So, I just replaced my upper and lower BJ's/CV Axles/Sway bar ends on both sides over the weekend on my 99 4x4x4 Blazer. In the process I noticed the gasket on the driver side of the front differential has gone bad and leaked what I'm assuming is all the fluid out. Currently I have the 3:42 gears in but I would like to swap the rear out for a ZR2 and swap the front to the matching 3:73 ratio. I just want to make sure of this next part so I don't screw myself in the long run. I can put the front differential in with the 3:73 gears and not do the back as of yet as long as I DO NOT use 4wd, correct?

And also, are the front CV splines the same number for the 3:73 as the 3:42? Bc i just put the brand new ones in and would hate to have been out the $200 for them. I know the rear end axles are a 30 spline opposed to a 28 spline and I'm pretty sure the front doesn't change but I'd just like to make sure.

Thanks in advance

 

Correct, if you do not use 4wd, you will not damage anything. For added insurance, I would disconnect the vacuum line at the front axle actuator and plug it with a golf tee (or other suitable plug). This will ensure that the front axle does not engage under any circumstances.

As far as the spline counts, nothing changed there.

 

That's what I was hoping to hear. I can get a used differential with under 80K with the 3:73's for $150. I'm up in the air about whether to do it myself or just have them put it in (another $200). Just gotta find a decent ZR2 rear end (hopefully with a working posi) and get that home and all cleaned up and i'll be set.