Speedo Gear info- for those w/ upgraded gears

[Nicoleb3x3]

For those who need more information on the correct speedometer gear to use after they've upgraded rearend gears, I've researched and wrote up a how-to with some useful info:

http://www.gotstang.com/howtos.php?howtoid=4#jump

I needed to do this since I kept my 4 cyl 7.5 rearend w/ 3.73 gears and my speedometer was something like 30% fast!

I just wrote this up for help others who are guessing on what the right speedo gear is for their application.

[5.0literriceeater]

Didnt you buy a wrecked donor car? How come you decided to stay with the 7.5?

[crimsonblack]

Also, if your running the 5.0 automatic with the 8.8 rear end and upgrade to 3.55:1 rear gears you do NOT have to update the speedo. The gear is the same.

I think the donor rear end is what Nicole is getting ready to install.

[Nicoleb3x3]

yes, i have an 8.8 rear -BUT, it needs to be cleaned up, and I want to do the gears and disk conversion before I even bother putting it in. ...and that is money I don't have this season. So I'm going to keep the 7.5 in the mean time (why not it has 3.75 gears in it and the 8.8 likely has 3.08's being it came from an auto)

I WANT to go w/ teh 8.8 w/ 3.55 gears; and I'll still need the same speedo gear I bought (especially in the 90-93 year range the speedo will be off even in that config. The gear I'm getting covers both the 3.55 and 3.75 gears; but w/ the 3.75 I'll never get the speedo to be 100% accurate (it can be done in auto's prior to 1990. -this is another reason why I'll choose the 3.55 in the long run; not to mention my rpms are 2800 or so when going 70 mph right now that kinda sucks since I like to drive 80-90 most of the time I'm on the highway...it's hard to tell what my rpms are when I'm going that fast- since my speedo says I'm going over a 100 mph. Bottom line is my rpms are higher than they should be at lower speeds.

so...I'm fixing the speedo gear so I can just run the 7.5 w/ 3.73 gears for a while and have a better idea how fast I'm going. Any the rpms are a bit higher until I get 3.55 gears.

ps: 8.8 w/ 3.08 auto tranny = hard to cherp the tires
7.5 w/ 3.75 auto tranny = easy to burn the tires
....this is likely why 5.0 swap's people bust the rearends so easily since the 4cyl cars had bigger gears and a weaker rearend. I'm kinda easy on my car compared to most, so I'm sure it'll last until next season when I can build up the 8.8 right