Limited-Slip Chatter and a Load-Sensitive Howl

They are two separate faults that happened to appear after the same service, and conflating them is the trap here.

The chatter is almost certainly the fluid. A limited-slip differential relies on friction modifiers in the lubricant to let the clutch plates slip smoothly. Plain GL-5 oil without the modifier makes the plates grab and release, producing a shudder on tight turns. Fix: drain, refill with the specified fluid plus the correct dose of friction modifier (or the OEM limited-slip fluid), then drive a series of slow figure-eights to work the fluid into the clutch packs, and recheck. If chatter persists, the clutch packs or preload shims are worn and the carrier needs to come apart.

The howl is mechanical and will not be fixed by fluid. Correcting the fluid is still the right first step - it is cheap, it addresses a real defect, and it removes one variable. But tell the customer up front that if the howl remains after the fluid change, the axle has to come apart. Do not let the fluid change be sold as a cure for the noise.

Work from least to most invasive:

1. Confirm where it comes from. Road test with a passenger listening, or run the truck on a chassis dyno/stands. A stethoscope on the pinion nose versus the carrier housing separates pinion bearing noise from carrier/ring-gear noise.
2. Character of the noise. Ring-and-pinion gear noise is speed-related and strongly load-dependent - it changes between drive and coast because the contact shifts from the drive flank to the coast flank. Pinion bearing noise tends to be more constant and often grows with speed regardless of load. Carrier bearing noise can change when cornering as the carrier is loaded side to side.
3. Static checks. With the rear wheels off the ground and the driveshaft disconnected, feel pinion flange endplay and rotational drag, and check for roughness. Check pinion seal seepage, which often accompanies a worn pinion bearing.
4. Inside the housing. Measure backlash and ring gear runout against spec, check carrier bearing preload, and run a marking-compound pattern. A pattern riding off the heel or toe, or concentrated at the tooth ends, explains the noise even with acceptable backlash.
5. Fluid inspection. Drain through a filter and check the magnet. Since the noise began after a service, also verify that the correct quantity was installed - an underfilled axle whines - and that the correct fluid went in.

Ring and pinion gears are lapped together at manufacture and must stay in matched pairs. You can reuse the pair only if all of the following are true:

• The contact pattern is centered on the tooth with no concentration at the toe or heel.
• No scoring, pitting, spalling, or rippled tooth faces.
• No cracked or chipped teeth and no damage to the ring gear bolt holes.
• The noise is attributable to bearings or setup rather than to worn gear teeth.
• The gears were not run with debris circulating from a failed bearing.

If any of those fail, replace the ring and pinion as a set along with all bearings, the crush sleeve or shim pack, and seals. Reusing half a set or reusing gears that ran in dirty oil produces a repeat howl the customer will hear immediately.

Every reassembly requires setting pinion depth and preload, carrier preload, and backlash to specification, then verifying the pattern in marking compound and confirming a quiet road test through the full speed range, both accelerating and coasting.