Speedo Gear Question - Ford Mustang Forum
 
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post #1 of 4 (permalink) Old 05-07-2013 Thread Starter
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Speedo Gear Question

I have a '95 GT Convertible. It was originally an automatic tranny car, but just before I bought it, it was converted to a T5. I have 265/35R18 on the rear. I believe the gear in the tranny is the stock one, but Im pretty sure the gear in the dash is for the Auto Trans. I am about 20% over on the speedo reading. When I am going 75mph on the GPS, my dash reads 90mph. I just need to know what gear I'm supposed to have in the dash, and what gear color Im looking for in the Tranny. ~Thanks!
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post #2 of 4 (permalink) Old 05-07-2013
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You don't change the gear in the dash (not even sure if there is one) when you do the swap, you change the speedo gear that goes in the transmission. You need to make sure you've got the one for the t-5 and not for the AODE still. I believe you need the yellow 18 tooth gear but I would double check that, unless you have a different gear in the rear end. I've got 3.73s so I had to replace the speedo drive gear as well as the speedo gear when I did my T5 swap.
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post #3 of 4 (permalink) Old 05-07-2013
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No gear in the dash...

First question - what is the rear end gear ratio?

Matt

2006 GT - Vortech polished w/ intercooler, Eibach suspension, Hurst short-throw, some other goodies - tuned by Paul's High Performance. It moves...

and it collects dust admirably while parked for repairs in the garage...

SOLD - 1995 Black Mustang GT, AODE. Loved it, but I had to let it go...

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post #4 of 4 (permalink) Old 05-09-2013
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Quote:
Originally Posted by alleymad95GT View Post
what is the rear end gear ratio?
+1, that's the first question.

The tire size you're running is very close to stock. If the gearing was correct, even with that tire size the speedometer should be within 2% of accurate. See here:

Tire Calculator

You need to know:
  1. Rear end gear ratio
  2. Effective [rear] tire diameter
  3. Transmission speedometer drive gear tooth count (8, 7, or 6)
Once you know those, use these calculators to find your correct driven gear:

Tire Height Calculator

Speedometer Gear Calculator

The stock speedometer drive gear for 90-95 T5s is an 8-tooth.

'94 Laser red 'vert. Still a 5-oh... for now
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