pk222

hey guys recently I did a clutch swap on my 89 mustang and when I took out the speedo cable I checked the speedo gear and its red, I might be wrong but I think that the red speedo gear is for 3.73 gears also my speedo is a little off saying I'm going about 5 to sometimes 10 mph slower than I am depending on speed. I was told that I had the optional 3.08 gears by the previous owner. from the speedo gear I have and the amount my speedo is off does anyone know what gear I have? I dont think I have 3.73s because my gearing isn't that short but I dont know much because I haven't driven any other fox body mustangs.
when I'm doing 80 in 5th gear I'm at around 1800-2000 rpm with someone following me whos speedometer is correct
the speedo could also be off because of my tires not being caliberated to the speedo, the tires are 235/45/17 if anyone knows.
I don't know if I'm right about the speedo gear or not but I thought I might as well try to find out what I really have because I was planning on possibly swapping in 3.73 gears.

PRO50SC

Well maybe some idiot put a replacement gear in that didn't know what he was doing.

Jack the car up. Put a mark on the tire and one on the yoke of the driveshaft. Rotate the tire one revolution. Count how many times the driveshaft goes around. That will tell you what gears you have. Example, 3.5 times=3.55's. Understand?

mjr46

just pull the rear end cover and count teeth on ring and pinion and divide the two numbers

PRO50SC

I think my way is just a tad bit easier there pal!

ACE

^^agreed and you dont have to play with gear oil on this wonderful hot day[:@]

stang8689

Its real easy, just do it twice to double check

pk222

hey guys, sorry it took me so long to post back about this and I know I'm probably going to get shot down for bringing up an old post but for some reason I couldn't find this post until now but I will try it and see how it goes. I will post back tomarrow after I try this.

mjr46

may be so^^^BUT TIRE SIZE CAN AFFECT result and produce an inaccurate result

pk222

I see what your saying mjr46.
do you know if it would make a big enough difference to not be able to tell that way with 235/45/17 tires?

nitrous_bob

no it won't, you'll get the count close enuff. and if it is in between go w/ the smaller gearset (numerically smaller)

for stock gearing look at the tag in the door under "ax" m=2.73 and z=3.08

by your rpms, you have more like 3.08

your '89 trans has a 7t drive gear in it, and yes, a 21t driven would be correct for 3.73's

to give you an idea, i am off 5-10 mph at hiway speed (looks like i'm going faster) and i am2 driven gear teeth off , i just never swapped the easy one

my guess, they had 3.73, corrected it, then swapped 3.08 back in b4 it sold. it would only be worth it if you had it done for free since labor for a gearswap is more than the gearset itself

you'll need yellow for 3.08 and wine for 2.73