Question. The speedo gear I installed is the orange speedo gear used for 3.27 and 3.55 rear ends.

Now my speedometer reads 5mph high.

I know I did the cluster swap while retaining the odometer but I was able to recalibrate it pretty much 100% using the "remove speedo needle, reinstall, use GPS to verify actual MPH" method.

Prior my speedo read about 2mph fast. Although it always seemed to read a little fast, even before I did the cluster swap.

Now given that I changed the speedometer gear in the transmission tailshaft to the correct gear for my gears and did not mess with the gauge cluster/speedometer gauge for months, shouldnt it still read about 2mph fast? But now it reads about 5mph fast.....using my Garmin GPS to verify my actual speed.

Any ideas?

Do you have the stock tire size still?

Yes. Not the stock tires (which maybe contributed to the slight difference in actual speed?) but stock store size...you know how all tires aren't exactly the same dimensions.

But this extra difference in inaccurate speed (another 3 or so mph off added) after the gear swap and speedo gear swap has me wondering.

If the speedo gear is used for both the 3.27 and 3.55 gear sets it isn't going to be 100% accurate either way. I'm going to assume it's related to that.

Perhaps but how could it be that innacurate off of the lot if it even says "certified calibration" on the speedometer? Meaning that it has to be pretty close to dead on actual speed.....so they can pace other cars without using radar to trip the radar detectors and still issue speeding tickets.....

By the way, the vehicle I got the speedo gear from (not the same car I pulled the gears from) also had 3.55's.....I just looked at this chart later which listed the "orange" speedo gear for 3.27 and 3.55 ratios...

http://www.moldyrabbit.com/liquid/speedo_gear.html

it's not certified because you've put it in a different car with a different setup. just because it says it on the dash doesn't make it so.

as far as the inaccuracy, how can one speedo gear be accurate for both 3.27 and 3.55 gears? with 3.27s the driveshaft will spin a rpm x at 70 mph while the same driveshaft with 3.55s will spin a different speed at the same vehicle speed. That speedo gear you put in will either be accurate with 3.27s, accurate with 3.55s or accurate somewhere in between. It can't be accurate for both. If that's what you put in for a speedo gear it shouldn't read the same as what you used to have for a setup.

You know what, it is possible that my transmission has 8 drive teeth instead of 7. In which case, with a 3.55 gear, it would call for the black 23 teeth gear....not the orange 20 teeth gear.

That would "slow" the speed with the extra teeth. That might make sense why it is showing so much extra. If it goes back to the original ~2mph accuracy I'll be happy, but 5-6 mph inaccuracy is rather annoying!

I'll call Ford tomorrow and see how much this black gear is.....it's actually from Mustang's with manual transmissions but I never see any of those in the junkyards so it wouldn't be really easy or even possible to find one used....oh well.

It seems like I might need that black gear, but it sounds like the black gear is only available online. Appears that Ford only sells a white gear which is shorter (same tooth count of 23) for manual transmissions that seems to crack easy or something, according to the Moldy Rabbit site.

My speedo runs about 8% too slow with the 8 tooth output shaft gear and the black driven gear.

That works out to running at indicated 60 mph but actually going about 65

The Purple 21 tooth gear would be a better choice

You're running 3.55's too?

Interesting that yours shows exactly the opposite, 5mph too slow.

I was searching and found another thread (I revived it since it last had activity in February) speaking about these speedometer gears for our 8 tooth output shaft.

Nevermind, I see you are running 3.55's. That's odd, the other thread made it sound like the 23 teeth black gear was the definite way to go for 3.55's and an 8 tooth output shaft.

The actual tires you run will have a big effect. With my 225/60/16 snow tires I was still about 4% slow. Mounting the 235/55/17's drove the error up to 8% slow.

I would rather have the speedo a bit fast vs too slow

Oh well, I am currently running the stock 225 60 R16's and don't plan to change that anytime in the near future....

So it still sounds like the purple 21 tooth gear would be a better choice than the 23 tooth custom black gear?

I can go to Ford on Monday and see if they accept returns just incase it isn't the right part. I am guessing they charge some sort of restocking fee.

Yes, I'd rather have my speedo read too fast than too slow. I was fine with it reading 1-2mph fast previously, but reading 5-6 fast (like it is now using the incorrect orange 20 teeth gear) is a bit annoying and quite a big difference.

PS, I am loving the 3.55's and the trac-lok. I actually seem to be using less fuel now given a certain distance (not paying attention to the odometer really since it is incorrect at the moment) than I was before with the nasty 2.73's. And the limited slip is a giant plus as well. Awesome! This is how they all should have come stock, suspension wise too......nasty ultra soft civilian coils. Yuck!