New gears hum

[Oldsschool79]

Hello everyone, hope everyone enjoyed the holidays!
Looking for some input on rear gears. When I restored my '79, I installed 3.42 Richmond gears. I had a 2series carrier and used the spacer behind the ring gear to avoid replacing the carrier. Everything went well on setup. I have a hum on decel that goes away with accel.  Now that the winter months have hit, I tore the diff. down, the pattern looks perfect, back lash just at .010. I took a reading on the pinion depth and it is dead on to the spec. engraved on the pinion at 2.251. Based on everything I see there is nothing not set properly. I have read many articles they are niosy.
Has anyone used the gears and had the same result?   Thanks again

[wheels78ta]

Do you have any pics of the pattern?

What are the backlash tolerances?

[b_hill_86]

When I had a rear rebuilt the builder had a disclaimer that he does his best to avoid any noise but in a nutshell it happens sometimes. I have a tiny bit in mine but livable.

[nUcLeArEnVoY]

Mine hums like a Blues singer on decel, too. I've just grown used to it.

[Oldsschool79]

The backlash was .010

Thank you all for the replies

[rkellerjr]

Mine had a hum and I put some ... elephant something or other in it and it stopped. maybe someone else knows what I'm talking about, this was many years ago.

[Oldsschool79]

I do remember the gear oil being called elephant or animal , well you know. It was used in heavy truck applications.
Looked like one step away from grease.

[tinpusher]

Did you check the condition of the spider gears in the posi unit…. I just went through all of this after getting a pro to set up the rear end , the posi had a great deal of slop and wear. We ended up replacing it with a Yukon posi and it’s nice and quiet. I was just going to replace the spider gears, but got a great deal on a new Yukon differential on Amazon. It was only $288 delivered. I was going to buy a second one , but the next day the jumped in price.

 
Yukon Gear & Axle (YDGGM8.5-3-28-1) Duragrip Differential for GM 8.5 with 28 Spline Axle
Sold by: Amazon.com Services, Inc
Return eligible through Feb 4, 2024

[nas t eh]

I just had new AAM 3.42 and Eaton Truetrack installed in my 8.5 rear.
The shop said the better quality gears are less prone to noise but that all gears need to be babied for the first bunch of trips or up to 1000miles.

Short trips, lower speeds, no hard acceleration or the heat will build up and cause noise.I am almost though the break in period on mine and at that point, they want it back in the shop for gear oil change

[wheels78ta]

The backlash was .010

But what is the tolerance for the backlash.  .010 seems high.  Shouldn't it be in the .030-.080 range?

And noise on deceleration is usually the pinion being too deep.

Did you have any load on the axle when checking the pattern?

Seems like it could be a couple of small things to adjust to get the humming gone.

In the past.....Richmond gears were known to be noisy but they have improved over the years from what I've read.

I've re-geared axles before and never any noise.

[olds403]

Richmond gears will hum.  Did a set in 1986 or 87 I forget with the 3:23 and rear spacer.  It was done by shop back then. 
That rear is now in our 10th Anniversary Trans am.  The best gears are GM and when did my other rear end I used a set from C15000 truck.   
I would just move on.  It is the way it is. 

[wheels78ta]

I will not say that the noise is good in any sense but I've never used Richmond gears.

On the plus side.....it's better to have the noise on the coast side than the drive side.....And depending on how loud/rough the noise is.

Just because Richmond gears are known for being noisy doesn't mean there isn't a problem.

The .010 backlash puzzles me.  That just seems too much.

Since is doesn't sound too severe I would drive it.  If the noise gets worse/louder.......pull the cover and check the oil.  Also check the pattern while you're in there.  If pattern looks good and nothing found in the oil....let it ride.

Sometimes a different viscosity of oil will take care of the noise along with putting some miles on it.

[Oldsschool79]

So I reset the backlash to .004 , the tracking looks perfect. I ran it through the gears on jack stands loading the diff with some braking. Hard to tell if I changed anything. Would love to get i ton the road but there is a ton of sand and road salt here. I will post the results from the change when it hits the road. Thanks again for all the help!

[Oldsschool79]

Finally good weather and cleaner roads! I got it out yesterday and it looks like I only have a slight hum on accel after 45 MPH. It is loud but I think its just the brand. Everything in spec., no metal and a perfect pattern.
Thanks for all the responses.

[wheels78ta]

Glad the hum is a bit quieter.  Now it's time to enjoy the ride.  Spring is almost here.