How to: T45 transmission speedo gear swap

AaRoN · May 7, 2008

I recently had 4.10's installed. So, obviously, the speedometer is off. The stock speedo gear in my 98 GT is an 18 tooth gear designed for 2.73's. I purchased a 23 tooth speedo gear when I got my 4.10's.
NOTE: As always, use caution when working on your car. This board cannot be held responsible for any harm you cause or is caused to you by following this write-up.

Tools needed:
New speedo gear (whichever suits your situation)
Jack
Jack stands
12mm socket
Ratchet (of course)
Long extension (this made things much easier)
Regular (straight edge) screwdriver

Located on the driver's side of the transmission, on the tailshaft is the bolt that we're looking for.
It's a 12mm and there's only 1. Get that out and then unclip the harness that is attached.

Once the bolt and harness are removed you can get the plug holding the speedo gear out. Just pull straight down. You may have to turn it slightly and then pull it out just to loosen it.
(I don't know why the color was so crappy in this pic. Oh well, you get the idea.)

Here's what the speedo gear will look like once it's out:

Next to the new speedo gear:

There is a c-clip holding the speed gear onto the plug. This is where your regular (straight edged) screwdriver comes into play. Use it to carefully pry it off.

Installion, obviously, is reverse of removal. Make sure to use the c-clip you just took out to hold the new speedo gear onto the plug.

After installing, my speedo is actually ALOT closer than I thought it would be. It's within 5mph.

SRT Handz · May 16, 2008

why did you choose to change the speedo gear instead of using a Speed Cal?

Javi · May 16, 2008

Great write up Aaron :thumb:

AaRoN · May 16, 2008

SRT Handz said:
why did you choose to change the speedo gear instead of using a Speed Cal?

Because I haven't bought a speedcal yet :dunno:

SRT Handz · May 17, 2008

So if you have gears and want the speedo corrected do you have to get a speedcal & the Trans Gear or One or the other?

ju015dd · May 19, 2008

one or the other, but the gear is wayyyyy cheaper.

AaRoN · May 24, 2008

ju015dd said:
one or the other, but the gear is wayyyyy cheaper.

Yup. It's about a 1/5th of the price of the speedcal.

chromeyellow · Jun 13, 2008

nice writeup, thanks

sleepn_sn95 · Nov 20, 2008

is the same process for 94-95's

97aztecgt · Nov 20, 2008

Where can you get the new speedo gear?

Brenton

vermilion · Nov 21, 2008

upr has them or blue oval industries has them on ebay. i advise the white gear oppsed the red one. material issues.

duff daddy · Apr 28, 2009

im just gonna add that if you get an x-cal and you expect to change your pinion factor (for gears say a 3.27 to 373's) you will be SOL the x/cal only works for 99+ cars ie electronic pick up.. kinda an ovbious thing but just incase someone was wondering ...

AaRoN · May 26, 2009

duff daddy said:
im just gonna add that if you get an x-cal and you expect to change your pinion factor (for gears say a 3.27 to 373's) you will be SOL the x/cal only works for 99+ cars ie electronic pick up.. kinda an ovbious thing but just incase someone was wondering ...

No, actually you can get a speed cal from Dallas Mustang that works on our cars.