Ok this is my problem. I finished the cobra brake upgrade along with the 8.8 disk rear change as well on my 88 Sport. Im running 03 cobra rims 17x9 w/ 245/45/17 all around. So far so good. I called the Ford Racing Tech for advice on what speedo gear to change to. The data plate on the rear says 3.27 (old gears were 2.73) so he recommended a 19 tooth gear. Well im running down the highway to check it against the speed check thingy and im showing 5mph faster on the speedo than whats displayed on radar. I know....not a whole lot but is there anyway to get closer to being dead on?
theres only so close youre going to get it on 80's electronics, and on a tire size that wasnt available on these cars
Each tooth added(or subtracted) to the driven gear will change speedo reading approx 3mph... Go to a 20 tooth and it should be just a couple mph fast... FYI a 21 is as many teeth as Ford sells, but I thinkin you're gonna start reading slow with that one...
Thanks for the info....I'll pick one up from Latemodel Restoration tomorrow and see what happens. Also another thought occured to me. The rear end I purchased was used but in good shape...im wondering if the previous owner ditched the 3.27's and threw in something else, maybe 3.55's? But I don't know what impact or I should say difference in speedo reading that would make. Just a thought.
I say you need a 21 tooth.
With my last bird it had 2.73s and i switched to 3.27s.
The drive gear in the t-bird/coug aod is an 8 tooth drive therefore 21 tooth is right on the money.
you could always play with your tire size alittle. That will get you another 1 or 2 mph diffrence and shouldnt change a whole lot.
Purchased a 21 tooth speedo gear today and threw it in. Took her out on the highway to check it and now im only showing 2mph faster than actual. Guess that's as close as im gonna get with this one.
Thats at least as good as factory.... Few (if any) of these were dead on when new...