In my 1992 RS, we put in an IROC rearend with 26 sline axles. The gears are whining on acceleration cause they are worn. I still have my old '92 stock drum rearend, as well as a 1995 Z28 rear end. I need to know if I can use the 28 spline axles from the '92 along with the 4th gen posi unit, and drop it all into this IROC rearend when I replace the ring and pinion? Weird combo, but the posi is free, and I'm sure the old one is worn out so if it will work, let me know.

 

Yes 28 spline 3rd gen axles + 28 spline 4th gen posi + 3 series gears = good rear end. You might try checking out your rear end first. I worked on one around a year ago that was just as you said. The gears were noisy, I thought it was wear on the gears. When I inspected the gears they were fine. Instead the washers outside of the carrier's races were destroyed. This allowed a ton of backlash. I replaced the washers and rechecked the backlash and found it was good. The rear end went back silent after 300-500 miles. As far as I know it is still silent and working.

 

would that be better and still keep the 26ers? I don't want anymore costs and work than I have too, but it needs to support over 300hp. I hated going to 26 spline, but the posi and rear disc were well worth it for the 300 dollars(that was installed for me too). Thanks for the input, anyone else??

 

Would it be better to use 28 spline axles than 26 spline axles, that is an easy one. Yes. I made the suggestion because $5 of parts and 20 minutes of work to fix a rear end is about as easy as it can get. I didn't want to you overlook this possibility I have seen. I haven't seen a 7.5" axle desplined, be it 26 or 28 spline axles. The gears or cross shaft always bust first. Now I am certain someone is going to turn on their flame thrower with some picture of a desplined axle. Sure it can and probably has happened but they are not the weakest link. Keep in mind the 8.5" ten bolt uses 28 spline axles and still those tend to throw gears or posis more often than axle splines. So don't feel too put out that you have 26 spline axles. They should hold up to 300HP just fine. Now if you have to rebuild the axle then I would be all for using the old 28 spline axles and a 4th gen posi. Just make sure you can't easily repair the old one before feeling pressured to build a new one.