4:10's installed - speedo off?

marvinmycat · Feb 13, 2004

I just swapped out my stock gears for 4:10's on my 1998 Mustang 3.8L V6 AODE. I also installed a 23 tooth speedo gear, but I don't think that the speedometer is reading correctly. Should I have installed a different speedo gear other than the 23 tooth one, or do I have to also get something else installed as well? Remember this is on an automatic with 4:10's now.

I haven't had a chance to get someone to pace me yet, and it is Friday and everyone drives like a maniac, so I just feel like my speedometer is way off.

Thanks for any info.

Jamez · Feb 13, 2004

According to Steeda you have the right gear. I got mine from them and seem to be just about right, if not dead on. How's the gears so far?

marvinmycat · Feb 13, 2004

Actually, they are kind of wierd. I didn't realize how much of a difference they would make and how different the car actually responds in the way of the tranny shifting. One thing I did notice, that is - if the speedo is actually correct, is that the car accelerates MUCH quicker!

Was at a stop light and the guy in the left lane was playing games by nudging ahead while the light was red. Even though there were no signs indicating the two lane road became a one lane road across the other side of the intersection, I decided to punch it anyway as the light went green. I was already doing 40mph by the time I got across the intersection and had to let off the gas before I redlined. I didn't expect that one at all. Oh yea, I beat him out for position, EASY.

According to GEFRacing, the 23 tooth speedcal is for both the 3:73 and 4:10 gear sets, while 50resto says the 23 tooth is for 4:10's and the 21 tooth is for 3:73's. I'm certain I got the 23 tooth one as that's what was stamped on the package when it came. I just can't believe that the car is now that much quicker acceleration wise!

GREENBIOCH · Feb 13, 2004

I know gears kick ass...When I got my 3.73's I put the 23 tooth speedo in my 98 it seems to read right. Actually I think it reads slightly faster then what I'm doing I can tell when photo radar is around and people slow down, i tend to be going a bit faster on my speedo than the speed limit.

I just checked Steeda's website and they say 23 tooth as well for your car with 4.10's.

I love the acceleration difference. Don't fear the gear.

zoopa_man · Feb 13, 2004

I'm curious to know how much of a gas mileage difference you've gotten. Everyone is always asking and I read a different response from people each time. Let us know after you get to drive around for a little while. I'm still split between 3.73's or 4.10's for my auto. I do a lot of highway and my car's an every day driver. I'd love the acceleration from the higher gear but don't need the headache of bad gas mileage. Fill us in on how much of a difference you see in MPG. I'm curious to know.

marvinmycat · Feb 14, 2004

Just got paced, and the speedo reads 5mph faster than actual at 65mph. I guess the 23 tooth speedcal makes the speedometer less inaccurate then.

Time to rip apart the gauge pod again I guess.

Jamez · Feb 14, 2004

If I'm not mistaken your speedo gear goes on the speed sensor that is bolted to the tranny, not in the guage cluster.

marvinmycat · Feb 14, 2004

You're right, it does go on the tranny tail. But in order to fix the difference in speedo/real mph, I'll have to play with my speedo needle to get it right.

2002CherryRedV6 · Feb 14, 2004

dumb question:

do i have to do a ecu correction or can i just get the speed sensor gear corrector ring for the differential???

reason i ask is beacuse i have a 2002, unlike the 98 in the begining of this thread....

thanks

zoopa_man · Feb 14, 2004

2002CherryRedV6 said:
dumb question:

do i have to do a ecu correction or can i just get the speed sensor gear corrector ring for the differential???

reason i ask is beacuse i have a 2002, unlike the 98 in the begining of this thread....

thanks

For the 99 and newer cars you have to get a chip to correct for the speed.

2002CherryRedV6 · Feb 14, 2004

thats what i thought, thanks!!!!!

SpectorV · Feb 14, 2004

there is nothing that you can do to correct the speedo, live with it.

marvinmycat · Feb 14, 2004

SpectorV said:
there is nothing that you can do to correct the speedo, live with it.

Like I said earlier, if that's the closest the speedcal can get the speedo, then I'll have to reposition the needle at 65mph so I DON'T have to live with it.

atreyu · Feb 14, 2004

http://www.dallasmustang.com/index....gory_Code=L_Drivetrain_SpeedometerAccessories

Dallas Mustang sells a electronic speedo calibraitor its more than likely your best bet for a accurate speedo reading

zoopa_man · Feb 14, 2004

Wow 100 seems awful steep. Wouldn't that money be better spent towards a whole new ECU ??? The whole point in doing just a speedo gear would be to save money. So if your going to drop a hundred bucks on a speedo chip you might as well add some more money to it and get the benefits of a new ECU. A hundred bucks just seems like a lot to spend just to fix the speed. At least with a new ECU you can do upgraded transmission shift points for the new gears, advance your timing a bit, burn a higher octane fuel...and all the other things you can do with a programmed ECU.

In my opinion your better off living with what you have until you need a new ECU to accommodate other upgrades. Drive with traffic like you should anyway and don't be reckless with your speed.

SpectorV · Feb 15, 2004

i have a dallas speed cal and it works great but its for manual only, you can move your needed to a given mph but you WILL still live with teh odometer readings being to fast.

marvinmycat · Feb 15, 2004

The site says that the speedcal will work with 94-98 automatics as well.

On a side note, I just did my first two-wheel burnout today!

SpectorV · Feb 15, 2004

interesting if it works for autos then thats great, i have just alwasy heard it does not, dont really know why it wouldnt but oh well. Make sure you soder the connection very good mine came loose and my speedo/odometer stoped working one evening i freaked but i turned around nd went home and checked and when i sodered it together (power wire for the speed cal) it worked fine.

marvinmycat · Feb 17, 2004

OK, I called around everywhere trying to get some help on this, but even the dealer couldn't help me. Funny how when I pulled my gauges last time, a dealer in another city had the machine to hook up to the instrument cluster to get the correct reading for a 94-98.

So, I finally decided to just do the math and figure it out from there. Since I had 3.27's and went to 4.10's, I just ratio'd the thing.

3.27 @ 65mph = 1950 rpm.
4.10 @ 65mph = 2444 rpm.

I then figured out what the rpm's should be from 30 to 65 mph in 5 mph incrments, then went for a ride with the face plate removed. I later confirmed my speedo setting by going through a speed trap. I wish there was a funny story here, but sorry. I actually pulled up to the three cops sitting in a parking lot and they had me drive past their trap vehicle. I was two miles and hour over my actual speed. Not bad. I fixed this later on by going 52, and lowering the needle back to 50.

Side note. While talking to the know-it-all officer, he informed me that the factory speedo's have an allowable error of margin of 2%, while the radar guns the police use can have an acceptable error margin of 3%. The police man also informed me that I didn't need to change my needle setting with the switching of my gear ratio, and he procedded to tell me why. I didn't argue with him, I just told him that when a friend paced me I was 5 mph over my actual speed with the speedo recal gear installed. He still didn't listen, so I thanked him and went on my merry way before he decided to shake me down!

So, for all us 94-98 people, use the ratio of your gears, mph, and rpm to help set your needle.

65mph:

ratio rpm
3.27 1950
----=----
4.10 ????

Cross multiply. 4.10's @ 65mph = 2444rpm.

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