tadpole1969

ok got a ?, im changeing gears in my mustang to a 3.73 gear its a automatic trans with over drive , what i need to know is can i put a new speedo gear on this to correct speedometer reading? so transmission will shift correctly or?

tadpole1969

anyone know?

dawson1112

NO you have to have it programmed with a tune, or buy a speed cal.


These year cars don't have a speedo gear, they use a magnetic pickup that reads a reluctor ring inside the trans.

01S2Roush

My speedometer shows 10 mph too fast, I'm assuming the previous owner did a gear swap. I'm changing the gear oil tomorrow and am wondering how I can tell what gears are in by looking since I'll have the cover off. Also couldn't we just recalibrate the speedometer by pulling the cluster and readjusting the needle to a gps?

tadpole1969

ok thats what i needed to know thx! im going to by this tuner monday 7015 SCT X4 POWER FLASH PROGRAMMER TUNER FORD DIESEL & GAS , been wanting one anyhow for awhile

01S2Roush

Great hope the tuner does good for ya, but anyone know if adjusting the needle on the speedometer with a gps will work? This would give me an excuse to put in some white face gauges and calibrate at the same time lol.

dawson1112

Never heard of it done. Your not telling the computer how fast your traveling, mileage will be off and autotrans wont shift properly. As well as some other things it needs to know. The engine may idle to high or low when pressing the clutch in coming to a stop.

dawson1112

The gears should have the ratio stamped into the ring gear someplace that you can read with the cover off. If not you can lift the rear of the vehical, make a mark on the inside of the rear wheel, then rotate it 1 full turn counting the number of revolutions the drive shaft makes. So if the gears are 3.73 the drive shaft would rotate just a tiny bit under 3 3/4 turns.

3.27 gears the drive shaft would rotate just a tiny bit over 3 1/4 turns per 1 revolution of the tire.

tadpole1969

got another question dawson ,i think i currently have a 3.27 gear but not sure! at 70 mph rpms are at like either 2000 rpms or 2100 rpms just cruizing so would that be rigth for 3.27 gears or?

dawson1112

Probly about right, I think that's where mine sits at 70mph with stock 3.27 gears.

You can do the above procedure to know for sure. Wheels off the ground , count the drive shaft rotations per 1 revolution of the tire.