Is there an RPO code or an other indicator that will let me know if I have 28 or 30 spline axles? I have a 99 silverado that cam with a 5.3, G80, and 3.73...
Any one know?

 

You should be able to call your local dealer and give them your vin and get that info for you.

 

30 spline....

 

Thanks I didn't know if it might be a 28 spline being the first year. 99 models seem to be an odd year where parts are concerned.

 

No guarantees, but my friends ’99 SBSC had 30 spline axles in his.

 

30 spline 8.6 rear. only s-10 and f-body 7.5's had 28 spline I think. but I am sure yours is 30!

 

+1

All 8.6" have 30 spline.

Some of the 8.5" axles had 28 Spline.

 

I called Jaws to order a trutrac and they told me it could be either and i had to tear it apart to tell. Not really into that!

 

That's because the TruTrac is made to fit 8.5" rear ends...the 8.6" happens to be the exact same rear end except its .1" larger.

I have never seen a 28 spline 8.6" rear. And if I am not mistaking the G80 is not made in 28 Spline.

913A481 is the P/N you want.

That's for 88-09 trucks with 30 spline 8.5" and 8.6" diffs
The last 8.5" made with 28 spline was 1989.

 

its an 8.5/8.6 30 spline without doubt.