Speedometer is off

[twobjshelbys]

OK, this is probably covered here but my "tremec speedometer" search didn't yield the answer.

My speedo at 55 is off by 8-9MPH (my handheld GPS had me going 63).

This is a Tremec TKO600 and the Shelby gauge.

I had it up on the lift the other day and didn't think to look at it. I'm guessing this is the gear driven. Does anyone have the magic forumla for the calculation for gear count (or am I looking at getting this adjusted with a computer tuner?)

[blykins]

You use a driven speedometer gear. If you follow the end of your speedometer cable to the transmission, it attaches by one bolt. If you pull that out, there's a little gear on the end of it. You swap that gear to get your speedometer to read right.

Post the rearend ratio of your car, along with the rear tire height, and I'll tell you which gear you need. They're cheap and quick to change.

[wtm442]

http://www.ffcobra.com/FAQ/speedo.html

[dcdoug]

I have a TKO 600 and the white 17 tooth speedometer gear. My speedo reads 4-5mph too slow. Do I need to go down to a 16 tooth or 15 tooth gear (not sure they make a 15 tooth gear). I have read that the speed increase is 2.5-5mph per tooth, depending on which post i read. Does anyone know which is right? Can anyone post a link of which one I need and where to get it?

Thanks!

[SF_SN888KE]

Try:

http://www.fortesparts.com/catalog.cfm?catalogID=2

http://www.fortesparts.com/SpeedoCalculator.htm

[Dangerous Doug]

Mustangs Unlimited has speedometer gears.

www.mustangsunlimited.com

DD

[Argess]

Required Gear teeth = current teeth x indicated speed / actual speed

i.e. If you have 8 teeth now, 8 x 55/63 = 7

hmmm....I made up that formula in my head, ..... is it right?

Anyway,, don't trust your GPS UNLESS you do a test in both directions. GPS has come a long way, but quite a few years back when I use to test boat speeds, I would take a max speed in both directions due to satellite wander (and wind, current, etc., which isn't applicable to a car) and then settle on the average reading.

[twobjshelbys]

I got my gear from the local Ford dealer. Cost me about $2.50 (including tax). I don't remember now which one I ended up with but the old one was red. The reading is now within police limits. If the speedo is on 25 I'm at about 26. At 60 the GPS says 62. I had one of the local sheriff deputy clock me. We had arranged a hand wave signal when I hit 25 - the town speed limit - and he hit the radar and said I was going about 26 (which matched my GPS.) He offered an "off the record" run on a local county road but the correlation of the GPS to the speedo was so good I told him I'd pass.

[dcdoug]

OK, thanks. I think I found the one I need at Mustangs Unlimited, unless I can buy it locally tomorrow.