I have a 99 Blazer 4x4 and i just lifted it 2 inchs and put 31x10.5 mud tires on it. I have herd that puting lower gears helps the engine push tires easier making it faster off the line and supposedly get better gas milage. Does the lower gears really help and if they do what size should i use i was thinkin 4.10 gears with a locking diff. And were would i get the gears and locking diff?

 

Check out this thread: Gearing

 

If after reading that thread you still want to change the gears, Synergy Offroad has some good stuff. It's run by a member here Jigg, and it's pretty awesome..check it out. Lockers and Gears

 

thanks the tread helped but are the codes there talkin about on the door? and ive herd that the only blazers with the 3.73 gears are the zr2's. And r our axles 10 bolt 8.5 inch rearends? And how do u figure out if you have a 30 spline or not.

 

The codes mentioned in the thread are the RPO codes found in your glovebox. It's a white label with lots of 3 digit codes on it, and each code correlates with a feature/option on your truck.

As for the splines/diff sizes, that still boggles me, i'll let someone else handle that

 

The axles used in the vast majority of the S-series trucks are 10bolt 7.625" ring gear axles. 3.73:1 gears were available in any vehicle. My Bravada had 3.73 gears.

As far as the spline count, I believe that the 7.625" axle has a 28 spline axle shaft, but do not quote me on that.

 

From like 1992 onwards, or whenever GM switched the S-Series to the 7.625" from the 7.5", they're 28 spline... The 7.5" was 26 spline.


If I remember right, the 8.5" is 30 spline.


Unless it was a special order, you do NOT have the 8.5" rear. That was only in ZR2's or 5-speed rigs.