I have an M28 transmission in my 93 Z28. If I'm interpreting all I've read correctly, a 3:73 rear end in my car would be like 4:10 in everyone elses. Is this OK for a bolt-on car? As it is, I need to figure out what my rear end is. It was replaced several years ago with an axle from a 98 Trans-Am. Also, I'm reading conflicting info on what I need to do to correct the speedo. Right now, it reads about 3-4mph too high. Any clarification would be much appreciated.

 

Well dependign on who you ask, yes your car will feel like a cra with a 4.10 gear b/c of the gearing of the m28. I see no reason why a gear swap wouldnt be beneficial(sp). Othen then take it easy on sticky tires. Also if the rear was takin out of a 98 car it could have several gear. If it came out of a m6 then it has 3.42's, if it came out of an a4 with out the performance gear then it has 3.23's or it also could have 2.73's.

 

Its just "math":

M28 with 3.36 1st gear:

3.36 x 2.73 = 9.173 (stock, overall gear ratio)
3.36 x 3.23 = 10.853
3.36 x 3.42 = 11.491
3.36 x 3.73 = 12.533
3.36 x 4.11 = 13.810

For the M29 with 2.97 1st gear:
2.97 x 3.23 = 9.593 (stock)
2.97 x 3.42 = 10.157
2.97 x 3.73 = 11.078
2.97 x 4.11 = 12.207

For the MN6 with 2.66 1st gear:
2.66 x 3.42 = 9.097 (stock on 94 and up)
2.66 x 3.73 = 9.922
2.66 x 4.11 = 10.933
2.66 x 4.56 = 12.130

So.... an M28 with 3.73's, in first gear, will feel like is geared even lower than a 94+ MN6 with 4.56 gears. To have the equivalent of the 94 and later MN6 with 4.11's, you could run the 3.23's.