I just picked up an 89 mustang gt. I was told that it is completely stock except that it has been painted and the exhaust has been replaced. I noticed it before i bought the car that the speedometer is a little off. Ill be doing 25-30 and it will read 40-45 mph. Ive searched the forum and havent really found anything. It should be stock so i should have stock wheels and a stock rear end and hopefully stock gauges. It is a 140 speedometer. what is going on here and does anyone know how to fix it? Thanks a lot guys.
speedometer calibration
- Thread starter Marks89GT
- Start date
No.11
10 Year Member
you should the gear ratio yourself to make sure. jack up the rear and put the car in neutral. then turn the wheel one full turn while taking note of how many times the driveshaft turns. that'll give you an idea of the ratio.
or perhaps someone replaced the speedo gear with one that doesnt match.
or perhaps someone replaced the speedo gear with one that doesnt match.
trbkrb
Founding Member
Sounds like it has gears, and does not have the correct speedometer gear. Do as No 11 said, 3-1/2 driveshaft turns would be 3.55 gears, 3-3/4 turns 3.73. Then you can pull the speedometer cable and see what gear it has, note the color and number of teeth.
No.11
10 Year Member
ok sounds like you have the red 21 tooth gear. what you need is the beige colored 19 tooth gear.
here is a chart showing what you need.
Mustang Speedometer Gear Application Guide - LRS
here is a chart showing what you need.
Mustang Speedometer Gear Application Guide - LRS
this looks what i need but i think its what i already have...
1983-95 Mustang 19 Tooth Speedometer Gear & Clip Kit, Manual Trans at LRS - Same Day Shipping!
1983-95 Mustang 19 Tooth Speedometer Gear & Clip Kit, Manual Trans at LRS - Same Day Shipping!
trbkrb
Founding Member
Lot of info here, but if you do have 2.73 gears in a 89 manual car, stock it has a maroon 16 tooth gear on the cable. The drive gear inside the trans is a yellow 7 tooth gear. That is what my car had stock. All three have to match to get the correct reading. In order for the speedo to read fast, the rear gears would have to be numerically higher, turning the cable faster, or the speedo gears have to have fewer teeth, thus turning the cable faster. If you have the red gear, the cable would be turning slower, not faster. I would double check the speedo gear and count the teeth and if you can look inside the trans, check for the yellow gear. If everything is right, then I would suspect the speedometer is bad.
trbkrb
Founding Member
Another thing I just thought about, could they have replaced the gauge faces? The 140 speedo came out mid year in 89, maybe they put a 140 face on a 85 speedometer? That would make it read fast for sure.
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