Quick Speedo gear solution
 

Hi guys!!
I recently swapped an old original 3 speed automatic transmission from my 68 mustang and replaced it with a T5 with a 3.35 first gear. I also replaced my 2.79 final ratio for a 3.55 but at one point I should ve checked how all of this would affect my speedo....but I didnt. As a result as you probably figured out, my original miles per hour speed gauge is actually in Km/h. 30 on the gauge is about 32km/h in real life. I have no idea which gear Im suposed to use and I have till the end of today to place an order in which Id like to include the proper gear. Does anyone have an idea how many teeth the new one needs to have to bring back my gauge to read actual miles per hour?? Just in case it matters, I still have a 289 and I have 205 60R15 tires on.

Thanks for looking and have a great one!!
FRank :)

I believe I went with the pink speedo gear (19 tooth) with my old 5.0L with t-5, and 3.55's. The pink gear is good for all t-5's from '83 to '89 factory or world class spec t-5's. Now if you have the '90 plus t-5 then you'll will need the red gear (21 tooth). Basically due to the 5th gear ratio. That's what will determine wich one you will need. So hopefully you know what t-5 you have.

There is a calculation that you have to do to get the correct gear, anything else is just a guess.
Try this,
https://lmr.com/products/Mustang-Spe...ear-Calculator

Hey thx for the help guys. Im gonna do my homework then and get it right. I think my T5 is pre 80s, like 73 or 74. I had a good friend help me with this caus I really didnt know much about picking and rebuilding an old T5. He told me all about it but some info I forgot. It is a world class though, that much I know. Ill let you know the results. Thanks again!! :)

I can't help with the speedo gear, but here is a little background info on the T5 from the people who built mine. This will help tell the difference between a world class and non-WC transmission, and clarify years of availability.

T5 History in Ford Mustangs with specifications for World class and non-World class T5's Modern Driveline

T5 tranny didn't come out until the early 1980s, Ford first used them in mid-1983 model year on the Mustangs and Capris.

Yeah I realized my guess about the date of my transmission's production was wrong when I read Roddy's link about the history of the T5. Im gonna have a few questions to ask my friends. Thanks for the link btw roddy, very useful.

Glad to help.