TechCam97

iTrader: (5)

My 1993 Trans Am with a 4L60 has 3.73 rear gears in it (took diff cover off, counted and confirmed), it has 275/40/17 rear tires (25.7 diameter), a 15 tooth drive gear installed, and the factory 44 tooth driven gear. From all my calculations it should be correct, but my speedometer still reads about 7mph too fast (reads 77mph, but going 70mph via gps). Not quite sure what else to look for so any advice would be appreciated!

lt1-xjs

You should run 2400 rpm @ 70 mph with a 3:73 gear. Running 77 mph @ 2400 rpm is a 3:42 gear.

TechCam97

iTrader: (5)

It runs at 2400 rpm reading 70 mph on my gps, but the speedometer reads 7mph faster. When I had the rear diff cover off a few days ago I counted the teeth to make sure it had 3.73s, so I know that's correct. I swapped out the drive gear on the trans to a 15 tooth from the factory 17 tooth and I have the correct 44 tooth driven gear installed. According to every source I've referenced I should be good to go, but my speedo is still off. Definitely confusing.....

FirstYrLS1Z

iTrader: (4)

Do you really expect the speedo to be accurate. I've seen that much of a discrepancy on unaltered f-bods.

TechCam97

iTrader: (5)

I've been driving fourth gens for almost two decades and this is the only one that has been this far off. All my others (six in total) have been within 3mph. Hell, my 67 is dead on.