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Topic: Speedo still off after speedo gear change (Read 2500 times) previous topic - next topic

Speedo still off after speedo gear change

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?
[SIGPIC][/SIGPIC]http://www.fquick.com/slicksport88
88 Sport - 5.0HO, Mass Air, A9L, 73mm C&L meter, BBK CAI, 255 lph pump, 1.7 roller rockers,Professional Products damper, Chuck W motor mounts, BBK shorties & H-pipe, Flowmaster 40 series, 8.8 rear w/3.27's, 93 Cobra M/C, BAER 13in. drilled/slotted rotors front and back, cobra calipers, Russell braided brake lines front & back, C/C plates, 03cobra rims, 255/40/17 Nitto 555's all around

Re: Speedo still off after speedo gear change

Reply #1 –
theres only so close youre going to get it on 80's electronics, and on a tire size that wasnt available on these cars
It's Gumby's fault.

Re: Speedo still off after speedo gear change

Reply #2 –
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...

Re: Speedo still off after speedo gear change

Reply #3 –
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.
[SIGPIC][/SIGPIC]http://www.fquick.com/slicksport88
88 Sport - 5.0HO, Mass Air, A9L, 73mm C&L meter, BBK CAI, 255 lph pump, 1.7 roller rockers,Professional Products damper, Chuck W motor mounts, BBK shorties & H-pipe, Flowmaster 40 series, 8.8 rear w/3.27's, 93 Cobra M/C, BAER 13in. drilled/slotted rotors front and back, cobra calipers, Russell braided brake lines front & back, C/C plates, 03cobra rims, 255/40/17 Nitto 555's all around

Re: Speedo still off after speedo gear change

Reply #4 –
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.

Re: Speedo still off after speedo gear change

Reply #5 –
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.
Quote from: jcassity
I honestly dont think you could exceed the cost of a new car buy installing new *stock* parts everywhere in your coug our tbird. Its just plain impossible. You could revamp the entire drivetrain/engine/suspenstion and still come out ahead.
Hooligans! 
1988 Crown Vic wagon. 120K California car. Wifes grocery getter. (junked)
1987 Ford Thunderbird LX. 5.0. s.o., sn-95 t-5 and an f-150 clutch. Driven daily and going strong.
1986 cougar.
lilsammywasapunkrocker@yahoo.com

Re: Speedo still off after speedo gear change

Reply #6 –
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.
[SIGPIC][/SIGPIC]http://www.fquick.com/slicksport88
88 Sport - 5.0HO, Mass Air, A9L, 73mm C&L meter, BBK CAI, 255 lph pump, 1.7 roller rockers,Professional Products damper, Chuck W motor mounts, BBK shorties & H-pipe, Flowmaster 40 series, 8.8 rear w/3.27's, 93 Cobra M/C, BAER 13in. drilled/slotted rotors front and back, cobra calipers, Russell braided brake lines front & back, C/C plates, 03cobra rims, 255/40/17 Nitto 555's all around
 

Re: Speedo still off after speedo gear change

Reply #7 –
Quote from: slicksport88
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...