12 bolt clunk/binding
 

My rear end was just rebuilt. New US Gear ring and pinion, new right side axle, seals bearings, etc. They said the differential/carrier was good. No leaks. It's smooth and quiet, except when it's hot. At low speed, when turning (mostly left turns) I get a couple little clunks and it feels like it binds for a second, then it's fine. We went through the manufacturer's break in procedure (which isn't much) and I've been pretty easy on it. It's got probably 100+ miles on it. I don't know what oil or additive it has in it. So I've read that this can be wrong or no additive or normal or a bad differential./clutches. :Probably start by adding some GM posi additive??

I would add some additive to it and just drive it.

+1 on the additive....then a few figure 8's ....(without smoking the tires...) Some gear oils state "no additive needed" ....well i havent used one yet that you didn't get the "clutch bite" KICK....

Sounds good. Thanks!

Good idea on the figure 8's

Detroit Lockers always squeaked around corners, was one sign of a hot car.

The gear oil installer did not add a bottle of additive I would 100% .. Go get a K&W TransX Posi-Trac limited slip gear oil additive at Autozone

I thought it was usual practice to change the gear oil after breaking in a new set of gears. I have used different brands of oil that claimed to have the additive in it, only once did I have a problem with chatter and I added a half bottle of the GM stuff to it to bring it around. I do not know if I would go in blind with more additive than what is needed. I'd suggest new gear oil with your choice of additive already mixed in or the regular stuff and add some.

US Gear does not mention oil change after break-in but other manufacturers and other sources say to change it after 500 miles. I guess the safest thing to do is to change it now with additive and then do it again at 500 miles. Also, can this noise be normal for a new gear during break-in? I had it out for a short drive a couple days ago and it was quiet. I'm taking it out today for a slightly longer run so we'll see what happens.

So is it the gears slapping around due to clearances or is it posi clutch chatter? Big difference

I don't know for sure since I'm not an expert, but as time goes on it seems more like clutch chatter. No straight line noise. No noise at speed or under any load condition. No noise going from forward to reverse or vice versa. It only does it at very low speed when turning, mostly turning to the left it seems.

I had it out for a drive today and got it good and warmed up. At the end of the ride there was just a hint of chatter turning left at very low speed. It was barely noticeable today. In fact, if I wasn't previously aware of it, I probably wouldn't have noticed it today. So it seems like it's getting a lot better.

I wasn't able to find a good place to do figure 8's today but I'll do that soon. I also have some GM posi additive on the way.

Whenever I rebuild these rears, I soak the clutches in the additive. Never had one chatter when you do this.

After the figure 8 turns and a little more driving It's basically gone. Thanks for all the advice.

Nice

Just curious, but did your builder show you proof of the contact pattern and backlash?

A good shop would usually mark it on the ring or give a printout showing it's within spec


https://i.postimg.cc/W4yKMRT4/IMAG0708.jpg
https://i.postimg.cc/d0pLy0fS/IMAG0714.jpg
https://i.postimg.cc/g0QygNf4/rebuilt-RRrear6.jpg
https://i.postimg.cc/SK5mvMQm/rebuilt-RRrear2.jpg
https://i.postimg.cc/9fSJwWbx/rebuilt-RRrear3.jpg

Setting up gears right is a bit of a lost art that I wouldn't just trust anyone to do.

You'd be surprised how many fresh built replacement rear ends come into my shop with gear setups that are way off

Nope, I didn't get that information from the builder. But like I said, It's quiet and smooth right now. Maybe that's just because all the teeth are ground off the gears. :eek:

Hope it is all good. Sounds promising. I am not a gear expert. Had a traction lock added to my open gearset last year, luckily it went well, guy was good. I didn't want to post on this, but my life experience with clunking rears has not been good. But in my past life I would test them to the limit and then some.