2.56 open to 3.42 LSD. Is programming required?

Got a 1995 Caprice wagon. It appears to have the 2.56 with open rear end. Was thinking of going with a used 3.42 LSD from a truck. I know I need the reluctor. How many teeth should that have? Besides an install kit with the axle and carrier bearings, what else do I need?

Also, I have someone who says he can program the change for the speedo but not sure about the trans. What happens if you don't do programming for the trans?

The reluctor may not fit the pinion shaft from the truck. GM may be able to tell you the correct number of "teeth". Check with Hamilton Chevrolet, they are B body friendly. Some 9C1s had 3.42s. If the truck has ABS, it may have the correct reluctor on the pinion shaft.

Installing the pinion at the correct height may be a trial and error issue. You need a pinion height tool for ease of installation. You also need a depth gauge to set your lash.

You need a selection of shims for both the pinion shaft, and carrier. You also need a preload shim installation tool.

If you can get a 3.23 rear from a 91-93 wagon, it will bolt in, and you will be close to your goal with a minimum of effort. You can tune for the gear, it will have the reluctor, and you do not have to mess with the pinion or lash. Some have LSD, but even if you were to replace it with an aftermarket LSD, you would only have to set the lash, and preload.

If you do not tune for the gear ratio, your speedo will be off, and the shift points will be off as well. Your engine may not provide the proper mixture for the given power needed at a given (computer perception) speed.

Thanks for the input. I'll have a shop do the install. 3.23 would be a great option if I can find it.

The SPID code for a 3.23 rear is GU5. The SPID is located on the passenger's side gate jam.