I am trying to replace the rear end on my sons 1999 Chevy Blazer. According to the VIN # it's a 4×2 with a gear ratio of 3.07 (opt GU4) My question is can I replace it with a (opt GU6)? I cannot seem to find a 3.07 at any junkyard. I don't know what to do. Please help!! Thank you

 

Yes you can. The only issue you might have is the speedometermThe might be off. Gear Ratio and Tire Size affect the speedo. If this was a 4X4 the ratio's have to match.
That is the easiest way to accomplish a gear change.

 

There are a few ways to deal with the speedometer being off.

One is to try to guess the difference using some basic math. The best is to have the on board computer, I think the body control module BCM, reprogrammed. Some on-board diagnostics, OBD, readers can do this.

Before I discovered that my OBD reader could do this I used an OBD guage reader to compute my actual speed along with other info such as my transmission temperature. The one I have is the one by Ultra Gauge.

Before you make any change, you'll want to check your actual speed vs. what is on the speedometer with a GPS or a smart phone app.

Of course a smartphone app could be used too I guess!

The only other things to look for is if the axle has a locking differential, RPO G80, and if it has the same setup for the brakes.

The G80 option is nice but not necessary. Some S10 trucks I think had rear drum brakes whereas I think all Blazers had rear disc. I only mention it to be thorough.

 

The G80 is a nice option. I pulled the G80 Diff out of a junkyard axle and installed it in my axle assy. on my 2000 GMC Jimmy 4WD. I swapped my ring gear and set backlash.

 

Thank you guys so much. I've been searching for the 3.07 for weeks now with no luck. So I started doing my own research by pretty much reading these threads and man did I not know anything about Chevy axles. I'm getting ready to go to the junkyard to find a rear end out. Could use some prayers!! Thanks again. Life savers you are.

 

It took me 8 hours but I finally got my sons rear axle assembly completely out. The U-Bolts were a workout to say the least. Even after I broke them loose it didn't get much easier to turn. But it's out and I found a nice used 7-5/8" GU6 option for $250. Now I just have to put everything back together. I'm a little worried about his e brake going back on without a hitch, any hints? I could use any advice really that would make things easier. My son needs his car back. Thanks

 

Take the cover off of the master cylinder and use a clamp to compress the brake caliper pistons back into the bore. You may have to use a paint stick or something simular to compress both pistons at the same time. If your using the calipers on the new axle you will have to bleed the brake lines at the bleeder screws.

 

I appreciate the help. Never done this type of job before so any advice I get is sooooo helpful. Thanks again. Going out to the garage now.