Automatic gear's help

dusty430 · Apr 6, 2005

Hello,

When I bought my 01 mustang Gt w/automatic. I seen that the diffrential cover was replaced. With this in mind, I was wondering if the gears have been swaped in my car. I have 20" rims in the back and 18" rims in the front. Tire size is 245/40ZR20 in the back and 245/40ZR18 in the front. I was driving at 75 mph at 1700 RPM however my speedo is off by 5 mph due to the tire size. I was really going 70mph at 1700 RPM. Any help would be highly appreciated because I want to put 4:10 in but I don't know what I have.

Thanks,
Dustin

CanadaStang · Apr 6, 2005

this should help:
http://www.allfordmustangs.com/Detailed/636.shtml

dusty430 · Apr 7, 2005

I am still confused this is my results
Your Rear Gear Ratio is : 2.0035 (Toploader or C4)
Your Rear Gear Ratio for OverDrive is : 3.0053 (T5 or AOD)

I thought that stock was 3.13?
Why am I so low?

streetstang03 · Apr 7, 2005

why such big wheels? only 245s on those things

jeffnoel · Apr 7, 2005

dusty430 said:
Hello,

I was driving at 75 mph at 1700 RPM however my speedo is off by 5 mph due to the tire size. I was really going 70mph at 1700 RPM.

Thanks,
Dustin

You've got it backwards a taller tire means your speedo is reading low not high, so when your speedo says 75 your actually doing 81 if your speedo was recalibrated for the 20s. But with a tire 2" taller than stock I wouldn't believe what your speedo says at all. The easiest way for you to check what gears you have is to raise the rear off the ground and rotate a tire 1 full turn and count how many time the driveshaft turns. What does the diff cover look like are you sure it's not stock?

dusty430 · Apr 7, 2005

I used one of those on the side police scanners to tell the speed. It is always 5mph faster. The cover isn't black. Ill try what you said

Cobra Jay · Apr 7, 2005

jeffnoel said:
The easiest way for you to check what gears you have is to raise the rear off the ground and rotate a tire 1 full turn and count how many time the driveshaft turns. What does the diff cover look like are you sure it's not stock?

dusty430 said:
The cover isn't black.

The covers aren't black from the factory, they come in a natural or zinc plated finish.

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