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when changing rear gears(3.55 to 3.73) do I just need to change the speedo gear or does the computer need reflashing for the correct speedo reading. Truck is a '98 5.4 2wd with an open 9.75 diff.
Welcome to FTE
You can fix the speedo with a tune to the computer.
I would recommend going to a 4.10 gear. Going from 3.55 to 3.37 you wont hardly be able to tell the difference.
I went from 3.55 to 4.10s and added a L/S diff at the same time to save some money later and I love my 4.10s!
I agree. You wont hardly be able to notice a difference between 3.55 and 3.73's. Since your truck is a pre-'99, your speedometer is measured by a gear in the tailshaft of the transmission. You will need a new gear with the correct ammount of teeth.
I'm planning the same, but 3.55 to 4.10 with LS. I was told a while back to fix the speedo I would need to change a small gear in the top of the tranny where the cable goes in. I have a E4OD tranny.
thanks for the info. I'd like to put steeper gears in but here in Canada gas is over $4.00 a gallon and i'd like to keep some kind of gas mileage, since we take the highway into town.I've also got 2 mustangs one 3.55 gears and the other 4.10(both 5.0 cars),and I like the 4.10 gear car better.