 4.10 will require a Speed Calibration Device to be installed to get the speedometer accurate.
The references to any speedometer "driven" gear on the VSS with more teeth than 21 are all aftermarket gears that will work, but only for a few months before it chews off all the teeth.
These 23 tooth gears referenced above will also eventually ruin the internal speedometer gear rendering the speedometer drive useless until the gear is replaced inside the transmission.
The 23t gears mentioned are TRASH. I have a collection of them in my junk bin that I have removed from transmissions over the years. They should not even be offered... The gear teeth have to be paper thin to get 23 teeth around the gear. No GOOD!
The 96-98 COBRA T-45 has a 7-t internal gear that will calibrate up to the 3.73 differential without a Speed Calibration Device. If you can get your hands on a 7-t internal gear the transmission tail section still has to be opened in order to install it.
For Reference, the 1999-2001 T-45 transmissions have an electronic "OSS" speedometer pickup. Those are calibrated electronically in the programming of the "tune" of the ECM.
Stan
Wmac
Active Member
Stan:
We are fortunate to have someone with your manual trans knowledge share your opinion. I sure do appreciate when you take the time to comment.
If anyone was considering changing an 8 tooth drive gear, wouldn't a 6 tooth (black) gear be a better option? Then they could use a Ford driven gear up to 4.30 rear gear.
That's what I did when I swapped to a T5 last year with 4.10 gears. A 20 tooth driven gear is close to actual speed.
We are fortunate to have someone with your manual trans knowledge share your opinion. I sure do appreciate when you take the time to comment.
If anyone was considering changing an 8 tooth drive gear, wouldn't a 6 tooth (black) gear be a better option? Then they could use a Ford driven gear up to 4.30 rear gear.
That's what I did when I swapped to a T5 last year with 4.10 gears. A 20 tooth driven gear is close to actual speed.
What's the situation with T5 in a '94 GT? Up to which tooth count driven gear is it safe to use, without changing the internal gear?
Wmac
Active Member
See chart above.
Your T5 will have an 8 tooth drive gear. 21 tooth for 3.27 gears or 23 tooth for 3.55 gears. Or use a speed calibrator.
Your T5 will have an 8 tooth drive gear. 21 tooth for 3.27 gears or 23 tooth for 3.55 gears. Or use a speed calibrator.
A speed calibrator is like this one for example?
SPeace-ATL
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Yes, the ABBOT should be able to recalibrate the speedometer. Just know not to use a gear on the VSS with more than 21 teeth or the gears will tend to disintegrate.
