I just recently had a new Eaton posi unit and 3:73's installed in my 10 bolt rear for my 93 Z28. I originally had 2:73's, stock from the factory, in the car. After the install my speedo was way off, and still is. The slower I'm driving, the less it is off. Around town, at about 35 - 40 MPH I'm reading around 40 - 45MPH. Around 65 - 70 MPH I'm reading more like 80-85+MPH. It has been adjusted but is still off. That isn't my main concern though b/c I know that can be fixed. The bigger problem is that now, after the install, my stock tachometer does not read tru at all. At about 2200 RPM the guage starts bouncing and I cannot tell what RPM I am at. I was wondering if anyone knew what may cause that because my tranmission shop, where the rear end was done, well they say that my RPM guage bouncing and acting funny DOES NOT have anything to do with the new posi and new gears that they installed. I'm a little suspicious about how true that is b/c my car was fine before the work was done on the rear. If anyone has any ideas please let me know so I can try and pinpoint the problem. Also, when I'm driving, even though the RPM needle goes wild, my engine is consistent, so what I'm trying to say is that the engine does not sound like the needle is showing.

Thanks, Giovanni

 

The speedometer can be corrected easily. The drive gear for your speedometer will be a 15 tooth, and the driven gear between 43 & 45, depending on tire height. The tachometer being off has nothing to do with the rear end gear ratio, the tach "reads" engine rpm only.

 

gotcha - yea i figured the speedo wasnt a big issue - he was adding teeth to it er something along those lines and it corrected somewhat but it is still off - and yea the RPM guage, well it does make sense that it wouldnt affect the motor.....i just had my car checked and found out i have an oil leak coming from somewhere near my timing chain cover.....which was totally redone in april...so it's warrantied still....i assume that if i get enough oil on my stupid opti that i can get bad signals from that, since my one mech did say my opti was pretty wet...and having gone thru 3 opti's so far, i kno how any liquid will screw the opti......thanks for replying...do you happen to kno of anywhere where i can get the opti conversion to coild packs for LT-1.....that is seeming like a better idea everyday if i can pull that conversion off?


THANKS

Giovanni