So i got a 4th gen differential installed in my car and it has 3.42 gears. The car used to have 2.73 gears, and it drove and shifted fine with those. Now that is has the 3.42s at about 40-55mph it will hunt about 300rpm with normal acceleration, if i put it in 3rd it will be fine, also is fine if i put my foot on the brakes a little. What would cause this?

Also what should i change in the tranny to make it work better with the new gear ratio.

BTw here are some pictures of the 4th gen rear with the 3rd gen wheels

 

anyone??

 

.... are you triggering a code 24 when in 4th gear at those speeds?

 

nope no codes

 

It sounds like your VSS is not reading accurately, effecting lockup, despite no code being intermittently thrown....

 

yeah the speedo reads 3 mph high, but it was 5 lower and it worked fine

 

The problem though is your torque converter lockup, not your speedometer. The ECM is getting a signal from the VSS, but not the proper calibrated signal though, which is why a code 24 isn't being thrown, and your surging back and forth when the TCC is being commanded to lock. You need to either calibrate it correctly, or bypass it entirely....

 

ok. So if i get the 40 tooth speedo gear instead of the 41 tooth gear it should be good, because this started happening when i put in the 41, changing from the 37 tooth gear.

 

Do you need the color code chart for the speedo gears....?

 

No i got all the info for that. In the parts book it said to use the yellow 41 tooth gear with the 3.42 gears. So now i will try the black 40 tooth gear.