Eaton Posi Differential 30 Spline 1.32in Axle Shaft Diameter 2.73 & Up Ratio Fr/Rr 8.5in /...

The Eaton Posi 19559-010 is a clutch-type limited-slip carrier for the GM 10-bolt 8.5 in. and 8.6 in. axle with 30-spline, 1.32 in. axle shafts and a 2.73 or numerically higher ring and pinion. That covers a huge number of 1988-and-later Chevrolet and GMC half-ton pickups, Tahoes, Suburbans and vans, plus 8.6 in. cars. People shop for it when the truck leaves one black stripe pulling away from a light, when the stock G80 locker has broken or worn out, or when an open carrier spins a tire on a wet boat ramp.

What the Eaton Posi does in a GM 8.5 or 8.6 10-bolt

Behind each side gear sits a clutch pack made of carbon friction discs and steel plates, and a central spring assembly keeps those packs preloaded all the time. Under steady cruising the clutches slip just enough to let the wheels turn at different speeds through a corner. When one tire loses grip, the preload and the separating force of the gears resist that slip and push torque to the tire that still has traction. It works on its own with no switch or air line. Because the spring packs can be changed, the engagement can be tuned firmer or softer, and the unit can be rebuilt with new clutches later instead of being replaced.

Symptoms that point to this carrier

• One rear tire spins on launch, gravel or wet grass while the other does nothing.
• A factory G80 locker that no longer locks, or one that has broken its governor or flyweight parts.
• An older posi that has gone loose and now acts like an open carrier.
• Rear-end whine, bearing noise or worn spider gears found while the cover is off for a 10-bolt rebuild.

How to confirm it fits before you order

With the truck in neutral, lift one rear tire and spin it. If the other side turns the opposite way, the carrier is open or worn out. Next confirm three things: the 10-bolt cover with an 8.5 or 8.6 in. ring gear, 30-spline axles, and a 2.73-or-higher ratio, since Eaton breaks GM carriers by ratio. Our GM 8.5 10-bolt problems and rebuild cost guide shows how to identify the axle, and carrier break explained covers why the ratio matters. Still deciding? Read open vs limited slip vs locker.

Fitment

Eaton's application guide lists 19559-010 for GM 10-bolt C-clip 8.5 in. and 8.6 in. axles with 1.32 in., 30-spline shafts and 2.73 and up gearing, across GM cars and 1500 trucks, SUVs and vans from 1988 forward, plus the 2006-09 Hummer H3. The listing title also names front 8.5 applications, so a front-axle buyer should match spline count and shaft diameter first. Early 28-spline 8.5 axles and 26-spline 7.5 axles need a different unit. Send us your year and VIN or the axle tag if you want a second check. More axle parts are in our hard parts category.

Install notes

• Eaton states all of its GM 8.5/8.6 carriers need specific carrier bearings. Small-bore housings (2.89 in. race OD, mostly before 1999) take LM102949 bearings with LM102911 races; large-bore housings (3.06 in. race OD, 1999 on) take LM603049 with LM603012. Measure your races before ordering.
• A GM 8.5 carrier install kit with HD bearings or the standard 8.5 carrier install kit covers bearings, shims and hardware.
• Transfer the ring gear with new bolts, set backlash and preload, and check the pattern. If the gears are worn, pair it with a new GM 10-bolt ring and pinion set.
• Fill with a quality GL-5 gear oil, mineral or synthetic, with enough friction modifier for a clutch-type limited slip; see our friction modifier guide.
• Do a gentle break-in with some figure-eight turns before towing or hard launches.

Will 19559-010 fit my 3.42 or 3.73 geared truck?

Yes. It covers 2.73 and numerically higher ratios, which includes 3.08, 3.23, 3.42, 3.73, 4.10 and up on the GM 8.5/8.6.

Does it fit a 28-spline 8.5?

No. It is for 30-spline, 1.32 in. axle shafts. Eaton lists older 28-spline 8.5 axles under Posi 19557-010.

Which carrier bearings do I need?

Eaton calls for LM102949/LM102911 on small-bore housings, mostly before 1999, and LM603049/LM603012 on large-bore housings from 1999 on. Measure the bearing race OD to be sure.

What gear oil should I use?

A quality GL-5 mineral or synthetic gear oil with enough friction modifier for a clutch-type limited slip. Add more modifier if it chatters in tight turns.

Can this replace a factory G80 locker?

Yes, it drops into the same 10-bolt 8.5/8.6 housing in place of the G80 or an open carrier, as long as the spline count and ratio match.

Can it be rebuilt later?

Yes. The Eaton Posi is rebuildable with new clutch packs, and the spring packs can be changed to tune how firmly it engages.