How does a person with 4.56's and an AOD end up with a calibrated speedo?
 

I'm trying to set up for my 4.56 install to give my AOD that real pep it needs. Apparently, the calculators tell me I need a 28 tooth or something like that! I'm running 225/60/16's and currently I have a 21 tooth driven gear with my 3.73's (I think that means I have the 8 tooth inside). Now, I've seen 23 toothers out there but thats about it.

What can I possibly do? I know they have electronic correction devices but it seems like overkill. I also know that the drive gear is part of the output shaft. Does ford make recalibrated speedo innards? I want to keep the stock speedo gauge.

Sorry I am inundating the board with messages but I am really tearing my car to bits and changing everything at the moment and I'm in the murky and less explorered area of automatic performance....anyhow!

"Don" at transmissioncenter.net writes me that I can

"I assume this is a cable driver speedometer. If you use a 7 tooth output shaft with a 23 tooth driven gear this will get it reading 52 MPH at a true 50 MPH."

I remember from my rebuild that the output shaft is the one thing that really didnt want to come out. I would have to tear apart the transmission to switch the output shaft, wouldnt I? I cant just pop it off with the tailshaft cover removed, can I?

Your combo does not require that steep of a gear. The only time I see people running that much gear is in a N/A trim only...and shifting over 6800 rpms.

The gear you have now is perfect! Get a GOOD converter and spray it with a 125-150 shot. It will give you that help out of the hole you are looking for!:D

Here's how I chose the gear:

My original 1987 ford mustang lx 5.0 pulled about 3000 rpms going 75 on 25.5 inch tires (r15's). I later found out that I had been driving around on 3.73's for years and didnt even know it. I just figured 5.0's were all high revvers till I rode in a 2.73 equipped stang and saw how low that dudes rpm's were! I liked that rpm band for highway cruising and wanted my highway umph back. When you stabbed the throttle, you were already in the power band and the car just took off! Right now, even with 3.73's, she churges around at 2000 rpms at 60 and really just fights the gear all the way up to 75 mph when it is at a measly 2400.

Sooooo...

I hit a few calculators.

http://www.4x4cyberstore.com/website/rpmchart.html

With my aod.s .67 OD and my taller 26.6 tires (r16's), I ended up with the 4.56's at the end of the equation.

I patted myself on the back for being _that_ hardcore and walked around feeling hairy chested the rest of the day =P. Alas, I already have the gears, they are sitting in my room. They look sexy! 41 teeth on the ring and 9 teeth on the pinion.

My long term goals are to make the car fast on 'all motor'. I'm not a big fan of spray. It's a consumable resource. It's not really......like......part of the motor, you're just spraying liquid air into your motor to make it work harder. Have you seen how much tubing it takes to set up a good nitruous system. GASP! I spent months cleaning up my enginebay. Longterm, I'm going to add a 3000 stall and some twisted wedge heads and then call the car complete.

What's "N/A trim only", by the way?

N/A =normally asparited ==no power adder like a turbo or super charger.
If you want a bad ass converter..look for a stall thats about 1,500-2,000 rpms below shift point. (Thats for more of a hard core strret/strip set-up)
So if you shift at lets say 6,000 rpms your going to want a 4,000 stall.
I know,I know way to much for a street car.... I run 4,800 on my street car.:p :D
If you like to play on the hwy and stuff like that, look for a 3200-3600 stall for a "4.56 geared" mustang with your engine combo. (This is where alot of people mess up and don't look into the proper converter applications.;)
And then you will need to do some work to your engine combo to make power in the upper rpm range so it all sings together.
And don't pay any attention to below 2500rpms.

Another piece of advice is to actually measure the circumference of the tire instead of calculating it from the advertised diameter. There can be alot of difference.

To do this, inflate the tire to the normal pressure and measure all the way around the center. I have a tape measure specifically made for doing this.

Take the actual circumference number and plug that in to the formula. Its a heck of a lot more accurate this way.

Andy

I have reached the conclusion that, after many many phone calls, replacing the output shaft is the only way to go and I am thoroughly not interested in doing this. I'll go 23 tooth. Is there anything else in terms of kludges that I can do? Maybe increasing the rear tire diameter.

How big of a street radial will fit inside the rear fender wells with motorsport 'c' springs? I might go for that 70's @ss in the air big tires in the back look....big tires = better gas milage.