I have a 3.08 rearend and I want to put in a posi with at least 3.42 gears. I have heard I have to change out the whole rear end. I was wondering if that's true or could I just change the gears thenselves and install a posi?

 

You can change out the gears and posi but it's just alot cheaper and easier to do the whole rear end. To have the gears swapped your going to want a great mechanic who knows his rear ends to line up the pinion and gears. A rear end you can find for anywhere from $100-$300.

 

3.08 in a '98 -- really? did you verify your RPO gear code, or was this rear already replaced?

 

Yea it an auto. The code is GU4 I just rechecked. It hasn't been replaced it's all stock

 

I thought 3.23 was the lowest they went on 98+ -- I would just have the gears and carrier replaced on yours and check the bearings while you're at it... You could get another rear only to find out that it needs new bearings -- then you still have to open it up.

 

Ya just change the carreir and gears. You have a hard rear end to find a replacement for. The 98+ rears are different then the 93-97 rears.

 

3.23 was stock on models with the 5 speed

 

So what you need to do is find a rear end from a z28 any year from a 93-02. Steal that carreir and buy some new gears in the ratio you want. A carreir new your looking at around $500. Gears are around $200. Labour to Install the gears $300 plus the instalation kit is around $100.
You can install the gears yourself but you better be a very pateint guy as it can take a long time to get the pinion gear perfecty centered. If they aren't you can do some serious damage to the diff internals or have a really noisy diff.