3.55 ring & pinion
That's similiar to what I went through except you got yours looking pretty darn good. Better than mine for sure. Nothing I did would get the pattern in the center of the drive and coast at the same time. I'm gonna pull it back apart next week to see how it looks and see if now that it has lapped in good maybe I might be able to touch it up and get it better. I put about 700 miles on it last summer so hopefully I didn't ruin them. If so I guess I need to start over.
Fishy, my rear is not totally silent either, has a slight whine in decel, nothing terrible but it is definitely not perfectly quiet after putting 100 miles on it I detected some noise in the 48-40 decel(complete lift of throttle). Nothing I can't live with, none of them will be silent in a Duster anyway:)
I did contact the manufacturer again and they said there are two different qualities of gears: Blue and white box(mine and yours) and ones that come in a yellow/red box(premium gears). They only offer their "standard quality" gears for mopar 8-1/4" and most others. National Drivetrain, a heavy supplier of Motive gears even has a standard quality line called platinum and they say those will make some noise but may get quieter as they run in. Hard to believe they would list them like that. I suspect those are made by motive also but can't say for sure.
I suspect our gears finish lapping themselves as they run in. Proabably possible to pull the cover and run a pattern after initial run in and touch them up a little if you don't like the pattern. I bet the backlash opens up on them after run in which can give you some noise too.
Further, motive is a division of Midwestern Truck and Auto parts, there is a separate Motive Performance division which makes most likely the better quality gears. Our gears were made in Korea on top of that. Not knocking them because they are foreign, I had a 2000 Elantra that was the benchmark of reliable and it did not have noisy gears. I suspect the standard Motive gears are more suitable for offroad trucks which is where I have seen allot of their stuff marketed. Hind site is always 20-20....
I looked at your post from last year and saw what you went through on set up, about the same as mine. Some gear sets are going to have some noise and I think these are one of them. Neither one of our sets would allow drive and coast to set up at optimum, one had to sacrifice for the other. Mine are still not much worse than my stock gears in my 06 GTO. I noticed taking my goat out of overdrive makes the gears noiser on decel too because the engine puts more load on the coast side of the gears in the lower drive ranges. My Duster of coarse has a 904 in it with no overdrive. I think a liberal dose of Dyna-mat is in order!
National drivetrain lists the different catergories of Motive gears, I suspect their Platinum Torque line is made by Motive also. Here is the link, good read:
http://www.nationaldrivetrain.com/ring_pinion_info/basic_overview.html
