just bought a '98 GT 4.6, 5spd. the speedometer works but reads way faster then what it should, at 20mph it reads 90mph so on and so forth, the rpm's seem to work fine, but the Odometer and trip meter isn't advancing at all.

this is my first mustang, i am mechanically inclined but would like to get some words from the mustang guys them selves.

thanks in advance.

-Terrance

 

Stock rear gear was a 3.27,.. odds are the rear gear has been changed to a 3.73 or 4.10 and the speedo gear has not been corrected. And for point of interest. The T45 for 96 - 98 GT's has an 8 tooth internal gear. The largest external gear you can use is the 23 tooth Chrysler gear. Sadly,.. with the 7 tooth internal gear a 4.10 rear gear can not be corrected in the GT's. The 96 - 98 Cobra T45's have a 7 tooth internal gear. The 23 tooth gear works excellent with the 4.10 gear. And actually reports the 3.73 as a little slow. If you have a 3.73 it can be corrected with the 23 tooth gear. If you have a 4.10 you will need something like a Dallas Speedcal to correct it. That or swap the internal 8 tooth gear in the tranny and swap it for the 7 tooth from the Cobra.

As for the odometer and trip meter. This is typical of all 94 - 98 Mustangs. When your looking to buy one and the mileage is too good to be true,.. it usually is. The odometer in my 96 GT quit at 63k,.. but I can assure you that 6 years later the original mileage was not 63k. It was closer to 230k. Ask the previous owner how long ago the odometer quit working. If it was already broken when they got it,.. well,.. there is no telling how many miles are on that car. Ford dealers sell a repair kit. Very easy fix.

Hurst

 

I don't believe the rear gears were messed with, but I'll definitely look into it. From what I was told the clutch was just replaced and a sensor or plug of some sort was not put back? Could this be a possibility?

 

Negative.

Only 2 things can change the speedo accuracy on 96 - 98 Mustangs.
1: The rear gear was swapped to something different.
or
2: Either the speedo gear in the sending unit was changed (Highly unlikely) or the transmission was swapped to a Cobra version of the T45 which has the 7T internal gear (Also highly unlikely because the Cobra T45 uses a different cross member mounting location). The GT specific T45 has the cross member mount closer to the case. The Cobra version is on the end of the tail shaft. It either works or it doesnt work. There is no in between where it can give improper speedo readings.

The only way to alter the speedo calibration electronically on the 96 - 98 cars is with an aftermarket module like the Dallas Speedcal. It steps in between the gauge cluster and the vehicle speed sensor. You tell it what tooth gear is inside the transmission, what tooth gear is on the sending unit, then tell it what gear ratio is in the rear end and tell it what tire size is on the rear of the car and it then properly calibrates the speedo.

The clutch has nothing to do with how the speedo works. There is a speed sensor on the left (driver side) side of the transmission. It has a mechanical gear inside of it and then sends an electronic signal to a PCB in the gauge cluster. The manual transmission wiring harness performs only 3 functions. Plugs into the front and rear O2's, plugs into the reverse signal indicator and plugs into the vehicle speed sensor (The sending unit).

Hurst

 

I really appreciate it bud, thank you.

 

What is the "fix" for the odometer?

 

Dealers sell a repair kit. IIRC its just a small plastic gear that breaks when you push the trip reset button but effects the whole works.

Hurst

 

Ahh Thanks, mine just stopped, everything else works