what is going on here???

[87foxstang]

ok, as you can see in my sig i have 4.10 gears, well that was like the only mod to the car when i bought it 3 years ago, at least thats what the guy said. Sometimes i doubt they are 4.10's. So i tried the test the other day, jack the car up put it in first gear, rotate the tire and watch how many rotations the driveshaft makes for every one turn of the tire. Well everytime i try this i only get 1 3/4 rotation of the drivesaft for one turn of the tire!!!WTF I may have posted this in the past but i always think im doing it wrong so i try it again, and always the same thing!!! help would be appreciated lol thanks guys i just want to know what gears i REALLY have
sorry for the long post

 

[5spd GT]

Your test isn't working out right

What rpm are you cruising at at 70mph?

 

[87foxstang]

not sure about 70mph, i dont go that fast

but at 65 its at about 2800 or so

 

[grey5.0beast]

You are supposed to put the car in neutral. get under there with a marker or something and just watch very carefully.

 

[grey5.0beast]

not sure about 70mph, i dont go that fast

but at 65 its at about 2800 or so

Sounds like 4.10s to me. I cruise at 60 in 5th and its at 2k rpm with 3.73s

 

[5spd GT]

2,800 at 65mph?

Sounds like either a short tire and 4.10's...or your looking at 4.30/4.56 gears.

 

[87foxstang]

ohh neutral huh, i thought i tried it both ways and it still didnt add up lol i guess ill have to give it yet another shot this weekend so 3.73's at 60 is 2k huh, so maybe i do have 4.10's

 

[87foxstang]

as far as a small tire, i think its bigger than stock, i have a 245/50/16

 

[5spd GT]

as far as a small tire, i think its bigger than stock, i have a 245/50/16

Those are shorter tires, but barely.

The 245/50/16's (which is what I have) is 25.64" tall.

The stock 225/55/16's are 25.74" tall.

That difference will not be seen on a stock mechanical tach.

Shorter tire height equals more rpm at cruise.

Taller tire height equals less rpm at cruise.

Many drag racers or track guys will get a taller tire, if they are running out of rpm at the end of the 1/4 mile.

 

[408gt91]

Sounds like 4.10s to me. I cruise at 60 in 5th and its at 2k rpm with 3.73s

+1

 

[blckstng96]

keep in mind the speedo is prob reading incorrectly because there isnt a ford speedo gear for 410s,u would have to pull the trans apart to correct it or get the one that is for dodge i think and it doesnt mesh perfectly,thats the one i got.

 

[87foxstang]

yea...i guess ill just find out this winter for sure, i have a small amount of drippage coming from the rear end and i plan on re sealing it, and then ill just take a peek at the gears lol.

 

[5spd GT]

Just do the test in neutral.

Jack up one tire if you have an open diff, or both tires if you have a working posi or locking differential. Rotate the tire one full revolution for posis and lockers and 2 full revolutions for open diffs. Carefully count the number of full revolutions the driveshaft makes. This is your gear ratio. In other words, if the drive shaft turns 3 ¾ turns, you probably have a 3.73 gear ratio. Turning the tire for twice the number of full revolutions and dividing the drive shaft revolutions by two will give you a more accurate reading.

 

[87foxstang]

whats an open diff, im retarted when it comes to identifying rearends, i have the stock rearend, so would i do 2 rotations?