I was pleased that my new 4.11 Moser 12 bolt was stil quiet after a gentle 300 miles, done 25 miles at a time with cooling time in between. Then I made a pass at the strip today and it started howling on decel. I understand that if the pinion depth is wrong, any rear end can howl and the solution is to get it set right. But why would the noise start after one pass (this is a stone stock 2000 Z28 with Moser and BMR pieces)?

 

The 300 easy miles didn't break it in.The 1/4 mile passes will seat the gears in.It's very common to get louder after a few passes if the rear is not set up right.

 

should have went with a strange!

 

What does "seat the gears in" mean? A race wasn't seated and sidestepping the clutch seats it?

It wasn't a few passes, it was one pass. By not set up right, do you mean pinion depth wrong? In which direction?

I took the 12 bolt apart today. I have 4.10 Motive gears in it. I measured the backlash at .009, which is on the tight end of the spec (.008 - .012). The contact patch is larger than I have ever seen with OEM gears, and is biased a bit toward the heel, but not obviously way off. I can't check pinion depth as I don't have the tool, but I did verify that there is no endplay in the pinion. Long story short, I still don't know what prompted the sudden onset of howling on decel, but since everything looks OK, I will ignore it.

 

Heavy contact on the Heal will ussually mean the pinion depth is too deep.That WILL make the rear whistle.Just taking .004 out of pinion depth makes a world of difference.

 

I had the same problem with the Motives, they seem to be really intolerant of pinion depth imperfections. I chewed up 5 sets in 2 months.

I switched to Richmonds, and now after 2 years, quiet as a mute.....

I would shallow up the pinion depth as earlier stated....

 

Thanks. Where do you get shims? Do you need a spreader to pull the posi (like we had to for the Danas)?