epfatboy

iTrader: (3)

What are my chances that when installing my new posi (Eaton) in my 12 bolt truck rear that I won't need to mess with pinion shims?

Re-using my GM gears and expect to shim the carrier

FirstYrLS1Z

iTrader: (4)

If the pinion depth was OK and bearings OK,replacing the carrier/posi will only effect 'lash'.
You stated you're re-using your GM gears,you should be only removing the ring gear or are you removing the pinion too ?

epfatboy

iTrader: (3)

Planned on leaving the pinion alone if I can.

I'll check pattern and backlash before I pull the ring.

Got the rear out of the truck tonight, just waiting on posi and disc conversion

FirstYrLS1Z

iTrader: (4)

As carriers/posi units are made to a spec for the rear they're to be used in,sometimes the lash won't change when using the new one when leaving the pinion untouched.

biketopia

iTrader: (5)

Yup, I'd pull the carrier and swap your ring gear over. Keep all spacers and shims in order and on the correct side. I bet you'll be damn close, if not good to go once you get it back together and check your pattern.

epfatboy

iTrader: (3)

Well orig shims were same size each side and backlash measured .012 before disassembly.

Could not get the Eaton posi and new koyo bearings back in with the orig shims. Took .020 out of each side and back lash is now .010.

Need to get marking compound to finalize pattern. Tried to melt in some tire crayon, looks like I'm more to the toe than I'd like but read used/orig gears are normally more toward the toe. I'll throw some pics up once I get some readable patterns.

Note I tried to use orig shim on ring side and pulled .030 on opposite but pinion was binding so I decided to pull .020 from both sides.

Is .010 in tolerance for a GM 12 bolt?

FirstYrLS1Z

iTrader: (4)

.010 is on the loose side. I, typically, do .006 for manuals and up to .008 for auto. Make sure you check backlash in four places of the ring gear to make sure the ring gear/carrier is running true. Don't apply too much marking compound as the smearing of the 'excess' will mask/hide the true pattern. The 'carryover' of the marking compound to the unmarked teeth will also show the true pattern.

FirstYrLS1Z

iTrader: (4)

here's a past thread concerning too much marking compound.

https://ls1tech.com/forums/gears-axl...ern-check.html

epfatboy

iTrader: (3)

Thanks, gotta wait till the marking compound gets here, could not find any locally, not even at the dealership.

epfatboy

iTrader: (3)

More info.

I tightened the backlash to .008 by adding a .005 shim to the ring side shim pack.

The pattern is listed as acceptable on some sites for used gears. My question is what causes a heavy drive toe pattern and a heavy heel coast pattern?

https://photos.app.goo.gl/PGNeRRmielHsj8532

https://photos.app.goo.gl/V6vZNuu7hddsXFt97

FirstYrLS1Z

iTrader: (4)

Have you checked pattern in more than one area ? that kind of pattern with .008"(at that area) should be better than that.

epfatboy

iTrader: (3)

I have used 3 spots, same pattern in each of the 3. Backlash was .008 in 2 of the spots and .007 in the other but that could just have been a small difference in my setup so I ignored it.

I could flip the shim packs and move the .220 to the ring side and .230 to the other side to see what happens but I think that would just increase backlash and likely push me out of tolerance and I honestly don't know if it would move me off the toe/heel.