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Junior Charter Member
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354 Posts
Discussion Starter · #1 ·
someone put 3.73 gears in my 8.8 with t-5 and the speedo reads way high. went to switch gear to red speedo gear(21 tooth) but thats whats in it. Any ideas?? anyone change the driving gear in the t-5??
 

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Junior Charter Member
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148 Posts
Do a google and you will find guidelines. A handheld GPS will give your accurate speed.

Say you are reading 10% fast, you need 10% more teeth on the gear to slow down the speedo head, or in your case, a 23 tooth gear.
 

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Premium Member
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9,698 Posts
I've changed the drive gear. The trans has to come out of the car, and the tailshaft housing has to be removed. The most difficult part of the whole procedure is getting the shifter rod lined up when it all goes back together. There are detailed instructions somewhere on the web. The Ford Motorsport catalog has a chart that will tell you what drive and driven gear you will need. Don't use the aftermarket 23 tooth driven gear, it won't last. John
 

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Slacker Extraordinaire
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Whats the drive gear? 6, 7, or 8? What Tires? They all factor in. The drivgear in my t5 should have been a 7 according to the manual but it was a 6.
 

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Charter Member
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With 3:73 and T-5 you'll never get the gears to read MPH accurately, go to an electric speedometer. I had the same set-up as you installed electric speedometer and speed is dead on. Do search this was discussed last week.
 

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Junior Charter Member
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Discussion Starter · #6 ·
thanks.. I'm finding lots of info with a bit of searching. I'm always open to ideas though. So far sounds like an electric speedo may be the way to go
 

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FFCobra Fanatic
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12,975 Posts
Snake I have the same set up as you. Even if you change the internal drive gear in the tranny and use the red 21 tooth driven gear it will still be slightly off too the high side. Trying to use the 23 tooth gear with the stock drive gear will still be inaccurate and yes,it wears out quickly. I am swapping over to a electric speedo for this reason. If staying mach. speedo internal gear change and 21 driven will be close,but not perfect. Off by 5% when done.That is what I have now.
 

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FFCobra Fanatic
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Does AutoMeter make an electric speedo that is the same size as the mechanical guage?
 

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Senior Member
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8,356 Posts
First try a 23 gear, I think it is white. I've heard the due have a tendency to strip, though. Worked fine in my 3.55/T5 combo until I toasted the speedo cable on the headers. Still have to put the new one in.
 

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Senior Charter Member
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1,168 Posts
I'm also interested in an Autometer classic Speedo that takes electronic input. I can hook to the TKO tranny electrical out. I looked in the Autometer web site and couldn't find the right speedo. Anyone have luck?
Pete
 

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Premium Member
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9,698 Posts
The 23t gear is a Jeep part. It has the wrong pitch to mate correctly with the Ford drive gear. It will work - for awhile, but will start shedding teeth sooner or later. I don't know what harm can be done to the inside of the gearbox with a bunch of plastic gear teeth floating around, but I imagine they could plug some of the lube orifices at the least.

This is the Hanlon Motorsport speedo site, plug in your tire size and rear gear, and it will tell you what drive and driven gear you need.
http://www.hanlonmotorsports.com/t5speedo.asp
 

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Senior Charter Member
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1,168 Posts
I found the Electronic Autometer Traditional Speedo that matches the Traditional Gauge set sold by FRR. It's listed on the Autometer web site under P/N 2489. $179.88 at Summit. It will take any sensor input from 500 to 400,000 pulses per mile. They list a calibration procedure in the instructions. Your speedo will be as accurate as the 2 mile stretch of road you use to do the calibration.

Autometer Web site Tradional Speedometer 2489
Autometer Traditional Speedometer 2489 at Summit

If you don't have an electronic speed sensor build into your transmission, then you can install the Autometer hall sensor in the speedo cable connection on the transmission and get a compatable signal for the electronic speedo.

Autometer Hall speed sensor for converting mechanical to electronic


The TKO has both mechanical cable connection and electronic speed output. If you use the electric connection, you need to get a special plug to cover the mechanical connection. Forte sells this plug. Don't use the rubber plug that comes in the tranny new.

Forte's Tremec Mechanical Speedo plug

Looks like I have a Summit order in my to-do list for today and my mechanical gauge, cable and gears go up for sale.

Pete
 
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