Question for Differential Experts
 

I have a 12 bolt posi I bought from a small shop. The housing is OEM but the posi unit is a new Yukon it's got new 3.08 gears, new bearings, new steel axles etc. The rear end whines constantly under light load and stops when you back off or let off the accelerator. The guy that I bought it from said it's the gears and there is nothing that can be done. I don't buy his response, but I can't make him fix it. I want to know what I need to do the get this rear end quiet like it's supposed to be. Thanks

I have the same issue with my 12 bolt, 3.07. I've lived with it for a few years now.

Curious to hear what the experts have to say. Subscribed.

:confused:

I'm no expert just a backyard guy. I was told by a professional my stock 8.5 that I raced set backlash at 0. It will increase after first couple of launches. Yours is different I know. I've done used gears and tried the lower side of recommended backlash. I haven't had whine. Maybe I'm lucky. Ck your back lash first. Then clean gear teeth apply say grease and ck pattern. That will tell you pattern

Typically once they whine and take a set, there is no getting rid of it at that point. Most likely it wasn't set up correctly from the start, either pinion depth, back lash, or both, and they'll tend to make noise. Since yours whines under load and is quiet on coast that's usually typical of the pinion depth too shallow and needs more shim. If it would howl on coast that's usually excessive back lash.

Unfortunately. You need to start over with new gears. Those have joined like a flat tappet cam and lifters. Bummer.

Nobody sets the backlash at 0...I'm sure he meant its set up tight at the low end of tolerances..like .006

This -

and this.

K

I think it depends on just how "new" the gears are as to whether they have taken a set yet. Certainly wouldn't hurt to check the setup and see if something is whacky before you replace the gears.
I just replaced all the bearings in my diff that was whining badly (100+k miles). My whine was caused by sloppy clearances from worn bearings. Replaced the bearings, checked the setup ... absolutely quiet now. So I'm not sold on the idea that once they whine there is no curing them ... but then my gears were well worn, and had taken a good set long ago when the bearings were good.

Have you checked the backlash? I'd have to try and shim it a couples of thousandths either way and see what happens. We used to swap gears around before we had any clue and no indicators. Played with shims until it sounded good.

Since you say it’s all new ( how do you really know about the gears though? ) I would pull it all down and polish over the leading and following edges of all the teeth on both gears and then set it up again.

If not at least with the way it’s whining only during light load and deceleration you should not see much ware to be concerned about, just depends if you can live with the noise?

Basic task in theory, yet tough labor in practice, to re-shim the pinion. So INSPECT backlash for loose vs tight. And try to get a tooth mesh pattern while in there.

Tooth pattern: look for "hi-lo" contact for Forward and Reverse. Also depth of engagement.

If engagement depth is too shallow then pinion need shimmed out. Too deep (rare), then remove some shim.

Goal is tooth contact in tooth mesh middle zone (as equal as practical) for forward and reverse. I think


When all quiet, use Redline AntiShock gear "oil". For zero wear. Posi additive is a must with that stuff.

^^^This^^^

First off. The gear vendors say dont hammer your gears until you have broken them in. Hot and cold a couple times and 250-500 miles. To me that means they have taken a set. Howling/whining/what ever, gears after that point a fuuked to me. Maybe you get lucky and shut them up. Maybe you and your buddies dick with it for a couple weekends on and off for a few months. Thinking you got it quieter. Replace the gears, pay a pro and enjoy your weekend, cheapo.
This doesnt apply to the OP. Just venting. Rear ends and headliners are a trigger for me!

Boy, that escalated quickly, HAHAHAHAH.

I must say that I can't see the ring and piñon gears due to there thickness and metallurgy taking on a set by being run however many miles you care to talk about
However waring in a bit is a different story.

Maybe the whole rear assembly minus the gears had been beat on so much or involved in a accident such that it is out of wack.

Surly the temperatures that a rear runs at with the needed level of fluid in it will never run hot enough to change the tempering of the gear package.

Just like with engine bearings sitting in there respective journals will be thrown off by the smallest spec of crap under them, so will a Bearing cup be cocked if there's a spec of crap that does not allow it to seat perpendicular.

The OP should pull it apart, or have someone pull it apart and inspect all of it in great detail.

Crocie is correct and the same thing I mentioned, once they make noise, they are pretty much set in their way and no amount of adjustment changes that.

Gear setup is critical to get absolutely right the first time.

Most of them I've been involved with is a pinion depth issue because many don't have the proper pinion depth tool to set them correctly so they wing it and call it good if the pattern looks ok. Problem is the naked eye won't detect .010" or .020" off and that's enough to cause an issue. Your gear whine on coast is a classic pinion depth too shallow issue and I'd bet money whom ever set it up didnt have a pinion depth gauge.

There is a reason why new gear sets have the pinion depth scribed right on the face of the pinion. In Most cases the gears are already lapped in at those measurements and anything that deviates from that is setting up for a noisy gear set.

^^^ Wisdom.

I'm not that thrilled with setting backlash on "most" differential cases. Screw-type adjusters on both sides make it easy. Screw-type adjuster on one side makes it kinda easy, but you still have to source a shim in the correct thickness. Shims on both sides, like most integral axle housings? Ick. Now you need a case-spreader, or a hammer and lotsa luck.

It has less than 50 miles on it since installed. I will take it to a professional and have him check it out and if necessary, have him put new gears in it. I don't have the correct tools and know nothing about how to set up a differential. Not sure this is something to YouTube, even so I don't have the tools. Thanks for the responses.

After watching this YouTube video I may do this job myself. First I will correct the pinion depth and shim the carrier to spec. If it still makes noise, I will buy a new set of gears and install them. This is a great video on how to set up a 12 bolt rear end.

https://www.youtube.com/watch?v=DRWhDRIaR6w

There is a bit of misinformation in there on the pinion seal.

The correct pinion seal for a passenger car 12 bolt is still currently available under the Ratech line. Part number 6109

Using the correct seal eliminates the need to do all the monkey business with welding rod trying to space that seal out.


You shouldn't need to worry about that Tim since you're just doing an R&R of the gear set to re-shim some things, but for others that may watch the video, just get the correct seal.

The problem started when most auto stores considered the passenger car 12 bolt seal obsolete and only carried the truck 12 bolt pinion seal as the 12 bolt truck rearend stayed in production much longer, and has a slightly longer pinion snout, hence the depth change in the pinion seal. What's worse is that auto stores will tell you they are the same for 12 bolt passenger car and truck because that's what their computer says. That is absolutely incorrect. Even ring and pinion setup kits comes with the wrong seal, which blow me away. I let the auto stores slide but you'd think at least the gear manufactures would know the difference.

You need the shallower seal, Ratech 6109, for a passenger car 12 bolt. Most auto stores may not carry the brand but they are still out there available if you look around. I usually buy them a few at a time from Summit Racing.