gear pattern changed.

[RealLiveMD]

As some of you have been following, I switched to a 3.90 gear which was quiet and the pattern changed after a WOT run. Tried another, it whined on the coast side, switched to 4:10 and the pattern changed again just like the first 3.90. When the guy install the gear, he illustrates good contact. After driving the car around the block the pattern is clearly on catching the lip of the ring teeth. What is he doing wrong? We're trying another 4:10 tomorrow but this one is going to be a GM original instead of Motive high performance.

[BlwnCamaro]

As some of you have been following, I switched to a 3.90 gear which was quiet and the pattern changed after a WOT run. Tried another, it whined on the coast side, switched to 4:10 and the pattern changed again just like the first 3.90. When the guy install the gear, he illustrates good contact. After driving the car around the block the pattern is clearly on catching the lip of the ring teeth. What is he doing wrong? We're trying another 4:10 tomorrow but this one is going to be a GM original instead of Motive high performance.

The only way it could change is if the bearings are not preloaded enough or have lost there preload which can happen in a crush collar type rear end if you dont torque down enough or if later down the road you really hammer rear end it can unload. I've seen them unload during breakin also but usually doesnt happen if torqued properly. 26 inch pounds of rotational resistance on pinion bearing usually takes over 250-300 pound feet of torque on pinion nut to achieve depending on the size and model of rear end you have. I use a very strong impact and then check rolling resistance in steps. Some like the solid shim setup but I have mixed feelings about the setup procedure on those but they are supposed to hold preload better in theory.
Also if the carrier isn't shimmed and preloaded properly on its bearings it can fluctuate also.

If it is only catching on edge of tooth than the pinion depth is too deep and the pinion needs to be shimmed closer to the ring gear and the proper backlash set with the correct preload. Which rear end do you have? Rears can be tricky to set up properly. The use of a dial indicator with a jig can allow you to measure pinion depth and backlash cause every set of gears is unique and comes with a recommend pinion depth from centerline and recommended backlash setting. I can set them up without dial indicator but it usually means pulling and shimming a few times until I see a good pattern. Once you actually run the gearset in a certain pattern if it is wrong the gears are virtually ruined as you have experienced. Hope that helps, I build many fbody rear ends for my customers and my various cars.

I'm not sure what techniques your guy is using but I can tell you it takes a very close eye to detail and the right experience and tools to successfully install gears, bearings and shim properly. Even having said that some aftermarket gear sets still have a tendency to whine a little even with an ideal pattern and preloading. I have put much time, hands on, research and experience into the dynamics of properly building rear ends and it is more complex than some would think. Many shops and dealerships dont know what they are doing not to be rude, but its true you would be amazed.

[BlwnCamaro]

furthermore dont mean any disrespect to your mechanic there are actually many variables and deltas in the realm of gears. It is not uncommon to see a failed aftermarket gearset that didnt or wont take. If you delve into the world of gears and rears it does happen.
Some further anomolies that go beyond human error in terms of correct shimming, torqueing and preloading, include rear end housings that are tweaked and out of spec, defective noisy aftermarket gearsets, defective bearings, bad bearing races. So as you can see there are many variables.

Did he also replace all of the pressed in races in the rear end. Sometimes people dont replace pinion races cause it can be a pain but that can be devastating.

[RealLiveMD]

furthermore dont mean any disrespect to your mechanic there are actually many variables and deltas in the realm of gears. It is not uncommon to see a failed aftermarket gearset that didnt or wont take. If you delve into the world of gears and rears it does happen.
Some further anomolies that go beyond human error in terms of correct shimming, torqueing and preloading, include rear end housings that are tweaked and out of spec, defective noisy aftermarket gearsets, defective bearings, bad bearing races. So as you can see there are many variables.

Did he also replace all of the pressed in races in the rear end. Sometimes people dont replace pinion races cause it can be a pain but that can be devastating.

I'll have to check about the pressed in races. I don't know, the guy seems to not want to give up. He says that he's done plenty gear swaps. they were doing a swap on a 12 bolt in a 1100hp SS while I was there last night. He says he's never seen anything like this. Especially, with the first gear being quiet until I punched it after the 500 mile mark. I'm just tired of my car being in the air over and over again. I still have a stock 10 bolt with 386rwtq. . I'm $650 in the hole now. I'll be $1000 in the hole if he can get it right or walk away, and stay $650 short.

[RealLiveMD]

update, he couldn't get the gears right so he put the old one's in and gave my money back. Surprisingly the old ones are fine when the 3 diff aftermarket gears whined and howled. Go figure.